Chapter 6: Thermochemistry
1. A gas absorbs 0.0 J of heat and then performs 30.7 J of work. The change in internal energy
of the gas is
A)
61.4 J
B)
30.7 J
C)
–61.4 J
D)
–30.7 J
E)
none of these
2. What is the kinetic energy of a 1.56-kg object moving at 94.0 km/hr?
A)
5.32 102 kJ
B)
6.89 103 kJ
C)
5.32 10–4 kJ
D)
1.06 103 kJ
E)
2.04 101 kJ
3. Which of the following statements correctly describes the signs of q and w for the following
exothermic process at P = 1 atm and T = 370 K?
H2O(g) → H2O(l)
A)
q and w are negative.
B)
q is positive, w is negative.
C)
q is negative, w is positive.
D)
q and w are both positive.
E)
q and w are both zero.
4. For a particular process q = 20 kJ and w = 15 kJ. Which of the following statements is true?
A)
Heat flows from the system to the surroundings.
B)
The system does work on the surroundings.
C)
E = 35 kJ
D)
All of the above are true.
E)
None of the above are true.
5. Which of the following statements is correct?
A)
The internal energy of a system increases when more work is done by the system
than heat was flowing into the system.
B)
The internal energy of a system decreases when work is done on the system and
heat is flowing into the system.
C)
The system does work on the surroundings when an ideal gas expands against a
constant external pressure.
D)
All statements are true.
E)
All statements are false.
6. For a particular process q = –17 kJ and w = 21 kJ. Which of the following statements is
false?
A)
Heat flows from the system to the surroundings.
B)
The system does work on the surroundings.
C)
E = +4 kJ
D)
The process is exothermic.
E)
None of the above is false.
7. One mole of an ideal gas is expanded from a volume of 1.00 liter to a volume of 8.93 liters
against a constant external pressure of 1.00 atm. How much work (in joules) is performed
on the surroundings? Ignore significant figures for this problem. (T = 300 K; 1 L·atm =
101.3 J)
A)
402 J
B)
803 J
C)
2.41 103 J
D)
905 J
E)
none of these
8. Calculate the work for the expansion of CO2 from 1.0 to 4.7 liters against a pressure of 1.0
atm at constant temperature.
A)
3.7 L·atm
B)
4.7 L·atm
C)
0 L·atm
D)
–3.7 L·atm
E)
–4.7 L·atm
9. A fuel-air mixture is placed in a cylinder fitted with a piston. The original volume is 0.310-
L. When the mixture is ignited, gases are produced and 935 J of energy is released. To what
volume will the gases expand against a constant pressure of 635 mmHg, if all the energy
released is converted to work to push the piston?
A)
10.7 L
B)
8.02 L
C)
11.4 L
D)
11.0 L
E)
1.78 L
10. Which statement is true of a process in which one mole of a gas is expanded from state A to
state B?
A)
When the gas expands from state A to state B, the surroundings are doing work on
the system.
B)
The amount of work done in the process must be the same, regardless of the path.
C)
It is not possible to have more than one path for a change of state.
D)
The final volume of the gas will depend on the path taken.
E)
The amount of heat released in the process will depend on the path taken.
11. Calculate the work associated with the expansion of a gas from 42.0 L to 79.0 L at a
constant pressure of 14.0 atm.
A)
518 L·atm
B)
–518 L·atm
C)
–1.11 103 L·atm
D)
588 L·atm
E)
1.11 103 L·atm
12. Calculate the work associated with the compression of a gas from 121.0 L to 80.0 L at a
constant pressure of 13.1 atm.
A)
–537 L atm
B)
537 L atm
C)
3.13 L atm
D)
–3.13 L atm
E)
101 L atm
13. According to the first law of thermodynamics, the energy of the universe is constant. Does
this mean that E is always equal to zero?
A)
Yes, E = 0 at all times, which is why q = –w.
B)
No, E does not always equal zero, but this is only due to factors like friction and
heat.
C)
No, E does not always equal zero because it refers to the system’s internal energy,
which is affected by heat and work.
D)
No, E never equals zero because work is always being done on the system or by
the system.
E)
No, E never equals zero because energy is always flowing between the system
and surroundings.
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 concerning what occurs when the valve between
the two bulbs is opened.
14. What is true about the value of q?
A)
It is greater than zero.
B)
It is equal to zero.
C)
It is less than zero.
D)
More information is needed.
E)
None of these.
15. What is true about the value of w?
A)
It is greater than zero.
B)
It is equal to zero.
C)
It is less than zero.
D)
More information is needed.
E)
None of these.
16. What is true about the value of E?
A)
It is greater than zero.
B)
It is equal to zero.
C)
It is less than zero.
D)
More information is needed.
E)
None of these.
17. What is true about the value of H?
A)
It is greater than zero.
B)
It is equal to zero.
C)
It is less than zero.
D)
More information is needed.
E)
None of these.
18. A property that is independent of the pathway is called an intensive property.
19. A state function does not depend on the system’s past or future.
20. When a system performs work on the surroundings, the work is reported with a negative
sign.
21. In exothermic reaction, potential energy stored in chemical bonds is being converted to
thermal energy via heat.
22. Of energy, work, enthalpy, and heat, how many are state functions?
A)
0
B)
1
C)
2
D)
3
E)
4
23. Which of the following properties is (are) intensive properties?
I. mass
II. temperature
III. volume
IV. concentration
V. energy
A)
I, III, and V
B)
II only
C)
II and IV
D)
III and IV
E)
I and V
24. For the reaction H2O(l) → H2O(g) at 298 K and 1.0 atm, H is more positive than E 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 difference in the H–O bond energy in H2O(l) compared to H2O(g)
D)
the value of H itself
E)
none of these
25. Which one of the following statements is false?
A)
The change in internal energy, E, for a process is equal to the amount of heat
absorbed at constant volume, qv.
B)
The change in enthalpy, H, for a process is equal to the amount of heat absorbed
at constant pressure, qp.
C)
A bomb calorimeter measures H directly.
D)
If qp for a process is negative, the process is exothermic.
E)
The freezing of water is an example of an exothermic reaction.
26. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l), H = –1.37 103 kJ
For the combustion of ethyl alcohol as described in the above equation, which of the
following is true?
I. The reaction is exothermic.
II. The enthalpy change would be different if gaseous water was 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, II, III
C)
I, III, IV
D)
III, IV
E)
only I
27. Consider the reaction:
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l); H = –1.37 103 kJ
Consider the following propositions:
I. The reaction is endothermic
II. The reaction is exothermic.
III. The enthalpy term would be different if the water formed was gaseous.
Which of these propositions is (are) true?
A)
I
B)
II
C)
III
D)
I, II
E)
II, III
28. How much heat is required to raise the temperature of a 5.75-g sample of iron (specific heat
= 0.450 J/g°C) from 25.0°C to 79.8°C?
A)
2.54 J
B)
315 J
C)
700 J
D)
848 J
E)
142 J
29. Two metals of equal mass with different heat capacities are subjected to the same amount of
heat. Which undergoes the smallest change in temperature?
A)
The metal with the higher heat capacity.
B)
The metal with the lower heat capacity.
C)
Both undergo the same change in temperature.
D)
You need to know the initial temperatures of the metals.
E)
You need to know which metals you have.
30. A 32.5 g piece of aluminum (which has a molar heat capacity of 24.03 J/°C·mol) is heated
to 82.4°C and dropped into a calorimeter containing water (specific heat capacity of water is
4.18 J/g°C) initially at 22.3°C. The final temperature of the water is 24.2°C. Ignoring
significant figures, calculate the mass of water in the calorimeter.
A)
212 g
B)
5.72 kg
C)
6.42 g
D)
1.68 kg
E)
none of these
31. A 45.9 g sample of a metal is heated to 95.2°C and then placed in a calorimeter containing
120.0 g of water (c = 4.18 J/g°C) at 21.6°C. The final temperature of the water is 24.5°C.
Which metal was used?
A)
Aluminum (c = 0.89 J/g°C)
B)
Iron (c = 0.45 J/g°C)
C)
Copper (c = 0.20 J/g°C)
D)
Lead (c = 0.14 J/g°C)
E)
none of these
32. You take 295.5 g of a solid at 30.0°C and let it melt in 425 g of water. The water
temperature decreases from 85.1°C to 30.0°C. Calculate the heat of fusion of this solid.
A)
160 J/g
B)
166 J/g
C)
331 J/g
D)
721 J/g
E)
cannot solve without the heat capacity of the solid
33. 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 one mole of
water, necessary to cool 500 g of liquid water initially at 20°C to 0°C?
A)
1
B)
7
C)
14
D)
15
E)
126
34. 30.0 mL of pure water at 282 K is mixed with 50.0 mL of pure water at 306 K. What is the
final temperature of the mixture?
A)
294 K
B)
297 K
C)
342 K
D)
588 K
E)
24 K
35. Consider the reaction
H2(g) + O2(g) → H2O(l) H° = –286 kJ
Which of the following is true?
A)
The reaction is exothermic.
B)
The reaction is endothermic.
C)
The enthalpy of the products is less than that of the reactants.
D)
Heat is absorbed by the system.
E)
Both A and C are true.
36. In the lab, you mix two solutions (each originally at the same temperature) and the
temperature of the resulting solution decreases. Which of the following is true?
A)
The chemical reaction is releasing energy.
B)
The energy released is equal to s m T.
C)
The chemical reaction is absorbing energy.
D)
The chemical reaction is exothermic.
E)
More than one of these.
37. What is the specific heat capacity of a metal if it requires 178.1 J to change the temperature
of 15.0 g of the metal from 25.00°C to 32.00°C?
A)
0.590 J/g°C
B)
11.9 J/g°C
C)
25.4 J/g°C
D)
1.70 J/g°C
E)
283 J/g°C
38. A 140.0-g sample of water at 25.0°C is mixed with 111.7 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 specific heat capacity of the metal, assuming it is constant over the temperature
range concerned?
A)
0.34 J/g°C
B)
0.68 J/g°C
C)
0.22 J/g°C
D)
2.9 J/g°C
E)
none of these
39. If 5.0 kJ of energy is added to a 15.5-g sample of water at 10.°C, the water is
A)
boiling
B)
completely vaporized
C)
frozen solid
D)
decomposed
E)
still a liquid
40. Exactly 123.7 J will raise the temperature of 10.0 g of a metal from 25.0°C to 60.0°C. What
is the specific heat capacity of the metal?
A)
2.83 J/g°C
B)
0.353 J/g°C
C)
24.9 J/g°C
D)
29.6 J/g°C
E)
none of these
41. A chunk of lead at 91.6°C was added to 200.0 g of water at 15.5°C. The specific heat of lead
is 0.129 J/g°C, and the specific heat of water is 4.18 J/g°C. When the temperature stabilized,
the temperature of the mixture was 17.9°C. Assuming no heat was lost to the surroundings,
what was the mass of lead added?
A)
1.57 kg
B)
170 g
C)
204 g
D)
211 g
E)
none of these
42. On a cold winter day, a steel metal fence post feels colder than a wooden fence post of
identical size because:
A)
The specific heat capacity of steel is higher than the specific heat capacity of
wood.
B)
The specific heat capacity of steel is lower than the specific heat capacity of wood.
C)
Steel has the ability to resist a temperature change better than wood.
D)
The mass of steel is less than wood so it loses heat faster.
E)
Two of the above statements are true.
43. What is the specific heat capacity of silver if it requires 86.3 J to raise the temperature of 15
grams of silver by 25°C?
A)
4.3 J/g°C
B)
0.23 J/g°C
C)
0.14 J/g°C
D)
0.60 J/g°C
E)
none of these
44. A 4.4-g sample of Colorado oil shale is burned in a bomb calorimeter, which causes the
temperature of the calorimeter to increase by 5.0°C. The calorimeter contains 1.00 kg of
water (heat capacity of H2O = 4.184 J/g°C) and the heat capacity of the empty calorimeter is
0.10 kJ/°C. How much heat is released per gram of oil shale when it is burned?
A)
21 kJ/g
B)
42 kJ/g
C)
0 kJ/g
D)
4.9 kJ/g
E)
0.21 kJ/g
45. If a student performs an endothermic reaction in a calorimeter, how does the calculated
value of H differ from the actual value if the heat exchanged with the calorimeter is not
taken into account?
A)
Hcalc would be more negative because the calorimeter always absorbs heat from
the reaction.
B)
Hcalc would be less negative because the calorimeter would absorb heat from the
reaction.
C)
Hcalc would be more positive because the reaction absorbs heat from the
calorimeter.
D)
Hcalc would be less positive because the reaction absorbs heat from the
calorimeter.
E)
Hcalc would equal the actual value because the calorimeter does not absorb heat.
46. A bomb calorimeter has a heat capacity of 2.47 kJ/K. When a 0.109-g sample of ethylene
(C2H4) was burned in this calorimeter, the temperature increased by 2.22 K. Calculate the
energy of combustion for one mole of ethylene.
A)
–5.29 kJ/mol
B)
–50.3 kJ/mol
C)
–636 kJ/mol
D)
–0.269 kJ/mol
E)
–1.41 103 kJ/mol
47. Consider the reaction:
When a 21.1-g sample of ethyl alcohol (molar mass = 46.07 g/mol) is burned, how much
energy is released as heat?
A)
0.458 kJ
B)
0.627 kJ
C)
6.27 102 kJ
D)
2.89 104 kJ
E)
2.18 kJ
48. The H value for the reaction is -90.8 kJ. How much heat is
released when 66.9 g Hg is reacted with oxygen?
A)
0.333 kJ
B)
6.07 103 kJ
C)
30.3 kJ
D)
90.8 kJ
E)
none of these
49. The total volume of hydrogen gas needed to fill the Hindenburg was 2.11 108 L at 1.00
atm and 24.7°C. How much energy was evolved when it burned?
A)
8.64 106 kJ
B)
2.98 1010 kJ
C)
3.02 104 kJ
D)
2.47 109 kJ
E)
4.94 109 kJ
50. CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g), H = –434 kJ
Based on the above reaction, what energy change occurs when 1.2 moles of methane (CH4)
reacts?
A)
5.2 105 J are released.
B)
5.2 105 J are absorbed.
C)
3.6 105 J are released.
D)
3.6 105 J are absorbed.
E)
4.4 105 J are released.
51. Given the equation S(s) + O2(g) → SO2(g), H = –296 kJ, which of the following
statement(s) is (are) true?
I. The reaction is exothermic.
II. When 0.500 mole sulfur is reacted, 148 kJ of energy is released.
III. When 32.0 g of sulfur are burned, 2.96 105 J of energy is released.
A)
All are true.
B)
None is true.
C)
I and II are true.
D)
I and III are true.
E)
Only II is true.
52. When 0.236 mol of a weak base (A–) is reacted with excess HCl, 6.91 kJ of energy is
released as heat. What is H for this reaction per mole of A– consumed?
A)
–34.2 kJ
B)
–59.4 kJ
C)
–29.3 kJ
D)
34.2 kJ
E)
29.3 kJ
53. What is the enthalpy change when 49.4 mL of 0.430 M sulfuric acid reacts with 23.3 mL of
0.309 M potassium hydroxide?
H2SO4(aq) + 2KOH(aq) → K2SO4(aq) +
2H2O(l)
H° = –111.6 kJ/mol
A)
–0.402 kJ
B)
–3.17 kJ
C)
–2.37 kJ
D)
–0.803 kJ
E)
–112 kJ
54. How much heat is liberated at constant pressure when 2.35 g of potassium metal reacts with
5.68 mL of liquid iodine monochloride (d = 3.24 g/mL)?
H° = –740.71 kJ/mol
A)
2.22 103 kJ
B)
8.40 101 kJ
C)
1.28 102 kJ
D)
2.23 101 kJ
E)
7.41 102 kJ
55. Consider the following specific heats of metals.
Metal
Specific Heat
Zinc
0.387 J/(g°C)
Magnesium
1.02 J/(g°C)
Iron
0.450 J/(g°C)
Silver
0.237 J/(g°C)
Lead
0.127 J/(g°C)
If the same amount of heat is added to 25.0 g of each of the metals, which are all at the same
initial temperature, which metal will have the highest temperature?
A)
Zinc
B)
Magnesium
C)
Iron
D)
Silver
E)
Lead