Chapter 6 Thermochemistry
Homework Problems
1.
2.
The enthalpy change for the fermentation (without oxygen, O2 gas) reaction of glucose to alcohol and carbon dioxide
is –67 kJ.
a.
Write a chemical equation for the fermentation reaction and show how energy is involved in the reaction.
b.
Is the reaction exothermic or endothermic?
c.
Is energy, in the form of heat, absorbed or evolved as the reaction occurs?
The specific heat capacity of graphite is 0.71 J/oC.g. Calculate the energy required to:
a.
Raise the temperature of 1.0 mol graphite by 1.0°C.
b.
Raise the temperature of 850 g graphite by 150°C.
c.
Raise the temperature of 75 kg graphite from 294 K to 348 K.
3.
In a coffee-cup calorimeter, 100.0mL of 1.0 M NaOH and 100.0 mL of 1.0 M HCl are mixed. Both solutions were
originally at 24.6°C. After the reaction, the final temperature is 31.3°C. Assume that all the solutions have a density of
1.0 g/mL and a specific heat capacity of 4.18 J/g.oC.
Calculate the enthalpy change for the neutralization of HCl by NaOH. Assume that no heat is lost to the surroundings or
to the calorimeter.
4.
Camphor (C10H16O) has an energy of combustion of –5903.6 kJ/mol. A sample of camphor with a mass of 0.1204 g is
burned in a bomb calorimeter, the temperature increases by 2.28°C. Calculate the heat capacity of the calorimeter.
A 0.1964 g sample of quinone (C6H4O2) is burned in a bomb calorimeter that has a heat capacity of 1.56 kJ/°C. The
temperature of the calorimeter increases by 3.2°C. Calculate the energy of combustion of quinone per gram and per
mole.
5.
Multi-part more difficult problem. If you follow this problem as a guide you should be able to do the extra credit
exercise on bomb calorimetry (Video Exercise #2).
a.
The combustion of 0.1584 g of benzoic acid increases the temperature of a bomb calorimeter by 2.54 oC.
Calculate the heat capacity of the calorimeter. (The energy released by the combustion (∆E) of benzoic acid is
26.42 kJ/g.)
b.
After finding the heat capacity of the calorimeter, a 0.2130g sample of vanillin (C8H8O3) is then burned in the same
calorimeter. The temperature increased by 3.25°C.
Write a balanced equation for the combustion of vanillin.
What is the change in energy of combustion (∆E) per mole of vanillin?
Calculate the change in enthalpy of combustion per mole (∆H) of vanillin. Utilize the thermodynamics table in the
appendix in your text to aid you in calculating the change in enthalpy of formation per mole (∆Hfo) of vanillin.