Fall 2007 CH301 Worksheet 12--Thermodynamics
1. A small (74 g) serving of French fries is burned in a bomb calorimeter containing 3 L of water. The
temperature of the water increases by 82°C. The calorimeter has a heat capacity of 200 J/°C, the density
of water is 1 g/mL, and the heat capacity of water is 4.18 J/g°C. How much heat is evolved per gram of
french fries?
2. The same calorimeter as in number 1 is used to measure the enthalpy of dissolving 2.5 mol of potassium
chloride (KCl) in water. If the enthalpy of the process is ∆H = +15 kJ/mol and the initial temperature of
the water is 298 K, what is the final temperature of the water?
3. Given
C2H2 + 5/2 O2 →2 CO2 + H2O ∆H = -1300 kJ/mol
C2H2 + H2 →C2H4 ∆H = -175 kJ/mol
C2H4 + H2O →CH3CH2OH ∆H = -44 kJ/mol
H2 + ½ O2 →H2O ∆H = -286 kJ/mol
Find ∆H for the combustion of ethanol,
CH3CH2OH + 3 O2 → 2 CO2 + 3 H2O
4. Given the following information, calculate the enthalpy change for the reaction
4 HNO3(l) + 5 N2H4(l) → 7 N2(g) + 12 H2O(l)
∆Hf° (HNO3(l)) = -174.10 kJ/mol
∆Hf° (N2H4(l)) = +50.63 kJ/mol
∆Hf° (H2O(l)) = -285.83 kJ/mol
5. Calculate the free energy change of the same reaction at 298 K, given
Sm° (HNO3(l))= 155.60 J/K•mol
Sm° (N2H4(l))= 121.21 J/K•mol
Sm° (N2(g))= 191.61 J/K•mol
Sm° (H2O(l))= 69.91 J/K•mol
5. Calculate the enthalpy change for the combustion of ethanol using bond energies.
C-H = 412 kJ/mol
C-C = 348 kJ/mol
C-O = 360 kJ/mol
C=O = 743 kJ/mol
O=O = 497 kJ/mol
O-H = 463 kJ/mol
6. Using bond energies, calculate the enthalpy change for the reaction
CH4(g) + 4 Cl2(g) → CCl4(g) + 4 HCl(g)
C-H = 412 kJ/mol
C-Cl = 338 kJ/mol
Cl-Cl = 242 kJ/mol
Cl-H = 431 kJ/mol
7. Use enthalpies of formation to find the enthalpy change for the same reaction.
∆Hf° (CH4(g)) = -74.81 kJ/mol
∆Hf° (CCl4(g)) = -163.78 kJ/mol
∆Hf° (HCl(g)) = -92.31 kJ/mol
8. Find the approximate work done for the following reaction at 400 K.
