question archive Chapter 6 Thermochemistry Study Guide 1
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Chapter 6 Thermochemistry Study Guide
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 |
ANS: D
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 |
ANS: A
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. |
ANS: C
4. 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. |
ANS: C
5. 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. |
ANS: B
6. 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 |
ANS: B
7. 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 |
ANS: C
8. 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 |
ANS: B
9. A gas absorbs 825 J of heat and then has 841 J of work done upon it. The change in internal energy of the gas is
A) |
1666 J |
B) |
16 J |
C) |
–16 J |
D) |
–1666 J |
E) |
none of these |
ANS: A
10. Of energy, work, enthalpy, and heat, how many are state functions?
A) |
0 |
B) |
1 |
C) |
2 |
D) |
3 |
E) |
4 |
ANS: C
11. 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 |
ANS: C
12. 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 |
ANS: B
13. 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 |
ANS: E
14. 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 |
ANS: E
15. 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 |
ANS: A
16. 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 |
ANS: B
17. 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 |
ANS: C
18. 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 |
ANS: B
19. 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. |
ANS: E
20. 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 |
ANS: D
21. 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 |
ANS: A
22. 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 |
ANS: E
23. 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 |
ANS: D
24. 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 |
ANS: B
25. 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. |
ANS: D
26. 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 |
ANS: C
27. 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 |
ANS: D
28. 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 |
ANS: A
29. 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)?
2K(s) + ICl(l) ? KCl(s) + KI(s) |
?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 |
ANS: D
30. Which of the following statements is/are true?
I. q (heat) is a state function because ?H is a state function and q = ?H. |
II. When 50.0 g of aluminum at 20.0°C is placed in 50.0 mL of water at 30.0°C, the H2O will undergo a smaller temperature change than the aluminum. (The density of H2O = 1.0 g/mL, specific heat capacity of H2O = 4.18 J/g°C, specific heat capacity of aluminum = 0.89 J/g°C) |
III. When a gas is compressed, the work is negative since the surroundings are doing work on the system and energy flows out of the system. |
IV. For the reaction (at constant pressure) 2N2(g) + 5O2(g) ? 2N2O5(g), the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. |
A) |
I, II, IV |
B) |
II, III |
C) |
II, III, IV |
D) |
II, IV |
E) |
All of the above statements are true. |
ANS: D
31. Consider the following processes:
2A ? (1/2)B + C |
?H1 = 5 kJ/mol |
(3/2)B + 4C ? 2A + C + 3D |
?H2 = –15 kJ/mol |
E + 4A ? C |
?H3 = 10 kJ/mol |
Calculate ?H for: C ? E + 3D
A) |
0 kJ/mol |
B) |
10 kJ/mol |
C) |
–10 kJ/mol |
D) |
–20 kJ/mol |
E) |
20 kJ/mol |
ANS: C
32. At 25°C, the following heats of reaction are known:
|
?H (kJ/mol) |
2ClF + O2 ? Cl2O + F2O |
167.4 |
2ClF3 + 2O2 ? Cl2O + 3F2O |
341.4 |
2F2 + O2 ? 2F2O |
–43.4 |
At the same temperature, calculate ?H for the reaction: ClF + F2 ? ClF3
A) |
–217.5 kJ/mol |
B) |
–130.2 kJ/mol |
C) |
+217.5 kJ/mol |
D) |
–108.7 kJ/mol |
E) |
none of these |
ANS: D
33. Given the heats of the following reactions:
|
|
?H°(kJ) |
I. |
P4(s) + 6Cl2(g) ? 4PCl3(g) |
–1225.6 |
II. |
P4(s) + 5O2(g) ? P4O10(s) |
–2967.3 |
III. |
PCl3(g) + Cl2(g) ? PCl5(g) |
–84.2 |
IV. |
PCl3(g) + |
–285.7 |
Calculate the value of ?H° for the reaction below:
P4O10(s) + 6PCl5(g) ? 10Cl3PO(g)
A) |
–110.5 kJ |
B) |
–610.1 kJ |
C) |
–2682.2 kJ |
D) |
–7555.0 kJ |
E) |
None of these is within 5% of the correct answer. |
ANS: B
34. One of the main advantages of hydrogen as a fuel is that:
A) |
The only product of hydrogen combustion is water. |
B) |
It exists as a free gas. |
C) |
It can be economically supplied by the world's oceans. |
D) |
Plants can economically produce the hydrogen needed. |
E) |
It contains a large amount of energy per unit volume of hydrogen gas. |
ANS: A
35. 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)
ANS:
–290 kJ
36. For the complete combustion of 1.000 mole of ethane gas at 298 K and 1 atm pressure, ?H° = -1560 kJ/mol. What will be the heat released when 4.42 g of ethane is combusted under these conditions?
A) |
–230 kJ |
B) |
230 kJ |
C) |
10588 kJ |
D) |
–10588 kJ |
E) |
none of these |
ANS: B
37. For the complete combustion of 1.000 mole of propane gas at 298 K and 1 atm pressure, ?H° = -2220 kJ/mol. What will be the heat released when 4.13 g of propane is combusted under these conditions?
A) |
–208 kJ |
B) |
208 kJ |
C) |
23651 kJ |
D) |
–23651 kJ |
E) |
none of these |
ANS: B
38. A 36.2 g piece of metal is heated to 81°C and dropped into a calorimeter containing 50.0 g of water (specific heat capacity of water is 4.18 J/g°C) initially at 21.7°C. The empty calorimeter has a heat capacity of 125 J/K. The final temperature of the water is 29.7°C. Ignoring significant figures, calculate the specific heat of the metal..
A) |
1.439 J/gK |
B) |
0.900 J/gK |
C) |
0.360 J/gK |
D) |
0.968 J/gK |
E) |
none of these |
ANS: A
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