Deck 9: Energy, Enthalpy, and Thermochemistry

Question 1

C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l), ΔH = -1.37 × 10³ kJ
For the combustion of ethyl alcohol as described in the above equation, which of the following statements is(are) true?
I. The reaction is exothermic.
II. The enthalpy change would be different if gaseous water were produced.
III. The reaction is not an oxidation-reduction one.
IV. The products of the reaction occupy a larger volume than the reactants.

A) I, II
B) I, III, IV
C) I only
D) III, IV
E) I, II, III

Answer 1

I, II

Question 2

Calculate ΔE for a system that releases 32 J of heat while 69 J of work is done by it.

A) 32 J
B) 101 J
C) -101 J
D) 37 J
E) -37 J

Answer 2

-101 J

Question 3

Which one of the following statements is false?

A) If q_p for a process is negative, the process is exothermic.
B) A bomb calorimeter measures ΔH directly.
C) The change in enthalpy, ΔH, for a process is equal to the amount of heat absorbed at constant pressure, q_p.
D) The freezing of water is an example of an exothermic reaction.
E) The change in internal energy, ΔE, for a process is equal to the amount of heat absorbed at constant volume, q_v.

Answer 3

A bomb calorimeter measures ΔH directly.

Question 4

Calculate the work for the expansion of an ideal gas from 2.6 to 6.0 L against a pressure of 2.0 atm at constant temperature.

A) 0
B) -1.7 L•atm
C) 6.8 L•atm
D) 4.3 L•atm
E) -6.8 L•atm

Question 5

Which of the following are state functions?

A) work, heat, enthalpy
B) heat, enthalpy, energy
C) enthalpy, energy
D) work, heat, enthalpy, energy
E) work, heat

Question 6

One mole of an ideal gas is expanded from a volume of 1.00 L to a volume of 10.18 L against a constant external pressure of 1.07 atm. Calculate the work. (1 L•atm = 101.3 J)

A) -9.82J
B) -0.0970 J
C) 9.95 J
D) -9.30 × 10² J
E) -9.95× 10² J

Question 7

A gas releases 2.0 J of heat and then performs 11.8 J of work. What is the change in internal energy of the gas?

A) -13.8 J
B) 9.8 J
C) -9.8 J
D) 2.0 J
E) 13.8 J

Question 8

Consider the reaction
C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l), ΔH = -1.37 × 10³ kJ
When a 15.7-g sample of ethyl alcohol (molar mass = 46.1 g/mol) is burned, how much energy is released as heat?

A) 87.3 kJ
B) 4.67× 10² kJ
C) 4.02 × 10³ kJ
D) 4.78 kJ
E) 2.15 × 10⁴ kJ

Question 9

The total volume of hydrogen gas needed to fill the Hindenburg was 2.00 × 10⁸ L at 1.00 atm and 25.0°C. How much energy was evolved when it burned?
H₂(g) + (1/2)O₂(g) → H₂O(l), ΔH = -286 kJ

A) 8.18 × 10⁶ kJ
B) 3.5 × 10¹¹ kJ
C) 2.86 × 10⁴ kJ
D) 5.72 × 10¹⁰ kJ
E) 2.34 × 10⁹ kJ

Question 10

Suppose you add 45 J of heat to a system, let it do 10. J of expansion work, and then return the system to its initial state by cooling and compression. Which statement is true for this process?

A) ΔH < ΔE
B) ΔH = 70. J
C) The work done in compressing the system must exactly equal the work done by the system in the expansion step.
D) The change in the internal energy for this process is zero.

Question 11

Consider the following reaction:
2SO₂(g) + O₂(g) → 2SO₃(g) ΔH = -198.2 kJ
​
Is the reaction endothermic or exothermic as written?

A) It is endothermic.
B) It is exothermic.
C) This can't be determined without more information.

Question 12

The ΔH value for the reaction (1/2)O₂(g) + Hg(l) → HgO(s) is -90.8 kJ. How much heat is released when 31.9g of Hg is reacted with oxygen?

A) 13.4 kJ
B) 90.8 kJ
C) 571 kJ
D) 14.4 kJ
E) 2.90× 10³ kJ

Question 13

For a particular process q = -10 kJ and w = 25 kJ. Which of the following statements is true?

A) The system does work on the surroundings.
B) Heat flows from the surroundings to the system.
C) ΔE = -35 kJ
D) All of these are true.
E) None of these is true.

Question 14

Consider a gas in a 1.0-L bulb at STP that is connected via a valve to another bulb that is initially evacuated. Answer the following questions about what occurs when the valve between the two bulbs is opened.
What is true about the value of q?

A) It is equal to zero.
B) It is greater than zero.
C) It is less than zero.

Question 15

For the reaction H₂O(l) → H₂O(g) at 298 K, 1.0 atm, ΔH is more positive than ΔE by 2.5 kJ/mol. This quantity of energy can be considered to be

A) the heat flow required to maintain a constant temperature.
B) the work done in pushing back the atmosphere.
C) the value of ΔH itself.
D) the difference in the H-O bond energy in H₂O(l) compared to H₂O(g).
E) none of these

Question 16

Given the equation S(s) + O₂(g) → SO₂(g), ΔH = -296 kJ, which of the following statements is(are) true?
I. The reaction is exothermic.
II. When 0.500 mol of sulfur is reacted, 148 kJ of energy is released.
III. When 32.0 g of sulfur is burned, 2.96 × 10⁵ J of energy is released.

A) I and III are true.
B) Only II is true.
C) All are true.
D) I and II are true.
E) None is true.

Question 17

Which of the following statements is(are) true?

A) In exothermic reactions, the reactants are lower in potential energy than the products.
B) The heat of reaction and change in enthalpy can always be used interchangeably.
C) Enthalpy is a state function.
D) A chemist takes the point of view of the surroundings when determining the sign for work or heat.
E) At least two of these statements are true.

Question 18

CH₄ + 4Cl₂(g) → CCl₄(g) + 4HCl(g), ΔH = -434 kJ
Based on the above reaction, what energy change occurs when 1.7 mol of methane reacts?

A) 2.6 × 10⁵ J is released.
B) 7.4 × 10⁵ J is released.
C) 2.6 × 10⁵ J is absorbed.
D) 7.4 × 10⁵ J is absorbed.
E) 4.3 × 10² J is released.

Question 19

Consider the following reaction:
2SO₂(g) + O₂(g) → 2SO₃(g) ΔH = -198 kJ
Calculate the energy change associated with 21.0 g of SO₂ reacting with excess O₂.

A) -64.9 kJ
B) -4.16× 10³ kJ
C) -32.4 kJ
D) -130 kJ
E) -198 kJ

Question 20

Which of the following statements is correct?

A) The system does work on the surroundings when an ideal gas expands against a constant external pressure.
B) The internal energy of a system increases when more work is done by the system than heat is flowing into the system.
C) The internal energy of a system decreases when work is done on the system and heat is flowing into the system.
D) All the statements are true.
E) All the statements are false.

Question 21

Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is changed to 2.0 L while the pressure is kept constant, and then the pressure is increased to 2.00 atm while the volume remains constant. In the second sample, the opposite is done. The pressure is increased first, with constant volume, and then the volume is increased under constant pressure.
Calculate the difference in q between the first sample and the second sample.

A) 1.00 L•atm
B) -2.00 L•atm
C) 2.00 L•atm
D) -1.00 L•atm
E) none of these

Question 22

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate w_AC.

A) 0
B) 30 L•atm
C) -30 L•atm
D) 90 L•atm
E) -90 L•atm

Question 23

Consider a gas in a 1.0-L bulb at STP that is connected via a valve to another bulb that is initially evacuated. Answer the following questions about what occurs when the valve between the two bulbs is opened.
What is true about the value of ΔH?

A) It is greater than zero.
B) It is less than zero.
C) It is equal to zero.

Question 24

If 5.0 kJ of energy is added to a 15.5-g sample of water at 10.°C, the water is

A) completely vaporized.
B) frozen solid.
C) boiling.
D) decomposed.
E) still a liquid.

Question 25

You take 323 g of a solid (melting point = 56.4°C, heat of fusion = 343 J/g) and let it melt in 758 g of water. The water temperature decreases from its initial temperature to 56.4°C. Calculate the initial temperature of the water.

A) 91.4°C
B) 100.0°C
C) 21.4°C
D) 202.6°C
E) 249.0°C

Question 26

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate ΔH_ABD.

A) -475 L•atm
B) -25 L•atm
C) 475 L•atm
D) 25 L•atm
E) none of these

Question 27

Consider a gas in a 1.0-L bulb at STP that is connected via a valve to another bulb that is initially evacuated. Answer the following questions about what occurs when the valve between the two bulbs is opened.
What is true about the value of w?

A) It is less than zero.
B) It is equal to zero.
C) It is greater than zero.

Question 28

Which statement is true of a process in which 1 mol of a gas is expanded from state A to state B?

A) The final volume of the gas will depend on the path taken.
B) The amount of work done in the process must be the same, regardless of the path.
C) When the gas expands from state A to state B, the surroundings are doing work on the system.
D) The amount of heat released in the process will depend on the path taken.
E) It is not possible to have more than one path for a change of state.

Question 29

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate q_AB.

A) 135 L•atm
B) -135 L•atm
C) 225 L•atm
D) -225 L•atm
E) none of these

Question 30

For the vaporization of water at 1.00 atm,
ΔH = 43.54 kJ/mol at 298 K and ΔH = 40.68 kJ/mol at 373 K
The constant-pressure heat capacity of liquid water is 75.3 J/mol • K. Calculate the constant-pressure heat capacity for H₂O(g).

A) 20.8 J/mol•K
B) 2790 J/mol•K
C) 75.3 J/mol•K
D) 37.2 J/mol•K
E) none of these

Question 31

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate ΔH_ACD.

A) -175 L•atm
B) 175 L•atm
C) -25 L•atm
D) 25 L•atm
E) none of these

Question 32

Consider a gas in a 1.0-L bulb at STP that is connected via a valve to another bulb that is initially evacuated. Answer the following questions about what occurs when the valve between the two bulbs is opened.
What is true about the value of ΔE?

A) It is less than zero.
B) It is greater than zero.
C) It is equal to zero.

Question 33

Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is changed to 2.0 L while the pressure is kept constant, and then the pressure is increased to 2.00 atm while the volume remains constant. In the second sample, the opposite is done. The pressure is increased first, with constant volume, and then the volume is increased under constant pressure.
Calculate the difference in ΔE between the first sample and the second sample.

A) 0
B) 1.00 L•atm
C) 2.00 L•atm
D) 4.50 L•atm
E) none of these

Question 34

Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is changed to 2.0 L while the pressure is kept constant, and then the pressure is increased to 2.00 atm while the volume remains constant. In the second sample, the opposite is done. The pressure is increased first, with constant volume, and then the volume is increased under constant pressure.
Calculate the difference in w between the first sample and the second sample.

A) -2.00 L•atm
B) 1.00 L•atm
C) 2.00 L•atm
D) -1.00 L•atm
E) none of these

Question 35

A calorimeter contains 124 g of water at 26.6°C. A block of metal with a mass of 26 g is heated to 95.8°C and then placed in the water in the calorimeter. After sufficient time, the temperature of the water is measured and found to be 29.0°C. Calculate the heat capacity per gram of metal. Assume no heat is lost to the calorimeter or the surroundings.

A) 0.17 J/g°C
B) 5.5 × 10² J/g°C
C) 0.031 J/g°C
D) 1.4 J/g°C
E) 0.72 J/g°C

Question 36

A 25.0 g piece of aluminum (which has a molar heat capacity of 24.03 J/mol°C) is heated to 86.4°C and dropped into a calorimeter containing water (the specific heat capacity of water is 4.18 J/g°C) initially at 21.1°C. The final temperature of the water is 26.8°C. Calculate the mass of water in the calorimeter.

A) 5.6 × 10¹ g
B) 1.5× 10³ g
C) 0.51 g
D) 1.7 g
E) 6.1 × 10¹ g

Question 37

Two metals of equal mass with different heat capacities are subjected to the same amount of heat. Which undergoes the smaller change in temperature?

A) To determine this, you need to know which metals you are talking about.
B) Both undergo the same change in temperature.
C) The metal with the higher heat capacity.
D) The metal with the lower heat capacity.
E) To determine this, you need to know the initial temperatures of the metals.

Question 38

When 0.157 mol of NH₃ is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is ΔH for this reaction per mole of NH₃ consumed?

A) -22.7 J
B) -44.0 kJ
C) +44.0 kJ
D) -1.08 kJ
E) +22.7 J

Question 39

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate w_AB.

A) 0
B) 90 L•atm
C) -90 L•atm
D) -30 L•atm
E) 30 L•atm

Question 40

Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following two different pathways. The first pathway is A (3.00 atm, 20.0 L) to C (1.00 atm, 20.0 L) to D (1.00 atm, 50.0 L); and the second pathway is A (3.00 atm, 20.0 L) to B (3.00 atm, 50.0 L) to D (1.00 atm, 50.0 L). In each case, the gas is taken from state A to state D.
Calculate q_AC.

A) 60 L•atm
B) 100 L•atm
C) -60 L•atm
D) -100 L•atm
E) none of these

Question 41

A calorimeter contains 95 g of water at 25.0°C. A 5.0-g sample of ice (at -5.0°C) is added to the water in the calorimeter, and eventually all of the ice melts. Calculate the final temperature of the water. Assume no heat is lost to the calorimeter or the surroundings.

A) 20.7°C
B) 21.2°C
C) 17.5°C
D) 19.6°C
E) none

Question 42

A bomb calorimeter has a heat capacity of 2.10 kJ/K. When a 0.196 g sample of gas with a molar mass of 28.0 g/mol was burned in this calorimeter, the temperature increased by 2.15 K. Calculate the energy of combustion for 1 mol of this gas.

A) -4.52 kJ
B) -0.0316 kJ
C) -6.45 × 10² kJ
D) -1.26 × 10² kJ
E) -2.30 × 10¹ kJ

Question 43

Use the following table: Calculate ΔH° for the reaction
P₄O₁₀(g) + 6PCl₅(g) → 10Cl₃PO(g)

A) -610.1 kJ
B) -2682.2 kJ
C) -7555.0 kJ
D) -110.5 kJ
E) None of these is within 5% of the correct answer.

Question 44

Using Hess's law and equations 1-3 below, find ΔH° at 25°C for the oxidation of C₂H₅OH(l).C₂H₅OH(l) + 3O₂(g) → 3H₂O(l) + 2CO₂(g)
1)C₂H₄(g) + 3O₂(g) → 2CO₂(g) + 2H₂O(l)
ΔH° = -1411 kJ
2)C(graphite) + 3H₂(g) + (1/2)O₂(g) → C₂H₅OH(l)
ΔH° = -278 kJ
3)C₂H₄(g) + H₂O(l) → C₂H₅OH(l)
ΔH° = -44 kJ

A) -1367 kJ
B) 44 kJ
C) 632 kJ
D) -1742 kJ
E) none of these

Question 45

When a student performs an endothermic reaction in a calorimeter, how (if any) does the calculated value of ΔH differ from the actual value if the heat exchanged with the calorimeter is not taken into account?

A) ΔH_calc is less positive because the reaction absorbs heat from the calorimeter.
B) ΔH_calc equals the actual value because the calorimeter does not absorb heat.
C) ΔH_calc is more negative because the calorimeter always absorbs heat from the reaction.
D) ΔH_calc is less negative because the calorimeter absorbs heat from the reaction.
E) ΔH_calc is more positive because the reaction absorbs heat from the calorimeter.

Question 46

At 25°C, the following heats of reaction are known: At the same temperature, calculate ΔH for the following reaction:

A) -217.5 kJ/mol
B) -108.7 kJ/mol
C) +217.5 kJ/mol
D) -130.2 kJ/mol
E) none of these

Question 47

One mole of a liquid is vaporized at its boiling point, 65°C and 1.00 atm. ΔH_vap for the liquid is 43.8 kJ/mol at 65° C.
Calculate w.

A) -27.7 J
B) 27.7 J
C) 2.81 × 10³ J
D) -2.81 × 10³ J
E) none of these

Question 48

One mole of a liquid is vaporized at its boiling point, 65°C and 1.00 atm. ΔH_vap for the liquid is 43.8 kJ/mol at 65° C.
Calculate ΔE.

A) 71.5 kJ
B) 16.1 kJ
C) 41.0 kJ
D) 46.6 kJ
E) none of these

Question 49

Calculate ΔH° for the reaction C₄H₄(g) + 2H₂(g) → C₄H₈(g), using the following data:
ΔH°_combustion for C₄H₄(g) = -2341 kJ/mol
ΔH°_combustion for H₂(g) = -286 kJ/mol
ΔH°_combustion for C₄H₈(g) = -2755 kJ/mol

A) -128 kJ
B) 158 kJ
C) -158 kJ
D) 128 kJ
E) none of these

Question 50

The standard enthalpy of formation of H₂O(l) at 298 K is -285.6 kJ/mol. Calculate the change in internal energy for the following process at 298 K:
H₂(g) + 1/2O₂(g) → H₂O(l)

A) -285.6 kJ/mol
B) 283.1 kJ/mol
C) -289.3 kJ/mol
D) -281.9 kJ/mol
E) -283.1 kJ/mol

Question 51

A calorimeter contains 240 g of water at 22.4°C. A block of metal with a mass of 89 g is heated to 97.1°C and then placed in the water in the calorimeter. After sufficient time, the temperature of the water is measured and found to be 26.9°C. Calculate the specific heat capacity per gram of metal. Assume no heat is lost to the calorimeter or the surroundings.

A) 0.10J/g°C
B) 0.024 J/g°C
C) 0.17 J/g°C
D) 0.72 J/g°C
E) 1.4 J/g°C

Question 52

75.0 mL of a pure liquid at 245 K is mixed with 100.0 mL of the same pure liquid at 365. K. What is the final temperature of the mixture?

A) 325 K
B) 295 K
C) 305 K
D) 314 K
E) none of these

Question 53

A calorimeter contains 142 g of water at 22.5°C. A 12 g sample of NaCl is added to the water in the calorimeter. After the solid has dissolved, the temperature of the water is 21.4°C. Calculate the enthalpy of solution for dissolving sodium chloride. Assume that no heat is lost to the calorimeter or the surroundings and that the specific heat of the solution is the same as that of pure water.

A) 0.059 kJ/mol
B) 0.71 kJ/mol
C) 0.83 kJ/mol
D) 3.2 kJ/mol
E) 3.5 kJ/mol

Question 54

A 50.0-g sample of a metal is heated to 98.7°C and then placed in a calorimeter containing 395.0 g of water (c = 4.18 J/g°C) at 22.5°C. The final temperature of the water is 24.5°C. Which metal was used?

A) iron (C = 0.45 J/g°C)
B) lead (C = 0.14 J/g°C)
C) copper (C = 0.20 J/g°C)
D) aluminum (C = 0.89 J/g°C)
E) none of these

Question 55

A 1.00-g sample of the rocket fuel hydrazine, N₂H₄, is burned in a bomb calorimeter containing 1200. g of water. The temperature of the water and the bomb calorimeter rises from 24.62°C to 28.16°C. Assuming the heat capacity of the empty bomb calorimeter is 837 J/°C, calculate the heat of combustion of 1 mol of hydrazine in the bomb calorimeter. (The specific heat capacity of water is 4.184 J/g•°C.)

A) -152 kJ
B) +47.4 kJ
C) +20.7 kJ
D) -665 kJ
E) -569 kJ

Question 56

A 140.0-g sample of water at 25.0°C is mixed with 100.0 g of a certain metal at 100.0°C. After thermal equilibrium is established, the (final) temperature of the mixture is 29.6°C. What is the heat capacity of the metal, assuming it is constant over the temperature range concerned?

A) 0.031 J/g°C
B) 0.38 J/g°C
C) 0.96 J/g°C
D) 0.76 J/g°C
E) none of these

Question 57

Given: Calculate the standard enthalpy of formation of CuO(s).

A) +299 kJ
B) +155 kJ
C) -166 kJ
D) -155 kJ
E) -299 kJ

Question 58

At 25°C, the following heats of reaction are known: At the same temperature, calculate ΔH for the following reaction:

A) -2422kJ
B) -226 kJ
C) 226 kJ
D) 2422 kJ
E) none of these

Question 59

The enthalpy of fusion of ice is 6.020 kJ/mol. The heat capacity of liquid water is 75.4 J/mol °C. What is the smallest number of ice cubes at 0 °C, each containing 1 mol of water, necessary to cool 500. g of liquid water initially at 20 °C to 0 °C?

A) 1
B) 15
C) 7
D) 14
E) 126

Question 60

Consider the following numbered processes:
1) A → 2B
2) B → C + D
3) E → 2D
ΔH for the process A → 2C + E is

A) ΔH₁ + ΔH₂
B) ΔH₁ + 2ΔH₂ - ΔH₃
C) ΔH₁ + ΔH₂ + ΔH₃
D) ΔH₁ + 2ΔH₂ + ΔH₃
E) ΔH₁ + ΔH₂ - ΔH₃

Question 61

Consider the following reaction:
2Al(s) + 3Cl₂(g) → 2AlCl₃(s), ΔH = -1390.81 kJ

A) Is the reaction exothermic or endothermic?
B) Calculate the heat produced when 10.0 g of AlCl₃ forms.
C) How many grams of Al are required to produce 1.00 kJ of energy?

Question 62

The heat combustion of acetylene, C₂H₂(g), at 25°C, is -1299 kJ/mol. At this temperature, ΔH°_f values for CO₂(g) and H₂O(l) are -393 and -286 kJ/mol, respectively. Calculate ΔH°_f for acetylene.

A) 227 kJ/mol
B) -625 kJ/mol
C) 625 kJ/mol
D) 2376 kJ/mol
E) none of these

Question 63

Consider the following data:
Use Hess's law to find the change in enthalpy at 25°C for the following equation:
CaC₂(s) + 2H₂O(l) → C₂H₂(g) + Ca(OH)₂(aq)

Question 64

Acetylene (C₂H₂) and butane (C₄H₁₀) are gaseous fuels. Determine the ratio of energy available from the combustion of a given volume of acetylene to butane at the same temperature and pressure using the following data:
The change in enthalpy of combustion for C₂H₂(g) = -49.9 kJ/g.The change in enthalpy of combustion for C₄H₁₀ = -49.5 kJ/g.

Question 65

The standard state of carbon as a free element is graphite. C₆₀ is an allotropic form of carbon belonging to a class of structures known as fullerenes. for C₆₀ should be

A) zero
B) positive
C) negative
D) equal to for the other allotropic forms of carbon
E) A and D

Question 66

For which of the following reaction(s) is the enthalpy change for the reaction not equal to ΔH°_f of the product?
I. 2H(g) → H₂(g)
II. H₂(g) + O₂(g) → H₂O₂(l)
III. H₂O(l) + O(g) → H₂O₂(l)

A) I and III
B) III only
C) II and III
D) II only
E) I only

Question 67

The standard enthalpy change for the following reaction is -542 kJ:
H₂(g) + F₂(g) → 2HF(g)
Calculate the standard enthalpy of formation of hydrogen fluoride.

A) -1084 kJ/mol
B) 542 kJ/mol
C) -542 kJ/mol
D) -271 kJ/mol
E) none of these

Question 68

Which of the following statements is true for a monatomic ideal gas?

A) C_v C_p
B) C_v C_p
C) C_v = C_p + R
D) C_p = R
E) C_v is temperature dependent

Question 69

Using the information below, calculate ΔH°_f for C₂H₅OH(l).C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l), ΔH° = -1367 kJ
ΔH°_f for CO₂(g) = -393.5 kJ/mol
ΔH°_f for H₂O(l) = -286 kJ/mol

A) 278 kJ/mol
B) -688 kJ/mol
C) -3.01× 10³ kJ/mol
D) 688kJ/mol
E) -278 kJ/mol

Question 70

Consider the following standard heats of formation:
P₄O₁₀(s) = -3110 kJ/mol
H₂O(l) = -286 kJ/mol
H₃PO₄(s) = -1279 kJ/mol
Calculate the change in enthalpy for the following process:
P₄O₁₀(s) + 6H₂O(l) → 4H₃PO₄(s)

Question 71

The heat of formation of Fe₂O₃(s) is -826 kJ/mol. Calculate the heat of the reaction 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s) when a 15.2 g sample of iron is reacted.

A) -450 kJ
B) -113 kJ
C) -78.7 kJ
D) - 826 kJ
E) -225 kJ

Question 72

The combustion of methanol takes place according to the reaction
2CH₃OH(l) + 3O₂(g) → 2CO₂(g) + 4H₂O(l)
Calculate ΔH for the combustion of 1 mol of methanol under standard conditions. Use the following standard enthalpies of formation:

A) -1452.4 kJ/mol
B) +1452.4 kJ/mol
C) -726.2 kJ/mol
D) +726.2 kJ/mol
E) none of these

Question 73

Using the following data, calculate the standard heat of formation of ICl(g) in kJ/mol.

A) 16.8 kJ/mol
B) -211 kJ/mol
C) 245 kJ/mol
D) -14.6 kJ/mol
E) 439 kJ/mol

Question 74

Standard enthalpies of formation are tabulated on a

A) volume basis.
B) mass basis.
C) pressure basis.
D) mole basis.

Question 75

For the reaction
AgI(s) + (1/2)Br₂(g) → AgBr(s) + (1/2)I₂(s), ΔH° = -54.0 kJ
ΔH°_f for AgBr(s) = -100.4 kJ/mol
ΔH°_f for Br₂(g) = +30.9 kJ/mol
The value of ΔH°_f for AgI(s) is

A) +61.8 kJ/mol
B) -77.3 kJ/mol
C) -61.8 kJ/mol
D) -123.5 kJ/mol
E) +77.3 kJ/mol

Question 76

Given the following two reactions at 298 K and 1 atm, which of the statements is true?

A) ΔH_f for NO₂(g) = ΔH₂ + (1/2)ΔH₁
B) ΔH₁ = ΔH₂
C) ΔH_f for NO(g) = ΔH₁
D) ΔH_f for NO₂(g) = ΔH₂
E) none of these

Question 77

Using the information below, calculate ΔH°_f for PbO(s).PbO(s) + CO(g) → Pb(s) + CO₂(g), ΔH° = -131.4 kJ
ΔH°_f for CO₂(g) = -393.5 kJ/mol
ΔH°_f for CO(g) = -110.5 kJ/mol

A) +283.0 kJ/mol
B) +252.1 kJ/mol
C) -151.6 kJ/mol
D) -283.0 kJ/mol
E) -372.6 kJ/mol

Question 78

The enthalpy of formation of an element in its standard state is

A) zero.
B) the enthalpy of its reaction with oxygen.
C) the enthalpy of its reaction with hydrogen.
D) determined by its melting point.
E) none of these

Question 79

Specific heat capacities are tabulated on a

A) mass basis.
B) volume basis.
C) pressure basis.
D) mole basis.

Question 80

Choose the correct equation for the standard enthalpy of formation of CO(g), where ΔH°_f for CO = -110.5 kJ/mol.

A) C_graphite(s) + CO₂(g) → 2CO(g), ΔH° = -110.5 kJ
B) C_graphite(s) + O(g) → CO(g), ΔH° = -110.5 kJ
C) 2C_graphite(s) + O₂(g) → 2CO(g), ΔH° = -110.5 kJ
D) , ΔH° = -110.5 kJ
E) CO(g) → C_graphite(s) + O(g), ΔH° = -110.5 kJ