Chemistry Chapter 6
28. [Algorithmic] A 140.0-g sample of water at 25.0C is mixed with 100.0 g of a certain metal at 100.0C. After thermal equilibrium is established, the (final) temperature of the mixture is 29.6C. What is the heat capacity of the metal, assuming it is constant over the temperature range concerned? a) 0.38 J/gC b) 0.76 J/gC c) 0.96 J/gC d) 0.031 J/gC e) none of these
ANS: a)
31. 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 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) Only I
ANS: a)
36. CH4 + 4Cl2 (g) CCl4 (g) + 4HCl(g), H = -434 kJ Based on the above reaction, what energy change occurs when 1.2 moles of methane 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
ANS: a)
37. 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.
ANS: a)
59. Using the information below, calculate H f for PbO(s) PbO(s) + CO(g) Pb(s) + CO2 (g) H• = -131.4 kJ H f for CO2 (g) = -393.5 kJ/mol H f for 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
ANS: a)
83. Consider the reaction: 2ClF3(g) + 2NH3(g) N2(g) + 6HF(g) + Cl2(g) When calculating the ΔHoRXN, why is the ΔHf o for N2 not important? a) Because nitrogen is in its standard elemental state and no energy is needed for this product to exist. b) Because any element or compound in the gaseous state requires a negligible amount of energy to exist. c) Because the products are not included when calculating ΔHoRXN. d) Because nitrogen is in its elemental state and does not contribute to the reaction itself. e) Two of the above statements explain why N2 is not important when calculating ΔHoRXN.
ANS: a)
A 25.0 g piece of aluminum (which has a molar heat capacity of 24.03 J/Cmol) is heated to 82.4C and dropped into a calorimeter containing water (specific heat capacity of water is 4.18J/gC) initially at 22.3C. The final temperature of the water is 24.9C. Calculate the mass of water in the calorimeter. a) 118 g b) 6.57 g c) 3180 g d) 2120 g e) none of these
ANS: a)
Consider a rigid insulated box containing 20.0 g of He(g) at 25.0C and 1.00 atm in one compartment and 20.0 g of N2 (g) at 115.0C and 2.00 atm in the other compartment. These compartments are connected by a partition which transmits heat. What will be the final temperature in the box at thermal equilibrium? (Cv (He)= 12.5 J/K mol, Cv (N2 )= 20.7 J/K mol) a) 42.2C b) 58.9C c) 70.0C d) 81.0C e) none of these
ANS: a)
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.
ANS: a)
29. 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
ANS: b)
30.0 mL of pure water at 280. K is mixed with 50.0 mL of pure water at 330. K. What is the final temperature of the mixture? a) 290. K b) 311 K c) 320. K d) 326 K e) 405 K
ANS: b)
34. [Algorithmic] Exactly 313.5 J will raise the temperature of 10.0 g of a metal from 25.0C to 60.0C. What is the specific heat capacity of the metal? a) 3.74 J/gC b) 0.896 J/gC c) 9.70 J/gC d) 1.73 J/gC e) none of these
ANS: b)
39. What is the specific heat capacity of gold if it requires 48.8 J to raise the temperature of 15 grams of gold 25C? a) 29 J/gC b) 0.13 J/gC c) 79 J/gC d) 0.011 J/gC e) none of these
ANS: b)
40. [Algorithmic] 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 55.8-g sample of iron is reacted. a) -206 kJ b) -413 kJ c) -826 kJ d) -1650 kJ e) -3.30 103 kJ
ANS: b)
51. Calculate H for the reaction C4H4 (g) + 2H2 (g) C4H8 (g), using the following data: Hcombustion for C4H4 (g) = -2341 kJ/mol Hcombustion for H2 (g) = -286 kJ/mol Hcombustion for C4H8 (g) = -2755 kJ/mol a) -128 kJ b) -158 kJ c) 128 kJ d) 158 kJ e) none of these
ANS: b)
53. 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) + (1/2)O2 (g) Cl3PO(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)
81. 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.
ANS: b)
A 40.2 g sample of a metal is heated to 99.3C and then placed in a calorimeter containing 120.0 g of water (c=4.18J/gC) at 21.8C. The final temperature of the water is 24.5C. Which metal was used? a) Aluminum (c=0.89J/gC) b) Iron (c=0.45J/gC) c) Copper (c = 0.20J/gC) d) Lead (c=0.14J/gC) e) none of these
ANS: b)
Calculate the work associated with the compression of a gas from 121 L to 80. L at a constant pressure of 11 atm. a) -450 L atm b) 450 L atm c) 3.7 L atm d) -3.7 L atm e) 120 L atm
ANS: b)
Calculate the work associated with the expansion of a gas from 152.0 L to 189.0 L at a constant pressure of 14.0 atm. a) 518 L atm b) -518 L atm c) -259 L atm d) 171 L atm e) 259 L atm
ANS: b)
The enthalpy of fusion of ice is 6.020 kJ/mol. The heat capacity of liquid water is 75.4 J/molC. What is the smallest number of ice cubes at 0C, each containing one mole of water, necessary to cool 500. g of liquid water initially at 20C to 0C? a) 1 b) 7 c) 14 d) 15 e) 126
ANS: b)
One mole of an ideal gas is expanded from a volume of 1.00 liter to a volume of 10.00 liters against a constant external pressure of 1.00 atm. How much work (in joules) is performed on the surroundings? (T = 300 K; 1 L atm = 101.3 J) a) 456 J b) 912 J c) 2740 J d) 2870 J e) none of these
ANS: b) 1.00 atm x (101,300 Pa / atm) = 101,300 Pa = 101,300 N/m^2 9.00 L = 9.00 dm^3 x (1 m / 10 dm)^3 = 0.00900 m^3 work = -(101,300 N/m^2)(0.00900 m^3) = 912 N m = 912 J
26. 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.
ANS: c)
30. [Algorithmic] Consider the reaction C2H5OH(l) + 3O2 (g) 2CO2 (g) + 3H2O(l), H = -1.37 103 kJ When a 15.1-g sample of ethyl alcohol (molar mass = 46.1 g/mol) is burned, how much energy is released as heat? a) 0.449 kJ b) 2.25 103 kJ c) 4.49 102 kJ d) 1.02 103 kJ e) 196 kJ
ANS: c)
32. [Algorithmic] The H value for the reaction (1/2)O2 (g) + Hg(l) HgO(s) is -90.8 kJ. How much heat is released when 32.5 g Hg is reacted with oxygen? a) 9.32 kJ b) 90.8 kJ c) 14.7 kJ d) 40.0 kJ e) none of these
ANS: c)
41. [Algorithmic] When 0.157 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) -22.7 J b) -1.08 kJ c) -44.0 kJ d) +22.7 J e) +44.0 kJ
ANS: c)
46. Consider the following processes: 2A 1/2B + 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)
47. Consider the following processes: H (kJ/mol) (1/2)A B 150. 3B 2C + D -125. E + A D 350. Calculate H for: B + D E + 2C a) 325 kJ/mol b) 525 kJ/mol c) -175 kJ/mol d) -325 kJ/mol e) none of these
ANS: c)
48. Which of the following does not have a standard enthalpy of formation equal to zero at 25C and 1.0 atm? a) F2 (g) b) Al(s) c) H2O(l) d) H2 (g) e) They all have a standard enthalpy equal to zero.
ANS: c)
55. The heat combustion of acetylene, C2H2 (g), at 25C, is -1299 kJ/mol. At this temperature, H f values for CO2 (g) and H2O(l) are -393 and -286 kJ/mol, respectively. Calculate H f for acetylene. a) 2376 kJ/mol b) 625 kJ/mol c) 227 kJ/mol d) -625 kJ/mol e) none of these
ANS: c)
56. Choose the correct equation for the standard enthalpy of formation of CO(g), where H f for CO = -110.5 kJ/mol (gr indicates graphite). a) 2C(gr) + O2 (g) 2CO(g), H = -110.5 kJ b) C(gr) + O(g) CO(g), H = -110.5 kJ c) C(gr) + (1/2)O2(g) CO(g), H = -110.5 kJ d) C(gr) + CO2 (g) 2CO(g), H = -110.5 kJ e) CO(g) C(gr) + O(g), H = -110.5 kJ
ANS: c)
58. Using the following data, calculate the standard heat of formation of the compound ICl 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
ANS: c)
82. According to the first law of thermodynamics, the energy of the universe is constant. Does this mean that ΔE is always equal to zero? a) Yes, ΔE = 0 at all times, which is why q = -w. b) No, ΔE does not always equal zero but this is only due to factors like friction and heat. c) No, ΔE does not always equal zero because it refers to the system's internal energy which is affected by heat and work. d) No, ΔE never equals zero because work is always being done on the system or by the system. e) No, ΔE never equals zero because energy is always flowing between the system and surroundings.
ANS: c)
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: c)
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.
ANS: c)
Of energy, work, enthalpy, and heat, how many are state functions? a) 0 b) 1 c) 2 d) 3 e) 4
ANS: c)
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)
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)
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)
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.
ANS: c)
You take 200. g of a solid at 30.0C and let it melt in 400. g of water. The water temperature decreases from 85.1C to 30.0C. Calculate the heat of fusion of this solid. a) 125 J/g b) 285 J/g c) 461 J/g d) 518 J/g e) cannot solve without the heat capacity of the solid
ANS: c)
27. [Algorithmic] What is the heat capacity of mercury if it requires 167.0 J to change the temperature of 15.0 g mercury from 25.00C to 33.00C? a) 6.92 10-3 J/gC b) 1.12 10-2 J/gC c) 0.445 J/gC d) 1.39 J/gC e) 313 J/gC
ANS: d)
35. [Algorithmic] The total volume of hydrogen gas needed to fill the Hindenburg was 2.00 108 L at 1.00 atm and 25.0C. 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
ANS: d)
42. [Algorithmic] A 4.0-g sample of Colorado oil shale is burned in a bomb calorimeter, which causes the temperature of the calorimeter to increase by 5.0C. The calorimeter contains 1.00 kg of water (CH2O = 4.184 J/gC) 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) 5.4 kJ/g e) 5.2 kJ/g
ANS: d)
43. 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)
49. Consider the following numbered processes: I. A 2B II. B C + D III. 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
ANS: d)
50. At 25C, the following heats of reaction are known: H (kJ/mol) 2ClF + O2 Cl2O + F2O 167.4 2CIF3 + 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)
52. Given the following two reactions at 298 K and 1 atm, which of the statements is true? 1. N2 (g) + O2 (g) 2NO(g) H1 2. NO(g) + (1/2)O2 (g) NO2 (g) H2 a) H f for NO2 (g) = H2 b) H f for NO(g) = H1 c) H f = H2 d) H f for NO2 (g) = H2 + (1/2)H1 e) none of these
ANS: d)
60. 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 b) II c) III d) I and III e) II and III
ANS: d)
84. Which of the following statements is/are true? I. q (heat) is a state function because ΔH is a state function and q = ΔH. II. When 50.0 g of aluminum at 20.0oC is placed in 50.0 mL of water at 30.0oC, 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/oC•g, specific heat capacity of aluminum = 0.89 J/oC•g) III. When a gas is compressed, the work is negative since the surroundings is 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)
A gas absorbs 0.0 J of heat and then performs 15.2 J of work. The change in internal energy of the gas is a) -24.8 J b) 14.8 J c) 55.2 J d) -15.2 J e) none of these
ANS: d)
Calculate the work for the expansion of CO2 from 1.0 to 2.5 liters against a pressure of 1.0 atm at constant temperature. a) 1.5 liter atm b) 2.5 liter atm c) 0 d) -1.5 liter atm e) -2.5 liter atm
ANS: d)
25. Consider the reaction H2(g) + (1/2)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)
33. 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)
38. 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)
44. [Algorithmic] A bomb calorimeter has a heat capacity of 2.47 kJ/K. When a 0.105-g sample of ethylene (C2H4 ) was burned in this calorimeter, the temperature increased by 2.14 K. Calculate the energy of combustion for one mole of ethylene. a) -5.29 kJ b) -50.3 kJ c) -572 kJ d) -661 kJ e) -1.41 103 kJ
ANS: e)
45. [Algorithmic] How much heat is required to raise the temperature of a 6.21-g sample of iron (specific heat = 0.450 J/(gC) from 25.0C to 79.8C? a) 70.0 J b) 101 J c) 386 J d) 756 J e) 153 J
ANS: e)
54. Given: Cu2O(s) + (1/2)O2 (g) 2CuO(s) H = -144 kJ Cu2O(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
ANS: e)
57. For the reaction AgI(s) + (1/2)Br2 (g) AgBr(s) + (1/2)I2 (s), H 298 = -54.0 kJ H f for AgBr(s) = -100.4 kJ/mol H f for Br2 (g) = +30.9 kJ/mol The value of H f (298) for 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
ANS: e)
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.
ANS: e)
10-13. 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. 10. 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 11. 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 12. 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 13. 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
10.ANS: b) 11.ANS: b) 12.ANS: b) 13.ANS: b)
