 Chemistry 2e

# Chapter 5

Chemistry 2eChapter 5
1 .

The temperature of 1 gram of burning wood is approximately the same for both a match and a bonfire. This is an intensive property and depends on the material (wood). However, the overall amount of produced heat depends on the amount of material; this is an extensive property. The amount of wood in a bonfire is much greater than that in a match; the total amount of produced heat is also much greater, which is why we can sit around a bonfire to stay warm, but a match would not provide enough heat to keep us from getting cold.

3 .

Heat capacity refers to the heat required to raise the temperature of the mass of the substance 1 degree; specific heat refers to the heat required to raise the temperature of 1 gram of the substance 1 degree. Thus, heat capacity is an extensive property, and specific heat is an intensive one.

5 .

(a) 47.6 J/°C; 11.38 cal °C−1; (b) 407 J/°C; 97.3 cal °C−1

7 .

1310 J; 313 cal

9 .

7.15 °C

11 .

(a) 0.390 J/g °C; (b) Copper is a likely candidate.

13 .

We assume that the density of water is 1.0 g/cm3(1 g/mL) and that it takes as much energy to keep the water at 85 °F as to heat it from 72 °F to 85 °F. We also assume that only the water is going to be heated. Energy required = 7.47 kWh

15 .

lesser; more heat would be lost to the coffee cup and the environment and so ΔT for the water would be lesser and the calculated q would be lesser

17 .

greater, since taking the calorimeter’s heat capacity into account will compensate for the thermal energy transferred to the solution from the calorimeter; this approach includes the calorimeter itself, along with the solution, as “surroundings”: qrxn = −(qsolution + qcalorimeter); since both qsolution and qcalorimeter are negative, including the latter term (qrxn) will yield a greater value for the heat of the dissolution

19 .

The temperature of the coffee will drop 1 degree.

21 .

5.7 $××$ 102 kJ

23 .

38.5 °C

25 .

−2.2 kJ; The heat produced shows that the reaction is exothermic.

27 .

1.4 kJ

29 .

22.6. Since the mass and the heat capacity of the solution is approximately equal to that of the water, the two-fold increase in the amount of water leads to a two-fold decrease of the temperature change.

31 .

11.7 kJ

33 .

30%

35 .

0.24 g

37 .

1.4 $××$ 102 Calories

39 .

The enthalpy change of the indicated reaction is for exactly 1 mol HCL and 1 mol NaOH; the heat in the example is produced by 0.0500 mol HCl and 0.0500 mol NaOH.

41 .

25 kJ mol−1

43 .

81 kJ mol−1

45 .

5204.4 kJ

47 .

1.83 $××$ 10−2 mol

49 .

–802 kJ mol−1

51 .

15.5 kJ/ºC

53 .

7.43 g

55 .

Yes.

57 .

459.6 kJ

59 .

−494 kJ/mol

61 .

44.01 kJ/mol

63 .

−394 kJ

65 .

265 kJ

67 .

90.3 kJ/mol

69 .

(a) −1615.0 kJ mol−1; (b) −484.3 kJ mol−1; (c) 164.2 kJ; (d) −232.1 kJ

71 .

−54.04 kJ mol−1

73 .

−2660 kJ mol−1

75 .

67.1 kJ

77 .

−122.8 kJ

79 .

3.7 kg

81 .

On the assumption that the best rocket fuel is the one that gives off the most heat, B2H6 is the prime candidate.

83 .

−88.2 kJ

85 .

(a) $C3H8(g)+5O2(g)⟶3CO2(g)+4H2O(l);C3H8(g)+5O2(g)⟶3CO2(g)+4H2O(l);$ (b) 1570 L air; (c) −104.5 kJ mol−1; (d) 75.4 °C

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