Chapter 12 Problems
1. When 1 mol of fuel is burned at constant pressure, it produces 3452 kJ of heat and does 11 kJ of work. What is the value of `DeltaU` for the combustion of the fuel?
2. Consider the following thermal chemical equation for the combustion of acetone (C_3H_6O), the main ingredient in nail polish remover:
`C_3H_6O(l) + 4O_2(g) -> 3CO_2(g) +3H_2O(g)` `DeltaH_"rxn"= -1790 kJ`
If a bottle of nail polish remover contains 177mL of acetone, how much heat would be released by its complete combustion? The density of acetone is 0.788 g/mL.
3. A calorimeter contained 75.0 g of water at 16.95°C. A 93.3 g iron sample at 65.58°C was placed in it, giving a final temperature of 19.68°C for the system. Calculate the heat capacity of the calorimeter. Specific heats are 4.184 J/g·°C for water and 0.444 J/g·°C for iron.
4.Calculate the standard enthalpy of combustion of the transition of C(s, graphite) `->` C(s, diamond), given
C(s, graphite) + `O_2 -> CO_2 DeltaH^0 = -393.5 kJ"/"mol`
`CO_2 -> C(s, diamond) + O_2 DeltaH^0 = + 395.41 kJ"/"mol`
5. 1.150 g of sucrose goes through combustion in a bomb calorimeter. If the temperature rose from 23.42°C to 27.64°C and the heat capacity of the calorimeter is 4.90 kJ/°C, then determine the heat of combustion of sucrose, `C_(12)H_(22)O_(11)`, in kj per mole of `C_(12)H_(22)O_(12)`.
6. Without doing a calculation, predict whether the entropy change will be positive or negative.
a) `C_2H_6(g) + 7/2O_2(g) -> 3H_2O(g) + 2CO_2(g)`
b) `3C_2H_2(g) -> C_6H_6(l)`
c) `C_^H_(12)O_6(s) + 6O_2(g) -> 6CO_2(g) + 6H_2O(l)`
7. Calculate the standard-state free energy of formation for the H2O2(l) from H2 and O2, given the following values:
`DeltaG_f` (`H_2`): 0 kJ/mol
`DeltaG_f` (`O_2`): 0 kJ/mol
`DeltaG_f` (`H_2O_2(l)`): -120.4 kJ/mol
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10. The change in internal energy for the combustion of 1.0 mol of octane at a pressure of 1.0 atm is 5084.3 kJ. If the change in heat energy is 5074.1 kJ, how much work is done during the combustion?
11. The propane fuel (`C_3H_8`) used in gas barbeques burns according to the following thermochemical equation: `C_3H_8(g) + 5O_2(g) -> 3CO_2 (g) + 4H_2O (g)` `DeltaH_(rxn)= -2217 kJ`
If a pork roast must absorb 160 kJ to fully cook, and if only 10% of the heat produced by the BBQ is actually absorbed by the roast, what mass of `CO_2` is emitted into the atmosphere during the grilling of the porkroast?
12. A 5.1g piece of gold jewelry is removed from water at 100.0°C and placed in a coffee-cup calorimeter containing 16.9 g of water at 22.5°C. The equilibrium temperature is 23.2°C. The calorimeter constant is known to be 1.54 J/°C. What is the specific heat of this piece of jewelry? The specific heat of pure gold is 0.129J/g°C. Is the jewelery pure gold?
13. Use the tabulated bond energies to estimate the enthalpy of the following reaction: `CO + H_2O -> CO_2 + H_2`
14. Given the following data calculate the heat of combustion in kJ/mol of xylose, `C_5H_(10)O_5(s)`, used in a bomb calorimetry experiment: mass of `C_5 H_(10) O_5(s) = 1.250 g`, heat capacity of calorimeter = 4.728 kJ/°C, Initial Temperature of the calorimeter = 24.37°C, Final Temperature of calorimeter = 28.29°C.
15. In the following changes is there an increase in entropy?
a) The freezing of water
b) `l_2(s) -> l_2(g)`
c) The sublimation of dry ice, solid `CO_2`
d) `PCl_5 (g) -> PCl_3(g) + Cl_2(g)`
16. Using the standard molar entropies, calculate the value of `DeltaS` for the following reaction:
`4HCl(g) + O_2(g) -> 2Cl_2(g) + 2H_2O(g)` .
17. Consider the following reaction:
`CaCO_3 -> CaO + CO_2`
At what temperature will this reaction become spontaneous? Note: Assume `DeltaH_r^°` and `DeltaS_r^°` are temperature independent. (Hint: What variable tells us for sure whether the reaction is spontaneous or not?)
Given values:
| Substance | `DeltaH_f^°` | `S_f^°` |
| `CaCO_3` | -1206.9 kJ/mol | 92.9 J/K mol |
| `CaO` | -635.6 kJ/mol | 39.8 J/K mol |
| `CO_2` | -393.5 kJ/mol | 213.6 J/K mol |
Subpages (1): Chapter 12 Answers to Problems