10 Answer Key Chapter 5
Solution Videos
| 5.1 Energy Basics | ||
| 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 | |
| 5.2 Calorimetry | ||
| 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 | |
| 5.2 Enthalpy | ||
| 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. | –66.4 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) + 5 O2 (g) → 3 CO2 (g) + 4 H2O (l) |
| (b) | 330 L air | |
| (c) | −104.5 kJ mol−1 | |
| (d) | 75.4 °C | |
