Ch 9 Practice Problems
1.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.
2.One mole of an ideal gas is expanded from a volume of 1.50 L to a volume of 10.18 L against a constant external pressure of 1.03 atm. Calculate the work. (1 L• atm = 101.3 J)
A)–8.79 102 J
B)–8.94 J
C)–9.06 102 J
D)–0.0883 J
E)9.06 J
3.A gas absorbs 4.8 J of heat and then performs 13.0 J of work. What is the change in internal energy of the gas?
A)–8.2 J
B)17.8 J
C)–17.8 J
D)8.2 J
E)4.8 J
4.Calculate E for a system that releases 24 J of heat while 57 J of work is done on it.
A)33 J
B)81 J
C)–81 J
D)–33 J
E)24 J
5.For a particular process q = -10 kJ and w = 25 kJ. Which of the following statements is true?
A)Heat flows from the surroundings to the system.
B)The system does work on the surroundings.
C)E = -35 kJ
D)All of these are true.
E)None of these is true.
6.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 is 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 the statements are true.
E)All the statements are false.
7.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)HE
B)The work done in compressing the system must exactly equal the work done by the system in the expansion step.
C)H = 70. J
D)The change in the internal energy for this process is zero.
8.Consider the following reaction:
2SO2(g) + O2(g) 2SO3(g) H = –198 kJ
Calculate the energy change associated with 23.8 g of SO2 reacting with excess O2.
A)-73.5 kJ
B)-36.8 kJ
C)-147 kJ
D)-4.71 103 kJ
E)-198 kJ
9. Consider the following reaction:
2NO(g) + O2(g) 2NO2(g) H = –112 kJ
Is the reaction endothermic or exothermic as written?
A)It is exothermic.
B)It is endothermic.
C)This can't be determined without more information.
10.Which of the following are state functions?
A)work, heat
B)work, heat, enthalpy, energy
C)enthalpy, energy
D)work, heat, enthalpy
E)heat, enthalpy, energy
11.Which of the following statements is(are) true?
A)Enthalpy is a state function.
B)In exothermic reactions, the reactants are lower in potential energy than the products.
C)A chemist takes the point of view of the surroundings when determining the sign for work or heat.
D)The heat of reaction and change in enthalpy can always be used interchangeably.
E)At least two of these statements are true.
12.The H value for the reaction (1/2)O2(g) + Cu(s) CuO(s) is –156 kJ. How much heat is released when 31.9 g of Cu is reacted with oxygen?
A)4.98 103 kJ
B)156 kJ
C)78.4 kJ
D)62.6 kJ
E)311 kJ
13.CH4 + 4Cl2(g) CCl4(g) + 4HCl(g), H = –434 kJ
Based on the above reaction, what energy change occurs when 1.5 mol of methane reacts?
A)6.5 105 J is released.
B)6.5 105 J is absorbed.
C)2.9 105 J is released.
D)2.9 105 J is absorbed.
E)4.3 102 J is released.
14.For the reaction H2O(l) H2O(g) at 298 K, 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
15.Consider the reaction
C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l), H = –1.37 103 kJ
When a 15.6-g sample of ethyl alcohol (molar mass = 46.1 g/mol) is burned, how much energy is released as heat?
A)87.8 kJ
B)2.14 104 kJ
C)4.64 102 kJ
D)4.05 103 kJ
E)4.75 kJ
16.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 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, II, III
C)I, III, IV
D)III, IV
E)I only
17.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), H = –286 kJ
A)3.5 1011 kJ
B)8.18 106 kJ
C)2.86 104 kJ
D)2.34 109 kJ
E)5.72 1010 kJ
18.Given the equation S(s) + O2(g) SO2(g), H = –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)All are true.
B)None is true.
C)I and II are true.
D)I and III are true.
E)Only II is true.
19.Calculate the work for the expansion of an ideal gas from 3.5 to 5.4 L against a pressure of 2.2 atm at constant temperature.
A)4.2 L•atm
B)–4.2 L•atm
C)0
D)4.0 L•atm
E)–0.9 L•atm
Use the following to answer questions 20-23:
Consider a gas in a 1.0-L bulb at STP that is connected via a valve to another bulb that is initally evacuated. Answer the following questions about what occurs when the valve between the two bulbs is opened.
20.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.
21.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.
22.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.
23.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.
Use the following to answer questions 24-27:
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.24. Calculate wAB.
A)-90 L•atm
B)90 L•atm
C)-30 L•atm
D)30 L•atm
E)0
25.Calculate wAC.
A)-90 L•atm
B)90 L•atm
C)-30 L•atm
D)30 L•atm
E)0
26.Calculate qAB.
A)225 L•atm
B)-225 L•atm
C)135 L•atm
D)-135 L•atm
E)none of these
27.Calculate qAC.
A)60 L•atm
B)-60 L•atm
C)100 L•atm
D)-100 L•atm
E)none of these
28.Which statement is true of a process in which 1 mol 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.
29.For the vaporization of water at 1.00 atm,
H = 43.54 kJ/mol at 298 K and H = 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)37.2 J/mol•K
C)2790 J/mol•K
D)75.3 J/mol•K
E)none of these
Use the following to answer questions 30-32:
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.
30.Calculate the difference in E 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
31.Calculate the difference in w between the first sample and the second sample.
A)-2.00 L•atm
B)-1.00 L•atm
C)1.00 L•atm
D)2.00 L•atm
32.Calculate the difference in q between the first sample and the second sample.
A)-2.00 L•atm
B)-1.00 L•atm
C)1.00 L•atm
D)2.00 L•atm
E)none of these
Use the following to answer questions 33-34:
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.
33.Calculate HABD.
A)-25 L•atm
B)25 L•atm
C)-475 L•atm
D)475 L•atm
E)none of these
34.Calculate HACD.
A)-25 L•atm
B)25 L•atm
C)-175 L•atm
D)175 L•atm
E)none of these
35.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.
36.A 22.4-g piece of aluminum (which has a molar heat capacity of 24.03 J/mol°C) is heated to 84.8°C and dropped into a calorimeter containing water (the specific heat capacity of water is 4.18 J/g°C) initially at 22.8°C. The final temperature of the water is 27.0°C. Calculate the mass of water in the calorimeter.
A)6.6 101 g
B)1.8 103 g
C)7.0 101 g
D)2.0 g
E)0.35 g
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)The metal with the higher heat capacity.
B)The metal with the lower heat capacity.
C)Both undergo the same change in temperature.
D)To determine this, you need to know the initial temperatures of the metals.
E)To determine this, you need to know which metals you are talking about.
38.A calorimeter contains 123 g of water at 27.0°C. A block of metal with a mass of 28 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 28.8°C. Calculate the heat capacity per gram of metal. Assume no heat is lost to the calorimeter or the surroundings.
A)2.0 J/g°C
B)0.12 J/g°C
C)6.8 102 J/g°C
D)0.49 J/g°C
E)0.026 J/g°C
39.When 0.157 mol of NH3 is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is H for this reaction per mole of NH3 consumed?
A)–22.7 J
B)–1.08 kJ
C)–44.0 kJ
D)+22.7 J
E)+44.0 kJ
40.You take 326 g of a solid (melting point = 57.6°C, heat of fusion = 346 J/g) and let it melt in 757 g of water. The water temperature decreases from its initial temperature to 57.6°C. Calculate the initial temperature of the water.
A)93.2°C
B)100.0°C
C)22.0°C
D)206.6°C
E)249.8°C
41.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)0.38 J/g°C
B)0.76 J/g°C
C)0.96 J/g°C
D)0.031 J/g°C
E)none of these
42.A calorimeter contains 240 g of water at 21.6°C. A block of metal with a mass of 89 g is heated to 97.9°C and then placed in the water in the calorimeter. After sufficient time, the temperature of the water is measured and found to be 27.0°C. Calculate the specific heat capacity per gram of metal. Assume no heat is lost to the calorimeter or the surroundings.
A)0.12 J/g°C
B)0.86 J/g°C
C)1.2 J/g°C
D)0.21 J/g°C
E)0.028 J/g°C
Use the following to answer questions 43-44:
One mole of a liquid is vaporized at its boiling point, 65°C and 1.00 atm. Hvap for the liquid is 43.8 kJ/mol at 65° C.
43.Calculate w.
A)27.7 J
B)–27.7 J
C)–2.81 103 J
D)2.81 103 J
E)none of these
44.Calculate E.
A)16.1 kJ
B)41.0 kJ
C)46.6 kJ
D)71.5 kJ
E)none of these
45.When a student performs an endothermic reaction in a calorimeter, how (if any) 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 is more negative because the calorimeter always absorbs heat from the reaction.
B)Hcalc is less negative because the calorimeter absorbs heat from the reaction.
C)Hcalc is more positive because the reaction absorbs heat from the calorimeter.
D)Hcalc is less positive because the reaction absorbs heat from the calorimeter.
E)Hcalc equals the actual value because the calorimeter does not absorb heat.
46.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) + 1/2 O2(g) H2O(l)
A)–283.1 kJ/mol
B)–281.9 kJ/mol
C)–285.6 kJ/mol
D)–289.3 kJ/mol
E)283.1 kJ/mol
47.A bomb calorimeter has a heat capacity of 2.18 kJ/K. When a 0.176-g sample of gas with a molar mass of 28.0 g/mol was burned in this calorimeter, the temperature increased by 2.12 K. Calculate the energy of combustion for 1 mol of this gas.
A)–1.29 102 kJ
B)–4.62 kJ
C)–2.63 101 kJ
D)–0.0291 kJ
E)–7.35 102 kJ
48.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)21.2°C
B)20.7°C
C)19.6°C
D)17.5°C
E)none
49.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)7
C)14
D)15
E)126
50.75.0 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)295 K
B)305 K
C)314 K
D)325 K
E)none of these
51.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)0.71 kJ/mol
B)0.83 kJ/mol
C)3.2 kJ/mol
D)3.5 kJ/mol
E)0.059 kJ/mol
52.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)–665 kJ
B)+20.7 kJ
C)–152 kJ
D)+47.4 kJ
E)–569 kJ
53.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)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
54.Calculate H° for the reaction C4H4(g) + 2H2(g) C4H8(g), using the following data:
H°combustion for C4H4(g) = –2341 kJ/mol
H°combustion for H2(g) = –286 kJ/mol
H°combustion for C4H8(g) = –2755 kJ/mol
A)–128 kJ
B)–158 kJ
C)128 kJ
D)158 kJ
E)none of these
55.At 25°C, the following heats of reaction are known:
2C2H2 + 5O2 4CO2 + 2H2O / H = –2600.0 kJC + O2 CO2 / H = –394 kJ
2H2 + O2 2H2O / H = –572 kJ
At the same temperature, calculate H for the following reaction:
2C + H2 C2H2 / H = ?A)226 kJ
B)-226 kJ
C)2422 kJ
D)-2422kJ
E)none of these
56.Using Hess's law and equations 1-3 below, find H° 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) / H° = -1411 kJ2. / C(graphite) + 3H2(g) + (1/2)O2(g) C2H5OH(l) / H° = -278 kJ
3. / C2H4(g) + H2O(l) C2H5OH(l) / H° = -44 kJ
A)44 kJ
B)632 kJ
C)-1367 kJ
D)-1742 kJ
E)none of these
57.Consider the following numbered processes:
1. A 2B
2. B C + D
3. E 2D
H for the process A 2C + E is
A)H1 + H2 + H3
B)H1 + H2
C)H1 + H2 – H3
D)H1 + 2H2 – H3
E)H1 + 2H2 + H3
58.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 following reaction:
ClF + F2 ClF3A)–217.5 kJ/mol
B)–130.2 kJ/mol
C)+217.5 kJ/mol
D)–108.7 kJ/mol
E)none of these
59.Use the following table:
Reaction / H° (kJ)I. P4(s) + 6Cl2(g) 4PCl3(g) / -1225.6
II. P4(s) + 5O2(g) P4O10(g) / -2967.3
III. PCl3(g) + Cl2(g) PCl5(g) / -84.2
IV. PCl3(g) + (1/2)O2(g) Cl3PO(g) / -285.7
Calculate H° for the reaction
P4O10(g) + 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.
60.Given:
Cu2O(s) + (1/2)O2(g) 2CuO(s) / H° = –144 kJCu2O(s) Cu(s) + CuO(s) / H° = +11 kJ
Calculate the standard enthalpy of formation of CuO(s).
A)–166 kJ
B)–299 kJ
C)+299 kJ
D)+155 kJ
E)–155 kJ
61.Given the following two reactions at 298 K and 1 atm, which of the statements is true?
1. N2(g) + O2(g) 2NO(g) H12. NO(g) + (1/2)O2(g) NO2(g) H2
A)Hffor NO2(g) = H2
B)Hffor NO(g) = H1
C)H1= H2
D)Hffor NO2(g) = H2 + (1/2)H1
E)none of these
62.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 16.4-g sample of iron is reacted.
A)–243 kJ
B)–121 kJ
C)–486 kJ
D)–84.9 kJ
E)–826 kJ
63.For which of the following reaction(s) is the enthalpy change for the reaction not equal to H°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 only
B)II only
C)III only
D)I and III
E)II and III
Ans:D Chapter/Section:9.6 Difficulty:easy Keyword1:generalchemistry
64.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)–542 kJ/mol
B)542 kJ/mol
C)–271 kJ/mol
D)–1084 kJ/mol
E)none of these
65.Choose the correct equation for the standard enthalpy of formation of CO(g), where H°ffor CO = –110.5 kJ/mol.
A)2Cgraphite(s) + O2(g) 2CO(g), H° = –110.5 kJ
B)Cgraphite(s) + O(g) CO(g), H° = –110.5 kJ
C)Cgraphite(s) + 1/2O2(g) CO(g), H° = –110.5 kJ
D)Cgraphite(s) + CO2(g) 2CO(g), H° = –110.5 kJ
E)CO(g) Cgraphite(s) + O(g), H° = –110.5 kJ
66.The combustion of methanol takes place according to the reaction
2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(l)
Calculate H for the combustion of 1 mol of methanol under standard conditions. Use the following standard enthalpies of formation:
H°f for CH3OH(l) = -238.5 kJ/molH°ffor CO2(g) = -393.5 kJ/mol
H°f for H2O(l) = -285.6 kJ/mol
A)+726.2 kJ/mol
B)-726.2 kJ/mol
C)+1452.4 kJ/mol
D)-1452.4 kJ/mol
E)none of these
67.The enthalpy of formation of an element in its standard state is
A)the enthalpy of its reaction with hydrogen.
B)the enthalpy of its reaction with oxygen.
C)determined by its melting point.
D)zero.
E)none of these
68.The heat combustion of acetylene, C2H2(g), at 25°C, is –1299 kJ/mol. At this temperature, H°fvalues for CO2(g) and H2O(l) are –393 and –286 kJ/mol, respectively. Calculate H°ffor acetylene.
A)2376 kJ/mol
B)625 kJ/mol
C)227 kJ/mol
D)–625 kJ/mol
E)none of these
69.For the reaction
AgI(s) + (1/2)Br2(g) AgBr(s) + (1/2)I2(s), H° = –54.0 kJ
H°f for AgBr(s) = –100.4 kJ/mol
H°ffor Br2(g) = +30.9 kJ/mol
The value of H°ffor AgI(s) is
A)–123.5 kJ/mol
B)+77.3 kJ/mol
C)+61.8 kJ/mol
D)–77.3 kJ/mol
E)–61.8 kJ/mol
70.Using the following data, calculate the standard heat of formation of ICl(g) in kJ/mol.
H° (kJ/mol)Cl2(g) 2Cl(g) / 242.3
I2 (g) 2I(g) / 151.0
ICl(g) I(g) + Cl(g) / 211.3
I2(s) I2(g) / 62.8
A)–211 kJ/mol
B)–14.6 kJ/mol
C)16.8 kJ/mol
D)245 kJ/mol
E)439 kJ/mol
71.Using the information below, calculate H°ffor PbO(s).
PbO(s) + CO(g) Pb(s) + CO2(g), H° = –131.4 kJ
H°f for CO2(g) = –393.5 kJ/mol
H°ffor CO(g) = –110.5 kJ/mol
A)–151.6 kJ/mol
B)–283.0 kJ/mol
C)+283.0 kJ/mol
D)–372.6 kJ/mol
E)+252.1 kJ/mol
72.Using the information below, calculate H°ffor CH3OH(l).
2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(l), H° = –1453 kJ
H°ffor CO2(g) = –393.5 kJ/mol
H°ffor H2O(l) = –286 kJ/mol
A)–239 kJ/mol
B)774 kJ/mol
C)–3.38 103 kJ/mol
D)–774 kJ/mol
E)239 kJ/mol
73.Consider the following reaction:
2Al(s) + 3Cl2(g) 2AlCl3(s), H = –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?
74.Consider the following data:
H (kJ)Ca(s) + 2C(graphite) CaC2(s) / –62.8
Ca(s) + 1/2O2(g) CaO(s) / –635.5
CaO(s) + H2O(l) Ca(OH)2(aq) / –653.1
C2H2(g) + (5/2)O2(g) 2CO2 + H2O(l) / –1300.
C(graphite) + O2(g) CO2(g) / –393.51
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)
75.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)
76.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.
Answers
1. / C / 11. / A / 21. / B / 31. / C / 41. / A / 51. / D / 61. / D / 71. / A2. / C / 12. / C / 22. / B / 32. / B / 42. / B / 52. / A / 62. / B / 72. / A
3. / A / 13. / A / 23. / B / 33. / A / 43. / C / 53. / A / 63. / D
4. / A / 14. / B / 24. / A / 34. / A / 44. / B / 54. / B / 64. / C
5. / E / 15. / C / 25. / E / 35. / E / 45. / D / 55. / A / 65. / C
6. / C / 16. / A / 26. / A / 36. / A / 46. / B / 56. / C / 66. / B
7. / D / 17. / D / 27. / B / 37. / A / 47. / E / 57. / D / 67. / D
8. / B / 18. / A / 28. / E / 38. / D / 48. / C / 58. / D / 68. / C
9. / A / 19. / B / 29. / B / 39. / C / 49. / B / 59. / B / 69. / E
10. / C / 20. / B / 30. / A / 40. / A / 50. / C / 60. / E / 70. / C
73. a. exothermic b. 52.2 kJ c. 0.0388 g Al
74. -713 kJ
75. -290 kJ
76. The energy available from the combustion of a volume of acetylene is 0.452 times as large as the energy available from an equal volume of butane