Deck 16: Kinetics: Rates and Mechanisms of Chemical Reactions

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Question
Consider the general reaction 5Br-(aq) + BrO3-(aq) + 6H+(aq) 3Br2(aq) + 3H2O(aq)
For this reaction, the rate when expressed as [Br2]/t is the same as

A) -[H2O]/t
B) 3[BrO3-]/t
C) -5[Br-]/t
D) -0.6[Br-]/t
E) none of the above
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Question
A reaction has the following rate law: Rate = k[A][B]2
In experiment 1, the concentrations of A and B are both 0.10 mol L-1; in experiment 2, the concentrations are both 0.30 mol L-1. If the temperature stays constant, what is the value of the ratio, Rate(2)/Rate(1)?

A) 3.0
B) 6.0
C) 9.0
D) 18
E) 27
Question
A reaction is first-order with respect to the reactant R. Which of the following plots will produce a straight line?

A) [R] vs. 1/time
B) 1/[R] vs. time
C) [R]2 vs. time
D) 1/[R]2 vs. time
E) ln[R] vs. time
Question
Consider the reaction 2NH3(g) N2(g) + 3H2(g)
If the rate [H2]/t is 0.030 mol L-1 s-1, then [NH3]/t is

A) -0.045 mol L-1 s-1
B) -0.030 mol L-1 s-1
C) -0.020 mol L-1 s-1
D) -0.010 mol L-1 s-1
E) none of the above
Question
Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr-1 results. What is the rate law for the reaction?

A) Rate = 0.208 hr-1 [sucrose]2
B) Rate = 0.208 hr-1 [sucrose]
C) Rate = 0.0433 hr [sucrose]2
D) Rate = 0.0433 hr [sucrose]
E) Rate = 0.208 mol L-1hr-1 [sucrose]0
Question
The compound RX3 decomposes according to the equation 3RX3 R + R2X3 + 3X2
In an experiment the following data were collected for the decomposition at 100°C. What is the average rate of reaction over the entire experiment? <strong>The compound RX<sub>3</sub> decomposes according to the equation 3RX<sub>3</sub> <font face=symbol></font> R + R<sub>2</sub>X<sub>3 </sub>+ 3X<sub>2</sub> In an experiment the following data were collected for the decomposition at 100°C. What is the average rate of reaction over the entire experiment?  </strong> A) 0.011 mol L<sup>-1</sup>s<sup>-1</sup> B) 0.019 mol L<sup>-1</sup>s<sup>-1</sup> C) 0.044 mol L<sup>-1</sup>s<sup>-1</sup> D) 0.049 mol L<sup>-1</sup>s<sup>-1</sup> E) 0.069 mol L<sup>-1</sup>s<sup>-1</sup> <div style=padding-top: 35px>

A) 0.011 mol L-1s-1
B) 0.019 mol L-1s-1
C) 0.044 mol L-1s-1
D) 0.049 mol L-1s-1
E) 0.069 mol L-1s-1
Question
Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate constant, k, is 3.60 L mol-1s-1. What is the rate law for this reaction?

A) Rate = 3.60 L mol-1s-1[NH4CNO]
B) Rate = 3.60 L mol-1s-1[NH4CNO]2
C) Rate = 0.28 mol L-1 s-1[NH4CNO]
D) Rate = 0.28 mol L-1 s-1[NH4CNO]2
E) Rate = 3.60 L mol-1s-1[NH2CONH2]-1
Question
When the reaction A B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive slope. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
Question
Which of the following sets of units could be appropriate for a zero-order rate constant?

A) s-1
B) L mol-1 s-1
C) L2 mol-2 s-1
D) L3 mol-3 s-1
E) mol L-1 s-1
Question
For the reaction 3A(g) + 2B(g) 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction. <strong>For the reaction 3A(g) + 2B(g) <font face=symbol></font> 2C(g) + 2D(g) The following data were collected at constant temperature. Determine the correct rate law for this reaction.  </strong> A) Rate = k[A][B] B) Rate = k[A][B]<sup>2</sup> C) Rate = k[A]<sup>3</sup>[B]<sup>2</sup> D) Rate = k[A]<sup>1.5</sup>[B] E) Rate = k[A]<sup>2</sup>[B] <div style=padding-top: 35px>

A) Rate = k[A][B]
B) Rate = k[A][B]2
C) Rate = k[A]3[B]2
D) Rate = k[A]1.5[B]
E) Rate = k[A]2[B]
Question
Sulfuryl chloride, SO2Cl2(g), decomposes at high temperature to form SO2(g) and Cl2(g). The rate constant at a certain temperature is 4.68 × 10-5s-1. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
Question
Which one of the following sets of units is appropriate for a third-order rate constant?

A) s-1
B) mol L-1 s-1
C) L mol-1 s-1
D) L2 mol-2 s-1
E) L3 mol-3 s-1
Question
Which one of the following sets of units is appropriate for a second-order rate constant?

A) s-1
B) mol L-1 s-1
C) L mol-1 s-1
D) mol2 L-2 s-1
E) L2 mol-2 s-1
Question
Consider the following reaction 8A(g) + 5B(g) 8C(g) + 6D(g)
If [C] is increasing at the rate of 4.0 mol L-1s-1, at what rate is [B] changing?

A) -0.40 mol L-1s-1
B) -2.5 mol L-1s-1
C) -4.0 mol L-1s-1
D) -6.4 mol L-1s-1
E) none of the above, since its rate of change must be positive
Question
The rate constant for a reaction is 4.65 L mol-1s-1. What is the overall order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the overall order.
Question
Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a slope of 0.0448 L mol-1s-1. What is the rate law for this reaction?

A) Rate = 0.0448 (L mol-1s-1)[C2F4]
B) Rate = 22.3 (mol L-1s)[C2F4]
C) Rate = 0.0448 (L mol-1s-1)[C2F4]2
D) Rate = 22.3 (mol L-1s)[C2F4]2
E) Rate = 0.0448 s-1 [C2F4]
Question
For the reaction A(g) + 2B(g) 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction. <strong>For the reaction A(g) + 2B(g) <font face=symbol></font> 2C(g) + 2D(g) The following data were collected at constant temperature. Determine the correct rate law for this reaction.  </strong> A) Rate = k[A] [B] B) Rate = k[A]<sup>2 </sup>[B] C) Rate = k[A] [B]<sup>2</sup> D) Rate = k[A] E) Rate = k[A]<sup>3</sup> <div style=padding-top: 35px>

A) Rate = k[A] [B]
B) Rate = k[A]2 [B]
C) Rate = k[A] [B]2
D) Rate = k[A]
E) Rate = k[A]3
Question
For the reaction 2A + B + 2C D + E
The following initial rate data were collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary. <strong>For the reaction 2A + B + 2C <font face=symbol></font> D + E The following initial rate data were collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary.  </strong> A) Rate = k[A][B][C] B) Rate = k [A]<sup>2</sup>[B][C] C) Rate = k [A]<sup>2</sup>[B][C]<sup>-1</sup> D) Rate = k [A][B]<sup>2</sup>[C]<sup> -1</sup> E) none of the above <div style=padding-top: 35px>

A) Rate = k[A][B][C]
B) Rate = k [A]2[B][C]
C) Rate = k [A]2[B][C]-1
D) Rate = k [A][B]2[C] -1
E) none of the above
Question
When the reaction A B + C is studied, a plot of ln[A]t vs. time gives a straight line with a negative slope. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
Question
Sulfur trioxide can undergo decomposition according to the equation 2SO3 2SO2 + O2
For this reaction, rate = -0 0.5[SO3]/t = k[SO3]2. If the reaction rate is 1.75 × 10-7 mol L-1 min-1 when the concentration of sulfur trioxide is 5.4 × 10-3 mol L-1, what is the value of the rate constant k?

A) 3.2 × 10-5 L mol-1 min-1
B) 1.6 × 10-5 L mol-1 min-1
C) 6.0 × 10-3 L mol-1 min-1
D) 3.0 × 10-3 L mol-1 min-1
E) 1.6 × 10-2 L mol-1 min-1
Question
The active ingredient in an over the counter pain killer analgesic decomposes with a rate constant, k = 9.05 × 10-4 day-1. How many days does it take for 15% of the original ingredient to decompose?

A) 730 days
B) 414 days
C) 365 days
D) 180 days
E) 78 days
Question
Cyclopropane is converted to propene in a first-order process. The rate constant is 5.4 × 10-2 hr-1. If the initial concentration of cyclopropane is 0.150 M, what will its concentration be after 22.0 hours?

A) 0.0457 M
B) 0.105 M
C) 0.127 M
D) 0.492 M
E) none of the above
Question
A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 1020 molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

A) 1.00 × 104 molecules
B) 2.00 × 1019 molecules
C) 3.20 × 1016 molecules
D) 5.00 × 1020 molecules
E) none of the above
Question
Ammonia will react with oxygen in the presence of a copper catalyst to form nitrogen and water. From 164.5°C to 179.0°C, the rate constant increases by a factor of 4.27. What is the activation energy of this oxidation reaction?

A) 24.5 kJ/mol
B) 165 kJ/mol
C) 242 kJ/mol
D) 1630 kJ/mol
E) > 104 kJ/mol
Question
In going from room temperature (25.0 °C) to 10 °C above room temperature, the rate of a reaction doubles. Calculate the activation energy for the reaction.

A) 157.2 kJ/mol
B) 103.8 kJ/mol
C) 52.9 kJ/mol
D) 6.4 kJ/mol
E) <1 kJ/mol
Question
A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10-4 mol L-1 and the rate constant k = 1.08 × 10-6 s-1, what concentration of R remains after 25 days?

A) 1.0 × 10-3 mol L-1
B) 1.0 × 10-4 mol L-1
C) 9.6 × 10-5 mol L-1
D) 4.3 × 10-5 mol L-1
E) 9.7 × 10-6 mol L-1
Question
The reaction CH3NC(g) CH3CN(g) is first-order with respect to methyl isocyanide, CH3NC. If it takes 10.3 minutes for exactly one quarter of the initial amount of methyl isocyanide to react, what is the rate constant in units of min-1?

A) -0.135 min-1
B) 0.0279 min-1
C) 0.089 min-1
D) 0.135 min-1
E) 35.8 min-1
Question
A reaction is second-order with respect to the reactant R. Which of the following plots will produce a straight line?

A) [R] vs. 1/time
B) 1/[R] vs. time
C) [R]2 vs. time
D) 1/[R]2 vs. time
E) ln[R] vs. time
Question
A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?

A) 0.94
B) 0.87
C) 0.75
D) 0.13
E) 0.063
Question
The rate law for the reaction 3A C is Rate = 4.36 × 10-2 L mol-1 hr-1[A]2
What is the half-life for the reaction if the initial concentration of A is 0.250 M?

A) 0.0109 hr
B) 0.0629 hr
C) 15.9 hr
D) 23.9 hr
E) 91.7 hr
Question
Dinitrogen tetraoxide, N2O4, decomposes to nitrogen dioxide, NO2, in a first-order process. If k = 2.5 × 103 s-1 at -5°C and k = 3.5 × 104 s-1 at 25°C, what is the activation energy for the decomposition?

A) 0.73 kJ/mol
B) 58 kJ/mol
C) 140 kJ/mol
D) 580 kJ/mol
E) > 1000 kJ/mol
Question
The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year-1. What fraction of the tritium initially in a sample is still present 30 years later?

A) 0.19
B) 0.60
C) 0.15
D) 2.8 × 10-38
E) none of the above
Question
The decomposition of SOCl2 is first-order in SOCl2. If the half-life for the reaction is 4.1 hr, how long would it take for the concentration of SOCl2 to drop from 0.36 M to 0.045 M?

A) 0.52 hr
B) 1.4 hr
C) 12 hr
D) 33 hr
E) > 40 hr
Question
The reaction X Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

A) shorten the half-life of the reaction.
B) increase the rate constant of the reaction.
C) decrease the rate constant of the reaction.
D) shorten the time taken to reach equilibrium.
E) double the initial rate.
Question
Carbon-14 is a radioactive isotope which decays with a half-life of 5730 years. What is the first-order rate constant for its decay, in units of years-1?

A) 5.25 × 10-5 years-1
B) 1.21 × 10-4 years-1
C) 1.75 × 10-4 years-1
D) 3.49 × 10-4 years-1
E) 3.97 × 103 years-1
Question
The rate law for the reaction 3A 2B is rate = k[A] with a rate constant of 0.0447 hr-1. What is the half-life of the reaction?

A) 0.0224 hr
B) 0.0645 hr
C) 15.5 hr
D) 22.4 hr
E) 44.7 hr
Question
Butadiene, C4H6 (used to make synthetic rubber and latex paints) reacts to C8H12 with a rate law of rate = 0.014 L/(mol·s) [C4H6]2. What will be the concentration of C4H6 after 3.0 hours if the initial concentration is 0.025 M?

A) 0.0052 M
B) 0.024 M
C) 43 M
D) 190 M
E) 0.0000 M
Question
The decomposition of hydrogen peroxide is a first-order process with a rate constant of 1.06 × 10-3 min-1. How long will it take for the concentration of H2O2 to drop from 0.0200 M to 0.0120 M?

A) < 1 min
B) 7.55 min
C) 481 min
D) 4550 min
E) 31,400 min
Question
The rate law for the rearrangement of CH3NC to CH3CN at 800 K is Rate = (1300 s-1)[CH3NC]. What is the half-life for this reaction?

A) 7.69 × 10-4 s
B) 5.3 × 10-4 s
C) 1.9 × 10-3 s
D) 520 s
E) 1920 s
Question
The rate constant for the reaction 3A 4B is 6.00 × 10-3 L mol-1min-1. How long will it take the concentration of A to drop from 0.75 M to 0.25 M?

A) 2.2 × 10-3 min
B) 5.5 × 10-3 min
C) 180 min
D) 440 min
E) 5.0 × 102 min
Question
A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 1013 s-1 and the activation energy being 150. kJ mol-1. What is the value of the rate constant at 227°C, in s-1?

A) 2.1 × 1013 s-1
B) 6.7 × 10-22 s-1
C) 1.5 × 1011 s-1
D) 4.7 × 10-3 s-1
E) none of the above
Question
An increase in temperature increases the reaction rate because

A) a greater fraction of the collisions have the correct orientation of molecules.
B) the activation energy of the reaction will increase.
C) the activation energy of the reaction will decrease.
D) temperature acts as a catalyst in chemical reactions.
E) more collisions will have enough energy to exceed the activation energy.
Question
In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of
a. the rate of the reaction, 600. seconds after the start.
b. the half-life of the reaction, t1/2. In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of a. the rate of the reaction, 600. seconds after the start. b. the half-life of the reaction, t<sub>1/2</sub>.  <div style=padding-top: 35px>
Question
Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2 <strong>Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H<sup>+</sup> + H<sub>2</sub>O<sub>2</sub>   H<sub>2</sub>O<sup>+</sup>-OH (rapid equilibrium) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> <font face=symbol></font> HOBr + H<sub>2</sub>O (slow) HOBr + H<sup>+</sup> + Br<sup>-</sup> <font face=symbol></font> Br<sub>2</sub> + H<sub>2</sub>O (fast) Which of the following rate laws is consistent with the mechanism?</strong> A) Rate = k[H<sub>2</sub>O<sub>2</sub>][H<sup>+</sup>]<sup>2</sup>[Br<sup>-</sup>] B) Rate = k [H<sub>2</sub>O<sup>+</sup>-OH][Br<sup>-</sup>] C) Rate = k[H<sub>2</sub>O<sub>2</sub>][H<sup>+</sup>][Br<sup>-</sup>] D) Rate = k[HOBr][H<sup>+</sup>][Br<sup>-</sup>][H<sub>2</sub>O<sub>2</sub>] E) Rate = k[Br<sup>-</sup>] <div style=padding-top: 35px> H2O+-OH (rapid equilibrium)
H2O+-OH + Br- HOBr + H2O (slow)
HOBr + H+ + Br- Br2 + H2O (fast)
Which of the following rate laws is consistent with the mechanism?

A) Rate = k[H2O2][H+]2[Br-]
B) Rate = k [H2O+-OH][Br-]
C) Rate = k[H2O2][H+][Br-]
D) Rate = k[HOBr][H+][Br-][H2O2]
E) Rate = k[Br-]
Question
The kinetics of the decomposition of dinitrogen pentaoxide is studied at 50°C and at 75°C. Which of the following statements concerning the studies is correct?

A) The rate at 75°C will be greater than the rate at 50°C because the activation energy will be lower at 75°C than at 50°C.
B) The rate at 75°C will be greater than the rate at 50°C because the activation energy will be higher at 75°C than at 50°C.
C) The rate at 75°C will be less than the rate at 50°C because the molecules at higher speeds do not interact as well as those at lower speeds.
D) The rate at 75°C will be greater than at 50°C because the concentration of a gas increases with increasing temperature.
E) The rate at 75°C will be greater than the rate at 50°C because the number of molecules with enough energy to react increases with increasing temperature.
Question
If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0 kJ/mol, what effect will this have on the rate of reaction at 298K?

A) The rate will increase, by a factor of more than 50.
B) The rate will decrease, by a factor of more than 50.
C) The rate will increase, by a factor of less than 50.
D) The rate will decrease, by a factor of less than 50.
E) The rate will not change unless temperature changes.
Question
The decomposition of dinitrogen pentaoxide to nitrogen dioxide and oxygen follows first-order kinetics and has an activation energy of 102 kJ/mol. By what factor will the fraction of collisions with energy greater than or equal to the activation energy increase if the reaction temperature goes from 30°C to 60°C?

A) 1.00
B) 1.10
C) 2.00
D) 4.00
E) 38.4
Question
A catalyst accelerates a reaction because

A) it increases the number of molecules with energy equal to or greater than the activation energy.
B) it lowers the activation energy for the reaction.
C) it increases the number of collisions between molecules.
D) it increases the temperature of the molecules in the reaction.
E) it supplies energy to reactant molecules.
Question
What is the molecularity of the following elementary reaction? NH2Cl(aq) + OH-(aq) NHCl-(aq) + H2O(l)

A) unimolecular
B) bimolecular
C) termolecular
D) tetramolecular
E) Need to know the reaction order before molecularity can be determined.
Question
Which of the following affects the activation energy of a reaction?

A) temperature of the reactants
B) concentrations of reactants
C) presence of a catalyst
D) surface area of reactants
E) reaction progress
Question
A boiled egg can be cooked at 100.0 °C in exactly 5 minutes. At an altitude of around 2000 m where the boiling point of water is 93.0 °C, it takes exactly 7.5 minutes to cook the egg to the same amount. What is the activation energy for the reaction involved when an egg is boiled?

A) 0.5 kJ/mol
B) 4.5 kJ/mol
C) 7.9 kJ/mol
D) 66 kJ/mol
E) >100 kJ/mol
Question
Reaction intermediates differ from activated complexes in that

A) they are stable molecules with normal bonds and are frequently isolated.
B) they are molecules with normal bonds rather than partial bonds and can occasionally be isolated.
C) they are intermediate structures which have characteristics of both reactants and products.
D) they are unstable and can never be isolated.
E) all reactions involve reaction intermediates, but not all have activated complexes.
Question
The gas-phase reaction CH3NC CH3CN has been studied in a closed vessel, and the rate equation was found to be: Rate = -[CH3NC]/t = k[CH3NC]. Which one of the following actions is least likely to cause a change in the rate of the reaction?

A) lowering the temperature
B) adding a catalyst
C) using a larger initial amount of CH3NC in the same vessel
D) using a bigger vessel, but the same initial amount of CH3NC
E) continuously removing CH3CN as it is formed
Question
The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and rxn = + 55 kJ/mol. What is the activation energy for the reverse reaction?

A) 27 kJ/mol
B) 47 kJ/mol
C) 55 kJ/mol
D) 102 kJ/mol
E) More information is needed, since this is a Hess's law calculation.
Question
Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2 <strong>Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H<sup>+ </sup> + H<sub>2</sub>O<sub>2</sub>   H<sub>2</sub>O<sup>+</sup>-OH (rapid equilibrium) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> <font face=symbol></font> HOBr + H<sub>2</sub>O (slow) HOBr + H<sup>+</sup> + Br<sup>-</sup> <font face=symbol></font> Br<sub>2 </sub>+ H<sub>2</sub>O (fast) What is the overall reaction equation for this process?</strong> A) 2H<sub>2</sub>O<sup>+</sup>-OH + 2Br<sup>- </sup> <font face=symbol></font> H<sub>2</sub>O<sub>2 </sub>+ Br<sub>2 </sub>+ 2H<sub>2</sub>O B) 2H<sup>+</sup> + 2Br<sup>-</sup> + H<sub>2</sub>O<sub>2 </sub><font face=symbol></font> Br<sub>2 </sub>+ 2H<sub>2</sub>O C) 2H<sup>+</sup> + H<sub>2</sub>O<sub>2 </sub>+ Br<sup>-</sup> + HOBr <font face=symbol></font> H<sub>2</sub>O<sup>+</sup>-OH + Br<sub>2 </sub>+ H<sub>2</sub>O D) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> + H<sup>+</sup> <font face=symbol></font> Br<sub>2 </sub>+ H<sub>2</sub>O E) none of the above <div style=padding-top: 35px> H2O+-OH (rapid equilibrium)
H2O+-OH + Br- HOBr + H2O (slow)
HOBr + H+ + Br- Br2 + H2O (fast)
What is the overall reaction equation for this process?

A) 2H2O+-OH + 2Br- H2O2 + Br2 + 2H2O
B) 2H+ + 2Br- + H2O2 Br2 + 2H2O
C) 2H+ + H2O2 + Br- + HOBr H2O+-OH + Br2 + H2O
D) H2O+-OH + Br- + H+ Br2 + H2O
E) none of the above
Question
In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time. In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time.   a. Explain how this plot confirms that the reaction is first order. b. Calculate the first-order rate constant, k. c. Determine the initial concentration of cyclopropane in this experiment.<div style=padding-top: 35px> a. Explain how this plot confirms that the reaction is first order.
b. Calculate the first-order rate constant, k.
c. Determine the initial concentration of
cyclopropane in this experiment.
Question
When a catalyst is added to a reaction mixture, it

A) increases the rate of collisions between reactant molecules.
B) provides reactant molecules with more energy.
C) slows down the rate of the back reaction.
D) provides a new pathway (mechanism) for the reaction.
E) does none of the above.
Question
A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200.°C to 220.°C, the rate constant will increase by a factor of

A) 1.1.
B) 4.3 × 104.
C) 3.2.
D) 7.5.
E) none of the above.
Question
You are studying the rate of the reaction 2A B and have obtained measurements of the concentration of A at times t = 100, 200, 300, ......, 1000 seconds from the start of the reaction. Carefully describe how you would plot a graph and use it to
a. prove that the reaction is second-order with respect to A.
b. determine the second-order rate constant k.
Question
In an exothermic reaction,

A) the forward reaction is slower than the reverse reaction.
B) the reaction rate will speed up with time.
C) the collision energy of the reactants will be greater than that of the products.
D) the forward reaction will have a lower activation energy than the reverse reaction.
E) the activation energy will change as the reaction progresses.
Question
Briefly list the features/properties common to all catalysts and how they work. Draw a labeled reaction energy diagram as part of your answer.
Question
The units of the rate of reaction depend on the order of the reaction.
Question
The greater the energy of activation, Ea, the faster will be the reaction.
Question
At 25.0°C, a rate constant has the value 5.21 × 10-8 L mol-1 s-1. If the activation energy is 75.2 kJ/mol, calculate the rate constant when the temperature is 50.0°C.
Question
The half-life of a second-order reaction does not depend on the initial concentration of reactant.
Question
The rate law cannot be predicted from the stoichiometry of a reaction.
Question
In the collision theory of reaction rates, the rate constant for a bimolecular reaction can be written as
k = zpexp(-Ea/RT)
In one sentence each, clearly explain the physical meaning (interpretation) of the following three factors which appear in the above expression:
a. z
b. p
c. exp(-Ea/RT)
Question
For each of the following terms/concepts, give a brief explanation or definition. Where possible, use examples.
a. order of a reaction
b. elementary reaction
c. reaction intermediate
Question
According to the collision theory of reaction rates, what are the three requirements which must be met before an elementary reaction between two molecules can occur?
Question
The half-life of a first-order reaction does not depend on the initial concentration of reactant.
Question
Briefly outline the key arguments in the collision theory of reaction rates for the elementary reaction
C + D products
Show that this theory predicts a second-order rate law, and how it predicts the form of the rate constant k.
Question
The elementary reaction HBr(g) + Br(g) H(g) + Br2(g) is endothermic.
a. Would you expect the rate constant for the back reaction to be smaller or larger than that for the forward reaction? Explain, briefly.
b. Draw a fully-labeled reaction energy diagram for this reaction, showing the locations of the reactants, products, and transition state.
Question
Is a bimolecular reaction necessarily second-order? Is a second-order reaction necessarily bimolecular? Answer, with explanations and clarifications.
Question
A chemical reaction of the general type
A 2B
is first-order, with a rate constant of 1.52 × 10-4 s-1.
a. Calculate the half-life of A.
b. Assuming the initial concentration of A is 0.067 mol L-1, calculate the time needed for the concentration to fall to 0.010 mol L-1.
Question
You are required to determine the energy of activation (Ea) of a reaction. Briefly describe the experimental measurements you would make and how you would obtain the activation energy from a suitable linear plot of the experimental data.
Question
Cyclobutane decomposes to ethene in a first-order reaction. From measurements of the rate constant (k) at various absolute temperatures (T), the accompanying Arrhenius plot was obtained (ln k versus 1/T). Cyclobutane decomposes to ethene in a first-order reaction. From measurements of the rate constant (k) at various absolute temperatures (T), the accompanying Arrhenius plot was obtained (ln k versus 1/T).   a. Calculate the energy of activation, E<sub>a</sub>. b. Determine the value of the rate constant at 740. K. (In the plot, the units of k are s<sup>-1</sup>.)<div style=padding-top: 35px> a. Calculate the energy of activation, Ea.
b. Determine the value of the rate constant at 740. K. (In the plot, the units of k are s-1.)
Question
An elementary reaction is a simple, one-step process.
Question
The gas-phase conversion of 1,3-butadiene to 1,5-cyclooctadiene, 2C4H6 C8H12 was studied, providing data for the plot shown, of 1/[butadiene] versus time. The gas-phase conversion of 1,3-butadiene to 1,5-cyclooctadiene, 2C<sub>4</sub>H<sub>6</sub> <font face=symbol></font> C<sub>8</sub>H<sub>12</sub> was studied, providing data for the plot shown, of 1/[butadiene] versus time.   a. Explain how this plot confirms that the reaction is second order. b. Calculate the second-order rate constant, k. c. Determine the initial concentration of 1,3-butadiene in this experiment.<div style=padding-top: 35px> a. Explain how this plot confirms that the reaction is second order.
b. Calculate the second-order rate constant, k.
c. Determine the initial concentration of 1,3-butadiene in this experiment.
Question
All second-order reactions are bimolecular reactions.
Question
The units of the rate constant depend on the order of the reaction.
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Deck 16: Kinetics: Rates and Mechanisms of Chemical Reactions
1
Consider the general reaction 5Br-(aq) + BrO3-(aq) + 6H+(aq) 3Br2(aq) + 3H2O(aq)
For this reaction, the rate when expressed as [Br2]/t is the same as

A) -[H2O]/t
B) 3[BrO3-]/t
C) -5[Br-]/t
D) -0.6[Br-]/t
E) none of the above
-0.6[Br-]/t
2
A reaction has the following rate law: Rate = k[A][B]2
In experiment 1, the concentrations of A and B are both 0.10 mol L-1; in experiment 2, the concentrations are both 0.30 mol L-1. If the temperature stays constant, what is the value of the ratio, Rate(2)/Rate(1)?

A) 3.0
B) 6.0
C) 9.0
D) 18
E) 27
27
3
A reaction is first-order with respect to the reactant R. Which of the following plots will produce a straight line?

A) [R] vs. 1/time
B) 1/[R] vs. time
C) [R]2 vs. time
D) 1/[R]2 vs. time
E) ln[R] vs. time
ln[R] vs. time
4
Consider the reaction 2NH3(g) N2(g) + 3H2(g)
If the rate [H2]/t is 0.030 mol L-1 s-1, then [NH3]/t is

A) -0.045 mol L-1 s-1
B) -0.030 mol L-1 s-1
C) -0.020 mol L-1 s-1
D) -0.010 mol L-1 s-1
E) none of the above
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5
Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of -0.208 hr-1 results. What is the rate law for the reaction?

A) Rate = 0.208 hr-1 [sucrose]2
B) Rate = 0.208 hr-1 [sucrose]
C) Rate = 0.0433 hr [sucrose]2
D) Rate = 0.0433 hr [sucrose]
E) Rate = 0.208 mol L-1hr-1 [sucrose]0
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6
The compound RX3 decomposes according to the equation 3RX3 R + R2X3 + 3X2
In an experiment the following data were collected for the decomposition at 100°C. What is the average rate of reaction over the entire experiment? <strong>The compound RX<sub>3</sub> decomposes according to the equation 3RX<sub>3</sub> <font face=symbol></font> R + R<sub>2</sub>X<sub>3 </sub>+ 3X<sub>2</sub> In an experiment the following data were collected for the decomposition at 100°C. What is the average rate of reaction over the entire experiment?  </strong> A) 0.011 mol L<sup>-1</sup>s<sup>-1</sup> B) 0.019 mol L<sup>-1</sup>s<sup>-1</sup> C) 0.044 mol L<sup>-1</sup>s<sup>-1</sup> D) 0.049 mol L<sup>-1</sup>s<sup>-1</sup> E) 0.069 mol L<sup>-1</sup>s<sup>-1</sup>

A) 0.011 mol L-1s-1
B) 0.019 mol L-1s-1
C) 0.044 mol L-1s-1
D) 0.049 mol L-1s-1
E) 0.069 mol L-1s-1
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7
Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate constant, k, is 3.60 L mol-1s-1. What is the rate law for this reaction?

A) Rate = 3.60 L mol-1s-1[NH4CNO]
B) Rate = 3.60 L mol-1s-1[NH4CNO]2
C) Rate = 0.28 mol L-1 s-1[NH4CNO]
D) Rate = 0.28 mol L-1 s-1[NH4CNO]2
E) Rate = 3.60 L mol-1s-1[NH2CONH2]-1
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8
When the reaction A B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive slope. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
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9
Which of the following sets of units could be appropriate for a zero-order rate constant?

A) s-1
B) L mol-1 s-1
C) L2 mol-2 s-1
D) L3 mol-3 s-1
E) mol L-1 s-1
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10
For the reaction 3A(g) + 2B(g) 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction. <strong>For the reaction 3A(g) + 2B(g) <font face=symbol></font> 2C(g) + 2D(g) The following data were collected at constant temperature. Determine the correct rate law for this reaction.  </strong> A) Rate = k[A][B] B) Rate = k[A][B]<sup>2</sup> C) Rate = k[A]<sup>3</sup>[B]<sup>2</sup> D) Rate = k[A]<sup>1.5</sup>[B] E) Rate = k[A]<sup>2</sup>[B]

A) Rate = k[A][B]
B) Rate = k[A][B]2
C) Rate = k[A]3[B]2
D) Rate = k[A]1.5[B]
E) Rate = k[A]2[B]
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11
Sulfuryl chloride, SO2Cl2(g), decomposes at high temperature to form SO2(g) and Cl2(g). The rate constant at a certain temperature is 4.68 × 10-5s-1. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
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12
Which one of the following sets of units is appropriate for a third-order rate constant?

A) s-1
B) mol L-1 s-1
C) L mol-1 s-1
D) L2 mol-2 s-1
E) L3 mol-3 s-1
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13
Which one of the following sets of units is appropriate for a second-order rate constant?

A) s-1
B) mol L-1 s-1
C) L mol-1 s-1
D) mol2 L-2 s-1
E) L2 mol-2 s-1
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14
Consider the following reaction 8A(g) + 5B(g) 8C(g) + 6D(g)
If [C] is increasing at the rate of 4.0 mol L-1s-1, at what rate is [B] changing?

A) -0.40 mol L-1s-1
B) -2.5 mol L-1s-1
C) -4.0 mol L-1s-1
D) -6.4 mol L-1s-1
E) none of the above, since its rate of change must be positive
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15
The rate constant for a reaction is 4.65 L mol-1s-1. What is the overall order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the overall order.
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16
Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a slope of 0.0448 L mol-1s-1. What is the rate law for this reaction?

A) Rate = 0.0448 (L mol-1s-1)[C2F4]
B) Rate = 22.3 (mol L-1s)[C2F4]
C) Rate = 0.0448 (L mol-1s-1)[C2F4]2
D) Rate = 22.3 (mol L-1s)[C2F4]2
E) Rate = 0.0448 s-1 [C2F4]
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17
For the reaction A(g) + 2B(g) 2C(g) + 2D(g)
The following data were collected at constant temperature. Determine the correct rate law for this reaction. <strong>For the reaction A(g) + 2B(g) <font face=symbol></font> 2C(g) + 2D(g) The following data were collected at constant temperature. Determine the correct rate law for this reaction.  </strong> A) Rate = k[A] [B] B) Rate = k[A]<sup>2 </sup>[B] C) Rate = k[A] [B]<sup>2</sup> D) Rate = k[A] E) Rate = k[A]<sup>3</sup>

A) Rate = k[A] [B]
B) Rate = k[A]2 [B]
C) Rate = k[A] [B]2
D) Rate = k[A]
E) Rate = k[A]3
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18
For the reaction 2A + B + 2C D + E
The following initial rate data were collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary. <strong>For the reaction 2A + B + 2C <font face=symbol></font> D + E The following initial rate data were collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary.  </strong> A) Rate = k[A][B][C] B) Rate = k [A]<sup>2</sup>[B][C] C) Rate = k [A]<sup>2</sup>[B][C]<sup>-1</sup> D) Rate = k [A][B]<sup>2</sup>[C]<sup> -1</sup> E) none of the above

A) Rate = k[A][B][C]
B) Rate = k [A]2[B][C]
C) Rate = k [A]2[B][C]-1
D) Rate = k [A][B]2[C] -1
E) none of the above
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19
When the reaction A B + C is studied, a plot of ln[A]t vs. time gives a straight line with a negative slope. What is the order of the reaction?

A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
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20
Sulfur trioxide can undergo decomposition according to the equation 2SO3 2SO2 + O2
For this reaction, rate = -0 0.5[SO3]/t = k[SO3]2. If the reaction rate is 1.75 × 10-7 mol L-1 min-1 when the concentration of sulfur trioxide is 5.4 × 10-3 mol L-1, what is the value of the rate constant k?

A) 3.2 × 10-5 L mol-1 min-1
B) 1.6 × 10-5 L mol-1 min-1
C) 6.0 × 10-3 L mol-1 min-1
D) 3.0 × 10-3 L mol-1 min-1
E) 1.6 × 10-2 L mol-1 min-1
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21
The active ingredient in an over the counter pain killer analgesic decomposes with a rate constant, k = 9.05 × 10-4 day-1. How many days does it take for 15% of the original ingredient to decompose?

A) 730 days
B) 414 days
C) 365 days
D) 180 days
E) 78 days
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22
Cyclopropane is converted to propene in a first-order process. The rate constant is 5.4 × 10-2 hr-1. If the initial concentration of cyclopropane is 0.150 M, what will its concentration be after 22.0 hours?

A) 0.0457 M
B) 0.105 M
C) 0.127 M
D) 0.492 M
E) none of the above
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23
A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 1020 molecules of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?

A) 1.00 × 104 molecules
B) 2.00 × 1019 molecules
C) 3.20 × 1016 molecules
D) 5.00 × 1020 molecules
E) none of the above
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24
Ammonia will react with oxygen in the presence of a copper catalyst to form nitrogen and water. From 164.5°C to 179.0°C, the rate constant increases by a factor of 4.27. What is the activation energy of this oxidation reaction?

A) 24.5 kJ/mol
B) 165 kJ/mol
C) 242 kJ/mol
D) 1630 kJ/mol
E) > 104 kJ/mol
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25
In going from room temperature (25.0 °C) to 10 °C above room temperature, the rate of a reaction doubles. Calculate the activation energy for the reaction.

A) 157.2 kJ/mol
B) 103.8 kJ/mol
C) 52.9 kJ/mol
D) 6.4 kJ/mol
E) <1 kJ/mol
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26
A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10-4 mol L-1 and the rate constant k = 1.08 × 10-6 s-1, what concentration of R remains after 25 days?

A) 1.0 × 10-3 mol L-1
B) 1.0 × 10-4 mol L-1
C) 9.6 × 10-5 mol L-1
D) 4.3 × 10-5 mol L-1
E) 9.7 × 10-6 mol L-1
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27
The reaction CH3NC(g) CH3CN(g) is first-order with respect to methyl isocyanide, CH3NC. If it takes 10.3 minutes for exactly one quarter of the initial amount of methyl isocyanide to react, what is the rate constant in units of min-1?

A) -0.135 min-1
B) 0.0279 min-1
C) 0.089 min-1
D) 0.135 min-1
E) 35.8 min-1
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28
A reaction is second-order with respect to the reactant R. Which of the following plots will produce a straight line?

A) [R] vs. 1/time
B) 1/[R] vs. time
C) [R]2 vs. time
D) 1/[R]2 vs. time
E) ln[R] vs. time
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29
A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives?

A) 0.94
B) 0.87
C) 0.75
D) 0.13
E) 0.063
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30
The rate law for the reaction 3A C is Rate = 4.36 × 10-2 L mol-1 hr-1[A]2
What is the half-life for the reaction if the initial concentration of A is 0.250 M?

A) 0.0109 hr
B) 0.0629 hr
C) 15.9 hr
D) 23.9 hr
E) 91.7 hr
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31
Dinitrogen tetraoxide, N2O4, decomposes to nitrogen dioxide, NO2, in a first-order process. If k = 2.5 × 103 s-1 at -5°C and k = 3.5 × 104 s-1 at 25°C, what is the activation energy for the decomposition?

A) 0.73 kJ/mol
B) 58 kJ/mol
C) 140 kJ/mol
D) 580 kJ/mol
E) > 1000 kJ/mol
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32
The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year-1. What fraction of the tritium initially in a sample is still present 30 years later?

A) 0.19
B) 0.60
C) 0.15
D) 2.8 × 10-38
E) none of the above
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33
The decomposition of SOCl2 is first-order in SOCl2. If the half-life for the reaction is 4.1 hr, how long would it take for the concentration of SOCl2 to drop from 0.36 M to 0.045 M?

A) 0.52 hr
B) 1.4 hr
C) 12 hr
D) 33 hr
E) > 40 hr
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34
The reaction X Y is first-order overall and first-order with respect to the reactant X. The result of doubling the initial concentration of X will be to

A) shorten the half-life of the reaction.
B) increase the rate constant of the reaction.
C) decrease the rate constant of the reaction.
D) shorten the time taken to reach equilibrium.
E) double the initial rate.
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35
Carbon-14 is a radioactive isotope which decays with a half-life of 5730 years. What is the first-order rate constant for its decay, in units of years-1?

A) 5.25 × 10-5 years-1
B) 1.21 × 10-4 years-1
C) 1.75 × 10-4 years-1
D) 3.49 × 10-4 years-1
E) 3.97 × 103 years-1
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36
The rate law for the reaction 3A 2B is rate = k[A] with a rate constant of 0.0447 hr-1. What is the half-life of the reaction?

A) 0.0224 hr
B) 0.0645 hr
C) 15.5 hr
D) 22.4 hr
E) 44.7 hr
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37
Butadiene, C4H6 (used to make synthetic rubber and latex paints) reacts to C8H12 with a rate law of rate = 0.014 L/(mol·s) [C4H6]2. What will be the concentration of C4H6 after 3.0 hours if the initial concentration is 0.025 M?

A) 0.0052 M
B) 0.024 M
C) 43 M
D) 190 M
E) 0.0000 M
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38
The decomposition of hydrogen peroxide is a first-order process with a rate constant of 1.06 × 10-3 min-1. How long will it take for the concentration of H2O2 to drop from 0.0200 M to 0.0120 M?

A) < 1 min
B) 7.55 min
C) 481 min
D) 4550 min
E) 31,400 min
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39
The rate law for the rearrangement of CH3NC to CH3CN at 800 K is Rate = (1300 s-1)[CH3NC]. What is the half-life for this reaction?

A) 7.69 × 10-4 s
B) 5.3 × 10-4 s
C) 1.9 × 10-3 s
D) 520 s
E) 1920 s
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40
The rate constant for the reaction 3A 4B is 6.00 × 10-3 L mol-1min-1. How long will it take the concentration of A to drop from 0.75 M to 0.25 M?

A) 2.2 × 10-3 min
B) 5.5 × 10-3 min
C) 180 min
D) 440 min
E) 5.0 × 102 min
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41
A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 1013 s-1 and the activation energy being 150. kJ mol-1. What is the value of the rate constant at 227°C, in s-1?

A) 2.1 × 1013 s-1
B) 6.7 × 10-22 s-1
C) 1.5 × 1011 s-1
D) 4.7 × 10-3 s-1
E) none of the above
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42
An increase in temperature increases the reaction rate because

A) a greater fraction of the collisions have the correct orientation of molecules.
B) the activation energy of the reaction will increase.
C) the activation energy of the reaction will decrease.
D) temperature acts as a catalyst in chemical reactions.
E) more collisions will have enough energy to exceed the activation energy.
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43
In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of
a. the rate of the reaction, 600. seconds after the start.
b. the half-life of the reaction, t1/2. In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of a. the rate of the reaction, 600. seconds after the start. b. the half-life of the reaction, t<sub>1/2</sub>.
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44
Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2 <strong>Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H<sup>+</sup> + H<sub>2</sub>O<sub>2</sub>   H<sub>2</sub>O<sup>+</sup>-OH (rapid equilibrium) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> <font face=symbol></font> HOBr + H<sub>2</sub>O (slow) HOBr + H<sup>+</sup> + Br<sup>-</sup> <font face=symbol></font> Br<sub>2</sub> + H<sub>2</sub>O (fast) Which of the following rate laws is consistent with the mechanism?</strong> A) Rate = k[H<sub>2</sub>O<sub>2</sub>][H<sup>+</sup>]<sup>2</sup>[Br<sup>-</sup>] B) Rate = k [H<sub>2</sub>O<sup>+</sup>-OH][Br<sup>-</sup>] C) Rate = k[H<sub>2</sub>O<sub>2</sub>][H<sup>+</sup>][Br<sup>-</sup>] D) Rate = k[HOBr][H<sup>+</sup>][Br<sup>-</sup>][H<sub>2</sub>O<sub>2</sub>] E) Rate = k[Br<sup>-</sup>] H2O+-OH (rapid equilibrium)
H2O+-OH + Br- HOBr + H2O (slow)
HOBr + H+ + Br- Br2 + H2O (fast)
Which of the following rate laws is consistent with the mechanism?

A) Rate = k[H2O2][H+]2[Br-]
B) Rate = k [H2O+-OH][Br-]
C) Rate = k[H2O2][H+][Br-]
D) Rate = k[HOBr][H+][Br-][H2O2]
E) Rate = k[Br-]
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45
The kinetics of the decomposition of dinitrogen pentaoxide is studied at 50°C and at 75°C. Which of the following statements concerning the studies is correct?

A) The rate at 75°C will be greater than the rate at 50°C because the activation energy will be lower at 75°C than at 50°C.
B) The rate at 75°C will be greater than the rate at 50°C because the activation energy will be higher at 75°C than at 50°C.
C) The rate at 75°C will be less than the rate at 50°C because the molecules at higher speeds do not interact as well as those at lower speeds.
D) The rate at 75°C will be greater than at 50°C because the concentration of a gas increases with increasing temperature.
E) The rate at 75°C will be greater than the rate at 50°C because the number of molecules with enough energy to react increases with increasing temperature.
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46
If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0 kJ/mol, what effect will this have on the rate of reaction at 298K?

A) The rate will increase, by a factor of more than 50.
B) The rate will decrease, by a factor of more than 50.
C) The rate will increase, by a factor of less than 50.
D) The rate will decrease, by a factor of less than 50.
E) The rate will not change unless temperature changes.
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47
The decomposition of dinitrogen pentaoxide to nitrogen dioxide and oxygen follows first-order kinetics and has an activation energy of 102 kJ/mol. By what factor will the fraction of collisions with energy greater than or equal to the activation energy increase if the reaction temperature goes from 30°C to 60°C?

A) 1.00
B) 1.10
C) 2.00
D) 4.00
E) 38.4
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48
A catalyst accelerates a reaction because

A) it increases the number of molecules with energy equal to or greater than the activation energy.
B) it lowers the activation energy for the reaction.
C) it increases the number of collisions between molecules.
D) it increases the temperature of the molecules in the reaction.
E) it supplies energy to reactant molecules.
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49
What is the molecularity of the following elementary reaction? NH2Cl(aq) + OH-(aq) NHCl-(aq) + H2O(l)

A) unimolecular
B) bimolecular
C) termolecular
D) tetramolecular
E) Need to know the reaction order before molecularity can be determined.
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50
Which of the following affects the activation energy of a reaction?

A) temperature of the reactants
B) concentrations of reactants
C) presence of a catalyst
D) surface area of reactants
E) reaction progress
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51
A boiled egg can be cooked at 100.0 °C in exactly 5 minutes. At an altitude of around 2000 m where the boiling point of water is 93.0 °C, it takes exactly 7.5 minutes to cook the egg to the same amount. What is the activation energy for the reaction involved when an egg is boiled?

A) 0.5 kJ/mol
B) 4.5 kJ/mol
C) 7.9 kJ/mol
D) 66 kJ/mol
E) >100 kJ/mol
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52
Reaction intermediates differ from activated complexes in that

A) they are stable molecules with normal bonds and are frequently isolated.
B) they are molecules with normal bonds rather than partial bonds and can occasionally be isolated.
C) they are intermediate structures which have characteristics of both reactants and products.
D) they are unstable and can never be isolated.
E) all reactions involve reaction intermediates, but not all have activated complexes.
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53
The gas-phase reaction CH3NC CH3CN has been studied in a closed vessel, and the rate equation was found to be: Rate = -[CH3NC]/t = k[CH3NC]. Which one of the following actions is least likely to cause a change in the rate of the reaction?

A) lowering the temperature
B) adding a catalyst
C) using a larger initial amount of CH3NC in the same vessel
D) using a bigger vessel, but the same initial amount of CH3NC
E) continuously removing CH3CN as it is formed
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54
The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and rxn = + 55 kJ/mol. What is the activation energy for the reverse reaction?

A) 27 kJ/mol
B) 47 kJ/mol
C) 55 kJ/mol
D) 102 kJ/mol
E) More information is needed, since this is a Hess's law calculation.
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55
Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H+ + H2O2 <strong>Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution. H<sup>+ </sup> + H<sub>2</sub>O<sub>2</sub>   H<sub>2</sub>O<sup>+</sup>-OH (rapid equilibrium) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> <font face=symbol></font> HOBr + H<sub>2</sub>O (slow) HOBr + H<sup>+</sup> + Br<sup>-</sup> <font face=symbol></font> Br<sub>2 </sub>+ H<sub>2</sub>O (fast) What is the overall reaction equation for this process?</strong> A) 2H<sub>2</sub>O<sup>+</sup>-OH + 2Br<sup>- </sup> <font face=symbol></font> H<sub>2</sub>O<sub>2 </sub>+ Br<sub>2 </sub>+ 2H<sub>2</sub>O B) 2H<sup>+</sup> + 2Br<sup>-</sup> + H<sub>2</sub>O<sub>2 </sub><font face=symbol></font> Br<sub>2 </sub>+ 2H<sub>2</sub>O C) 2H<sup>+</sup> + H<sub>2</sub>O<sub>2 </sub>+ Br<sup>-</sup> + HOBr <font face=symbol></font> H<sub>2</sub>O<sup>+</sup>-OH + Br<sub>2 </sub>+ H<sub>2</sub>O D) H<sub>2</sub>O<sup>+</sup>-OH + Br<sup>-</sup> + H<sup>+</sup> <font face=symbol></font> Br<sub>2 </sub>+ H<sub>2</sub>O E) none of the above H2O+-OH (rapid equilibrium)
H2O+-OH + Br- HOBr + H2O (slow)
HOBr + H+ + Br- Br2 + H2O (fast)
What is the overall reaction equation for this process?

A) 2H2O+-OH + 2Br- H2O2 + Br2 + 2H2O
B) 2H+ + 2Br- + H2O2 Br2 + 2H2O
C) 2H+ + H2O2 + Br- + HOBr H2O+-OH + Br2 + H2O
D) H2O+-OH + Br- + H+ Br2 + H2O
E) none of the above
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56
In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time. In the gas phase at 500.°C, cyclopropane reacts to form propene in a first-order reaction. The figure shows the natural logarithm of the concentration of cyclopropane (in mol/L) plotted versus time.   a. Explain how this plot confirms that the reaction is first order. b. Calculate the first-order rate constant, k. c. Determine the initial concentration of cyclopropane in this experiment. a. Explain how this plot confirms that the reaction is first order.
b. Calculate the first-order rate constant, k.
c. Determine the initial concentration of
cyclopropane in this experiment.
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57
When a catalyst is added to a reaction mixture, it

A) increases the rate of collisions between reactant molecules.
B) provides reactant molecules with more energy.
C) slows down the rate of the back reaction.
D) provides a new pathway (mechanism) for the reaction.
E) does none of the above.
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58
A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased from 200.°C to 220.°C, the rate constant will increase by a factor of

A) 1.1.
B) 4.3 × 104.
C) 3.2.
D) 7.5.
E) none of the above.
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59
You are studying the rate of the reaction 2A B and have obtained measurements of the concentration of A at times t = 100, 200, 300, ......, 1000 seconds from the start of the reaction. Carefully describe how you would plot a graph and use it to
a. prove that the reaction is second-order with respect to A.
b. determine the second-order rate constant k.
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60
In an exothermic reaction,

A) the forward reaction is slower than the reverse reaction.
B) the reaction rate will speed up with time.
C) the collision energy of the reactants will be greater than that of the products.
D) the forward reaction will have a lower activation energy than the reverse reaction.
E) the activation energy will change as the reaction progresses.
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61
Briefly list the features/properties common to all catalysts and how they work. Draw a labeled reaction energy diagram as part of your answer.
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62
The units of the rate of reaction depend on the order of the reaction.
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63
The greater the energy of activation, Ea, the faster will be the reaction.
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64
At 25.0°C, a rate constant has the value 5.21 × 10-8 L mol-1 s-1. If the activation energy is 75.2 kJ/mol, calculate the rate constant when the temperature is 50.0°C.
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65
The half-life of a second-order reaction does not depend on the initial concentration of reactant.
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66
The rate law cannot be predicted from the stoichiometry of a reaction.
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67
In the collision theory of reaction rates, the rate constant for a bimolecular reaction can be written as
k = zpexp(-Ea/RT)
In one sentence each, clearly explain the physical meaning (interpretation) of the following three factors which appear in the above expression:
a. z
b. p
c. exp(-Ea/RT)
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68
For each of the following terms/concepts, give a brief explanation or definition. Where possible, use examples.
a. order of a reaction
b. elementary reaction
c. reaction intermediate
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69
According to the collision theory of reaction rates, what are the three requirements which must be met before an elementary reaction between two molecules can occur?
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70
The half-life of a first-order reaction does not depend on the initial concentration of reactant.
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71
Briefly outline the key arguments in the collision theory of reaction rates for the elementary reaction
C + D products
Show that this theory predicts a second-order rate law, and how it predicts the form of the rate constant k.
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72
The elementary reaction HBr(g) + Br(g) H(g) + Br2(g) is endothermic.
a. Would you expect the rate constant for the back reaction to be smaller or larger than that for the forward reaction? Explain, briefly.
b. Draw a fully-labeled reaction energy diagram for this reaction, showing the locations of the reactants, products, and transition state.
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73
Is a bimolecular reaction necessarily second-order? Is a second-order reaction necessarily bimolecular? Answer, with explanations and clarifications.
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74
A chemical reaction of the general type
A 2B
is first-order, with a rate constant of 1.52 × 10-4 s-1.
a. Calculate the half-life of A.
b. Assuming the initial concentration of A is 0.067 mol L-1, calculate the time needed for the concentration to fall to 0.010 mol L-1.
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75
You are required to determine the energy of activation (Ea) of a reaction. Briefly describe the experimental measurements you would make and how you would obtain the activation energy from a suitable linear plot of the experimental data.
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76
Cyclobutane decomposes to ethene in a first-order reaction. From measurements of the rate constant (k) at various absolute temperatures (T), the accompanying Arrhenius plot was obtained (ln k versus 1/T). Cyclobutane decomposes to ethene in a first-order reaction. From measurements of the rate constant (k) at various absolute temperatures (T), the accompanying Arrhenius plot was obtained (ln k versus 1/T).   a. Calculate the energy of activation, E<sub>a</sub>. b. Determine the value of the rate constant at 740. K. (In the plot, the units of k are s<sup>-1</sup>.) a. Calculate the energy of activation, Ea.
b. Determine the value of the rate constant at 740. K. (In the plot, the units of k are s-1.)
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77
An elementary reaction is a simple, one-step process.
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78
The gas-phase conversion of 1,3-butadiene to 1,5-cyclooctadiene, 2C4H6 C8H12 was studied, providing data for the plot shown, of 1/[butadiene] versus time. The gas-phase conversion of 1,3-butadiene to 1,5-cyclooctadiene, 2C<sub>4</sub>H<sub>6</sub> <font face=symbol></font> C<sub>8</sub>H<sub>12</sub> was studied, providing data for the plot shown, of 1/[butadiene] versus time.   a. Explain how this plot confirms that the reaction is second order. b. Calculate the second-order rate constant, k. c. Determine the initial concentration of 1,3-butadiene in this experiment. a. Explain how this plot confirms that the reaction is second order.
b. Calculate the second-order rate constant, k.
c. Determine the initial concentration of 1,3-butadiene in this experiment.
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79
All second-order reactions are bimolecular reactions.
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80
The units of the rate constant depend on the order of the reaction.
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