Deck 8: Thermochemistry

Question 1

The combustion of benzoic acid,C₇H₆O₂,can be used to determine the heat capacity of a bomb calorimeter.The heat evolved per mole of benzoic acid combusted is 3.09 × 10³ kJ.If the combustion of 1.000 g of benzoic acid increases the temperature of a calorimeter by 7.53°C.What is the heat capacity of the calorimeter?

A) 1.36 kJ/°C
B) 3.36 kJ/°C
C) 4.10 kJ/°C
D) 51.3 kJ/°C
E) 191 kJ/°C

Answer 1

3.36 kJ/°C

Question 2

All of the following statements are true EXCEPT

A) the value of q is negative in an endothermic process.
B) heat flows from the system into the surroundings in an exothermic process.
C) the value of q is positive when heat flows into a system from the surroundings.
D) enthalpy is a state property.
E) in an endothermic process heat flows from the surroundings into the system.

Answer 2

the value of q is negative in an endothermic process.

Question 3

If 50.0 g of benzene,C₆H₆,at 25.0°C absorbs 2.71 kJ of energy in the form of heat,what is the final temperature of the benzene? The specific heat of benzene is 1.72 J/g⋅°C.

A) 25.0°C
B) 31.5°C
C) 56.5°C
D) 32.3°C
E) 57.3°C

Answer 3

56.5°C

Question 4

If 495 J is required to change the temperature of 12.7 g of sodium chloride from 75.0°C to 135°C,what is the specific heat of sodium chloride?

A) 0.866 J/g⋅°C
B) 2.60 J/g⋅°C
C) 0.650 J/g⋅°C
D) 1.15 J/g⋅°C
E) 2.83 × 10⁵ J/g⋅°C

Question 5

When 1.75 g of CaCl₂ dissolves in 125 g of water in a coffee-cup calorimeter,the temperature increases by 2.44°C.What is the heat change per mole of CaCl₂ dissolved in water? Assume that all the heat is absorbed by the water (c = 4.18 J/g⋅°C).

A) −11.3 kJ
B) −728 J
C) −1.13 kJ
D) −80.9 kJ
E) −91.9 kJ

Question 6

How many joules are equivalent to 1.50 × 10³ calories?

A) 1.50 × 106 J
B) 3.59 × 10² J
C) 6.28 × 10³ J
D) 3.59 × 10⁵ J
E) 6.28 × 10⁶ J

Question 7

Water has a specific heat of 4.18 J/g⋅°C.If 35.0 g of water at 98.8°C loses 4.94 kJ of heat,what is the final temperature of the water?

A) 32.0°C
B) 46.2°C
C) 47.2°C
D) 57.2°C
E) 65.0°C

Question 8

Isooctane is a primary component of gasoline and gives gasoline its octane rating.Burning 1.00 mL of isooctane (d = 0.688g/mL)releases 33.0 kJ of heat.When 10.0 mL of isooctane is burned in a bomb calorimeter,the temperature in the bomb increases from 23.2°C to 66.5°C.What is the heat capacity of the bomb calorimeter?

A) 11.2 kJ/°C
B) −3.68 kJ/°C
C) −7.62 kJ/°C
D) 3.68 kJ/°C
E) 7.62 kJ/°C

Question 9

Acetylene,C₂H₂,is a gas used in welding.The molar enthalpy of combustion for acetylene is -2599 kJ.A mass of 0.338 g C₂H₂(g)is combusted in a bomb calorimeter.If the heat capacity of the calorimeter is 5.54 kJ/°C,what is the temperature increase of the bomb calorimeter?

A) 1.59°C
B) 6.09°C
C) 7.01°C
D) 12.3°C
E) 18.0°C

Question 10

A coffee-cup calorimeter contains 10.0 g of water at 59.00°C.If 3.00 g gold at 15.20°C is placed in the calorimeter,what is the final temperature of the water in the calorimeter? The specific heat of water is 4.18 J/g⋅°C;the specific heat of gold is 0.128 J/g⋅°C.

A) 55.37°C
B) 58.60°C
C) 59.40°C
D) 60.80°C
E) 64.19°C

Question 11

Specific heat (c)is defined as

A) the quantity of heat needed to change the temperature of 1.00 g of a substance by 1°C.
B) the quantity of heat needed to change the temperature of 1.00 g of a substance by 4.184°C.
C) the capacity of a substance to gain or lose 1.00 J of energy in the form of heat.
D) the temperature change undergone when 1.00 g of a substance absorbs 4.184 J.
E) the maximum amount of energy in the form of heat that 1.00 g of a substance may absorb without decomposing.

Question 12

When 10.0 g KOH is dissolved in 100.0 g of water in a coffee-cup calorimeter,the temperature rises from 25.18 °C to 47.53 °C.What is the enthalpy change per gram of KOH dissolved in the water? Assume that the solution has a specific heat capacity of 4.18 J/g⋅K.

A) -116 J/g
B) -934 J/g
C) -1.03 × 10³ J/g
D) -2.19 × 10³ J/g
E) -1.03 × 10⁴ J/g

Question 13

When 66.0 g of an unknown metal at 28.5°C is placed in 83.0 g H₂O at 78.5°C,the water temperature decreases to 75.9°C.What is the specific heat capacity of the metal? The specific heat capacity of water is 4.184 J/g⋅°C.

A) 0.055 J/g⋅°C
B) 0.29 J/g⋅°C
C) 0.69 J/g⋅°C
D) 0.18 J/g⋅°C
E) 2.6 J/g⋅°C

Question 14

TThe heat capacity of iron is 0.446 J/°C.How much heat is required to change the temperature of 5.00 grams of iron by 50.0°C?

A) 0.223 J
B) 22.3 J
C) 112 J
D) 558 J
E) 612 J

Question 15

A coffee-cup calorimeter contains 50.0 g of water at 60.51°C.A 12.4 g piece of graphite at 24.21°C is placed in the calorimeter.The final temperature of the water and the carbon is 59.02°C.Calculate the specific heat of carbon.The specific heat of water is 4.18 J/g⋅°C.

A) 0.328 J/g⋅°C
B) 0.639 J/g⋅°C
C) 0.692 J/g⋅°C
D) 0.721 J/g⋅°C
E) 1.39 J/g⋅°C

Question 16

Commercial cold packs consist of solid ammonium nitrate and water.NH₄NO₃ absorbs 25.69 kJ of heat per mole dissolved in water.In a coffee-cup calorimeter,5.60 g NH₄NO₃ is dissolved in 100.0 g of water at 22.0°C.What is the final temperature of the solution? Assume that the solution has a specific heat capacity of 4.18 J/g⋅°C.

A) 0.0°C
B) 17.9°C
C) 11.6°C
D) -54.8°C
E) 26.1°C

Question 17

A chemical reaction in a bomb calorimeter evolves 3.15 kJ of heat.If the temperature of the calorimeter is raised from 19.19°C to 22.03°C,what is the heat capacity of the calorimeter?

A) 1.11 kJ/°C
B) 2.01 kJ/°C
C) 8.95 kJ/°C
D) 14.5 kJ/°C
E) 69.4 kJ/°C

Question 18

Aluminum has a specific heat of 0.902 J/g⋅°C.How many joules of heat are required to change the temperature of 8.50 grams of aluminum from 25.0°C to 93.4°C?

A) 7.67 J
B) 71.7 J
C) 192 J
D) 483 J
E) 524 J

Question 19

Copper has a specific heat of 0.382 J/g⋅°C.The temperature of an unknown mass of copper increases by 4.50°C when it absorbs 3.97 J of heat.What is the mass of the copper?

A) 2.31 g
B) 4.90 g
C) 6.82 g
D) 8.85 g
E) 46.8 g

Question 20

If 35.0 g H₂O at 22.7°C is combined with 65.0 g H₂O at 87.5°C,what is the final temperature of the mixture? The specific heat capacity of water is 4.184 J/g⋅°C.

A) 25.1°C
B) 45.4°C
C) 50.8°C
D) 64.8°C
E) 48.9°C

Question 21

Determine the heat of reaction for the decomposition of one mole of benzene to acetylene, C₆H₆(l)? 3C₂H₂(g)
Given the following thermochemical equations:
$\begin{array}{ll}2 \mathrm{C}_{6} \mathrm{H}_{6}(l)+15 \mathrm{O}_{2}(g) \rightarrow 12 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) & \Delta H=-6271 \mathrm{~kJ} \\2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+5 \mathrm{O}_{2}(g) \rightarrow 4 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g) & \Delta H=-2511 \mathrm{~kJ}\end{array}$

A) 631 kJ
B) 1262 kJ
C) 3760 kJ
D) 6902 kJ
E) 8782 kJ

Question 22

The standard molar enthalpy of formation of NH₃(g)is -45.9 kJ/mol.What is the enthalpy change if 9.51 g N₂(g)and 1.96 g H₂(g)react to produce NH₃(g)?

A) -10.3 kJ
B) -20.7 kJ
C) -29.9 kJ
D) -43.7 kJ
E) -65.6 kJ

Question 23

Determine the heat of reaction for the combustion of sulfur dioxide, 2SO₂(g)+ O₂(g)? 2SO₃(g)
Given the following thermochemical equations:
$\begin{array}{ll}\mathrm{S}_{8}(s)+8 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{2}(g) & \Delta H=-2374.6 \mathrm{~kJ} \\\mathrm{~S}_{8}(s)+12 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{3}(g) & \Delta H=-3165.8 \mathrm{~kJ}\end{array}$

A) ?5540.4 kJ
B) ?1385.1 kJ
C) ?197.8 kJ
D) 251.7 kJ
E) 791.2 kJ

Question 24

Which of the following chemical equations does not correspond to a standard molar enthalpy of formation?

A) Mg(s)+ C(s)+ 3/2O₂(g)→ MgCO₃(s)
B) C(s)+ 1/2O₂(g)→ CO(g)
C) N₂(g)+ O₂(g)→ 2NO(g)
D) N₂(g)+ 2O₂(g)→ N₂O₄(g)
E) H₂(g)+ 1/2O₂(g)→ H₂O(l)

Question 25

Carbon and oxygen react to give carbon dioxide.The reaction of 4.49 g C(s)with 9.21 g O₂(g)releases −113.2 kJ of heat.What is the enthalpy of formation of CO₂(g)?

A) −393 kJ
B) −303 kJ
C) −285.8 kJ
D) −171 kJ
E) −113.2 kJ

Question 26

The molar enthalpies of formation for H₂O(l)and H₂O(g)are −285.8 kJ and −241.8 kJ,respectively.How much heat is released when 25 g of water condenses from the gas to the liquid phase?

A) −2.4 kJ
B) −32 kJ
C) −61 kJ
D) −88 kJ
E) −1100 kJ

Question 27

Determine the heat of evaporation of carbon disulfide, CS₂(l)? CS₂(g)
Given the enthalpies of reaction below.
$\begin{array}{ll}\mathrm{C}(s)+2 \mathrm{~S}(s) \rightarrow \mathrm{CS}_{2}(l) & \Delta H=+89.4 \mathrm{~kJ} \\\mathrm{C}(s)+2 \mathrm{~S}(s) \rightarrow \mathrm{CS}_{2}(g) & \Delta H=+116.7 \mathrm{~kJ}\end{array}$

A) -206.1 kJ
B) -27.3 kJ
C) +27.3 kJ
D) +206.1 kJ
E) +1.31 kJ

Question 28

Iron oxide reacts with aluminum in an exothermic reaction. Fe₂O₃(s)+ 2Al(s)→ 2Fe(s)+ Al₂O₃(s)
The reaction of 5.00 g Fe₂O₃ with excess Al evolves 26.6 kJ of energy in the form of heat.Calculate the enthalpy change per mole of Fe₂O₃ reacted.

A) -5.32 kJ
B) -1.33 × 10² kJ
C) -2.12 × 10⁴ kJ
D) -2.12 × 10² kJ
E) -8.50 × 10² kJ

Question 29

If 25.0 g H₂O at 85.0°C is mixed in a coffee-cup calorimeter with 15.0 g H₂O at 20.0°C,what is the final temperature of the mixture? The specific heat of water is 4.18 J/g⋅°C.

A) 45.6°C
B) 52.5°C
C) 60.6°C
D) 68.4°C
E) 183°C

Question 30

Determine the heat of formation of sulfuric acid,H₂SO₄(l),from the following thermochemical equations: $\begin{array}{ll}\mathrm{S}_{8}(s)+8 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{2}(g) & \Delta H=-2374.6 \mathrm{~kJ} \\\mathrm{~S}_{8}(s)+12 \mathrm{O}_{2}(g) \rightarrow 8 \mathrm{SO}_{3}(g) & \Delta H=-3165.8 \mathrm{~kJ} \\\mathrm{H}_{2} \mathrm{O}(l)+\mathrm{SO}_{3}(g) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{4}(l) & \Delta H=-132.4 \mathrm{~kJ} \\2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) & \Delta H=-571.7 \mathrm{~kJ}\end{array}$

A) ?814.0 kJ
B) ?1099.9 kJ
C) ?2164.7 kJ
D) ?3869.9 kJ
E) ?6244.5 kJ

Question 31

30.0 g H₂O at an unknown temperature is mixed with 27.0 g of water at 15.8°C in a coffee-cup calorimeter.If the final temperature of the mixture is 29.1°C,what is the initial temperature of the water?

A) 23.7°C
B) 31.1°C
C) 39.7°C
D) 41.1°C
E) 46.7°C

Question 32

Methane,CH₄,reacts with oxygen to produce carbon dioxide,water,and heat. CH₄(g)+ 2O₂(g)→ CO₂(g)+ 2H₂O(l)
ΔH = −890.3 kJ
What is the value of ΔH if 5.00 g of CH₄ is combusted?

A) −157 kJ
B) −277 kJ
C) −445 kJ
D) −714 kJ
E) −1.43 × 10⁴ kJ

Question 33

10.0 g of ice at 0.00°C is mixed with 25.0 g of water at 35.00°C in a coffee-cup calorimeter.What is the final temperature of the mixture? The specific heat of water is 4.18 J/g⋅°C;the heat of fusion of water is 333 J/g.

A) 0.00°C
B) 2.24°C
C) 5.22°C
D) 25.0°C
E) 47.8°C

Question 34

Determine the heat of formation of calcium carbonate from the thermochemical equations given below. $\begin{array}{ll}\mathrm{Ca}(\mathrm{OH})_{2}(s) \rightarrow \mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) & \Delta H=65.2 \mathrm{~kJ} \\\mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{CaCO}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) & \Delta H=-113.2 \mathrm{~kJ} \\\mathrm{C}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) & \Delta H=-393.5 \mathrm{~kJ} \\2 \mathrm{Ca}(\mathrm{s})+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CaO}(s) & \Delta H=-1270.2 \mathrm{~kJ}\end{array}$

A) ?178.4 kJ
B) ?493.2 kJ
C) ?828.7 kJ
D) ?980.6 kJ
E) ?1207.0 kJ

Question 35

Determine the heat of reaction for the combustion of ammonia,
4NH3(g) + 7O2(g) ? 4NO2(g) + 6H2O(l) using molar enthalpies of formation.
$\begin{array}{ll}\text { molecule } & \Delta f H^{\circ}(\mathrm{kJ} / \mathrm{mol}) \\\hline \mathrm{NH}_{3}(g) & -45.9 \\\mathrm{NO}_{2}(g) & +33.1 \\\mathrm{H}_{2} \mathrm{O}(l) & -285.8\end{array}$

A) +30.24 kJ
B) -206.9 kJ
C) -298.6 kJ
D) -1398.8 kJ
E) -1663.6 kJ

Question 36

If not handled carefully,ammonium perchlorate can decompose violently according to the thermochemical equation below.
$2 \mathrm{NH}_{4} \mathrm{ClO}_{4}(s) \rightarrow \mathrm{N}_{2}(g)+\mathrm{Cl}_{2}(g)+2 \mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g) \quad\quad\quad\quad\quad \Delta H=-375.6 \mathrm{~kJ}$
The enthalpy of formation of H₂O(g)is ?241.8 kJ.Calculate the enthalpy of formation of ammonium perchlorate.

A) ?295.8 kJ
B) ?156.4 kJ
C) 66.9 kJ
D) 133.8 kJ
E) 561.1 kJ

Question 37

The enthalpy of formation of H₂O(l)is −285.8 kJ/mol.What is the enthalpy change if 1.62 g H₂(g)reacts with 9.21 g O₂(g)to form H₂O(l)?

A) −229 kJ
B) −165 kJ
C) −107 kJ
D) −45.5 kJ
E) −31.0 kJ

Question 38

Determine the heat of reaction for the oxidation of iron, 2Fe(s)+ $\frac{3}{2}$ O₂(g)? Fe₂O₃(s)
Given the following thermochemical equations:
$\begin{array}{ll}2 \mathrm{Fe}(s)+6 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{Fe}(\mathrm{OH})_{3}(s)+3 \mathrm{H}_{2}(g) & \Delta H=321.8 \mathrm{~kJ} \\\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{Fe}(\mathrm{OH})_{3}(s) & \Delta H=288.6 \mathrm{~kJ} \\2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) & \Delta H=-571.7 \mathrm{~kJ}\end{array}$

A) ?1681.9 kJ
B) ?1143.1 kJ
C) ?824.4 kJ
D) 33.2 kJ
E) 38.7 kJ

Question 39

Determine ?H for the following reaction, 2NH₃(g)+ 5/2O₂(g)? 2NO(g)+ 3H₂O(g)
Given the thermochemical equations below.
$\begin{array}{ll}\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{NO}(g) & \Delta H=+180.8 \mathrm{~kJ} \\\mathrm{~N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g) & \Delta H=-91.8 \mathrm{~kJ} \\2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(g) & \Delta H=-483.6 \mathrm{~kJ}\end{array}$

A) -1178.2 kJ
B) -452.8 kJ
C) -394.6 kJ
D) -211.0 kJ
E) +1178.2 kJ

Question 40

All of the following statements are true EXCEPT

A) Hess' law states that ΔH for an overall reaction is the sum of the ΔH values for the individual equations.
B) the molar enthalpy of formation of a compound is equal to the enthalpy change when one mole of the compound is formed from elements.
C) a reaction with a negative enthalpy is exothermic.
D) the enthalpy of formation of an element in its most stable state is equal to zero.
E) the sum of the enthalpies of formation of the products in a chemical reaction is defined as the enthalpy of reaction.

Question 41

All of the following statements are correct EXCEPT

A) in any chemical reaction the change in energies of the system and the surroundings are equal in magnitude but opposite in sign.
B) an expanding gas does work on the surroundings,thus w has a negative value.
C) ΔE = q + w (where q equals heat and w equals work).
D) if a reaction occurs at constant volume,q = ΔE.
E) if a reaction occurs at constant pressure,w = ΔE.

Question 42

Calculate ΔE of a gas for a process in which the gas evolves 24 J of heat and has 9 J of work done on it.

A) −33 J
B) −15 J
C) +15 J
D) +33 J
E) −220 J

Question 43

Calculate ΔE of a gas for a process in which the gas absorbs 25 J of heat and does 7 J of work by expanding.

A) −32 J
B) −18 J
C) +18 J
D) +32 J
E) +180 J

Question 44

Calculate ΔE of a gas for a process in which the gas evolves 8 J of heat and does 16 J of work by expanding.

A) +24 J
B) −2 J
C) +8 J
D) −24 J
E) −8 J

Question 45

You decide to go on a diet to lose 5 lbs (1 lb = 454 g).Fatty tissue consists of about 85% fat and 15% water.In order to lose that much weight how many Calories (kcal)must be eliminated from your normal intake? Fat contains 9.0 kcal/g.

A) 17365 kcal
B) 20600 kcal
C) 3100 kcal
D) 3500 kcal
E) 400 kcal

Question 46

How many kJ are equal to 3.27 L⋅atm of work?

A) 0.331 kJ
B) 3.23 kJ
C) 331 kJ
D) 0.0323 kJ
E) 33.0 kJ

Question 47

The first law of thermodynamics states that

A) the amount of work done on a system is independent of the pathway.
B) the heat flow in or out of a system is independent of the pathway.
C) the total energy change of a system is equal to the sum of the heat absorbed and the work done on the system.
D) both answers a and c
E) both answers b and c

Question 48

In which of the reactions below is ΔH an enthalpy of formation?

A) S₈(s)+ 8O₂(g)→ 8SO₂(g)
B) N₂(g)+ O₂(g)→ 2NO(g)
C) H₂(g)+ Cl₂(g)+ 4O₂(g)→ 2HClO₄(l)
D) Cu(s)+ 1/2I₂(s)→ CuI(s)
E) CH₄(g)+ 2O₂(g)→ CO₂(g)+ 2H₂O(g)