THERMOCHEMISTRY AND THERMODYNAMICS PROBLEMS
Energy and Work
1. Calculate ΔE for each of the following cases
a. q= + 51 kJ; w= -15 kJ
b. q= +100 kJ; w= -65 kJ
c. q= -65 kJ; w= -20 kJ
d. q = -47 kJ; w= +88 kJ
e. In which of these cases does the system do work on the surroundings?
2. A system releases 125 kJ of heat while 104 kJ of work is done on it. Calculate Δ E for the process.
3. A system absorbs 82 kJ of heat while 47 kJ of work is done on it. Calculate ΔE for the process.
4. A system undergoes a process consisting of the following two steps:
Step 1: The system absorbs 72 J of heat while 35 J of work is done on it
Step 2: The system absorbs 35 J of heat while performing 72 J of work
Calculate E for the overall process.
5. The volume of an ideal gas is decreased from 5.0 L to 5.0 mL at a constant pressure of 2.0 atm. Calculate the work associated with this process.
6. Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 40. Cm3. If the combustion of this mixture releases 950. J of energy, to what volume will the gases expand against a constant pressure of 650. torr if all the energy of combustion is converted into work to push back the piston?
Endothermic and exothermic reactions
1. NO is a component of air pollution that is formed by the following reaction:
N2 (g) + O2 (g) 2NO (g) Δ H = +180 kJ
Why are high temperatures needed to convert N2 and O2 to NO?
2. The reaction SO3 (g) + H2O (l) H2SO4 (aq) is the last step in the commercial production of sulfuric acid. The ΔH for the reaction is -227 kJ. In designing a sulfuric acid plant, is it necessary to provide for heating or cooling of the reaction mixture? Explain
3. Are the following processes endothermic or exothermic?
a. When solid KBr is dissolved in water, the solution gets colder.
b. Natural gas (CH4) is burned in a furnace.
c. When concentrated H2SO4 is added to water, the solution gets very hot.
d. Water is boiled in a teakettle.
e. The combustion of gasoline in a car engine
f. Water condensing on a cold pipe
g. F2 (g) 2F (g)
ENTHALPY
4. The overall reaction in commercial heat packs can be represented as:
4Fe (s) + 3O2 (g) 2Fe2O3 (s) ΔH= -1652 kJ
a. How much heat is released when 4.00 mol of iron is reacted with excess O2?
b. How much heat is released when 1.00 mol Fe2O3 is produced?
c. How much heat is released when 1.00 g of iron is reacted with excess O2?
d. How much heat is released when 10.0 g Fe and 2.00 g O2 are reacted?
5. Consider the following reaction:
2H2 (g) + O2 (g) 2H2O (l) ΔH = -572 kJ
a. How much heat is evolved for the production of 1.00 mol of H2O (l)?
b. How much heat is evolved when 4.03 g of hydrogen is reacted with excess oxygen?
c. How much heat is evolved when 186 g of oxygen is reacted with excess hydrogen?
d. The total volume of hydrogen needed to fill the Hindenburg was 2.0 x 10 8 L at 1.0 atm and 25° C. How much heat was evolved when the Hindenburg exploded, assuming all of the hydrogen reacted?
6. Consider the following reaction: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) ΔH = -891 kJ
Calculate the enthalpy change in the following cases:
a. 1.00 g of methane is burned in excess oxygen
b. 1000. L methane gas at 740. Torr and 25 °C is burned in excess oxygen.
HEAT CAPACITY AND CALORIMETRY
7. It takes 78.2 J to raise the temperature of 45.6 g lead by 13.3°C. Calculate the specific heat capacity and molar heat capacity of lead.
8. A 150.0 g sample of a metal at 75.0 C is added to 150.0 g of H2O at 15.0 °C. The temperature of the water rises to 18.3 °C. Calculate the specific heat capacity of the metal, assuming that all the heat lost by the metal is gained by the water.
9. A 110. g sample of copper (specific heat capacity = 0.20 J/ g°C) is heated to 82.4 °C and then placed in a container of water at 22.3 °C. The final temperature of the water and copper is 24.9 °C. What is the mass of the water in the container, assuming that all the heat lost by the copper is gained by the water?
10. In a coffee cup calorimeter, 50.0 mL of 0.100 M AgNO3 and 50.0 mL of HCl are mixed to yield the following reaction:
Ag + (aq) + Cl – (aq) AgCl (s)
The two solutions were initially at 22.60 °C, and the final temperature is 23.40 °C. Calculate the heat that accompanies the reaction in kJ/mol of AgCl formed. Assume that the combined solution has a mass of 100.0 g and a specific heat capacity of 4.18 J/ g °C
11. In a coffee cup calorimeter, 1.60 g of NH4NO3 is mixed with 75.0 g of water at an initial temperature of 25.00 C. After the dissolution of the salt, the final temperature of the calorimeter contents is 23.34 °C. Assuming the solution has a heat capacity of 4.18 J/ g °C, and assuming no heat loss to the calorimeter, calculate the enthalpy change for the dissolution of NH4NO3 in units of kJ/mol.
12. Consider the dissolution of CaCl2 according to the following equation:
CaCl2 (s) Ca 2+(aq) + 2Cl – (aq) ΔH = -81.5 kJ
An 11.0 g sample of CaCl2 is dissolved in 125 g of water, with both substances at 25.0 °C. Calculate the final temperature of the solution assuming no heat lost to the surroundings and assuming the solution has a specific heat capacity of 4.18 J/ g °C.
13. Consider the following reaction:
2HCl (aq) + Ba(OH)2 (aq) BaCl2 (aq) + 2H2O (l) ΔH= -118 kJ
Calculate the heat when 100. mL of 0.500 M HCl is mixed with 300.0 mL of 0.100 M Ba(OH)2. Assuming that the temperature of both solutions was initially 25.0 °C and that the final mixture has a mass of 400.0 g and a specific heat capacity of 4.18 J/g °C , calculate the final temperature of the mixture.
14. The combustion of 0.1584 g benzoic acid increases the temperature of a bomb calorimeter by 2.54°C. Calculate the heat capacity of this calorimeter. The energy released by combustion of benzoic acid is 26.42 kJ/g. A 0.2130 g sample of vanillin (C8H8O3) is then burned in the same calorimeter, a nd the temperature increases by 3.25 °C. What is the energy of combustion per gram of vanillin? Per mole of vanillin?
15. 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.
HESS’S LAW
16. Given the following data
N2(g) + 2O2 (g) 2NO2 (g) ΔH= 67.7 kJ
N2 (g) + 2O2 (g) N2O4 (g) ΔH = 9.7 kJ
Calculate ΔH for the dimerization of NO2
2NO2 (g) N2O4 (g)
17. Given the following data
NH3 (g) ½ N2 (g) + 3/2 H2 (g) ΔH = 46 kJ
2H2 (g) + O2 (g) 2H2O (g) ΔH= -484 kJ
Calculate ΔH for the reaction
2N2 (g) + 6H2O (g) 3O2 (g) + 4NH3 (g)
18. Given the following data
2O3 (g) 3O2 (g) ΔH = -427 kJ
O2 (g) 2O (g) ΔH = + 495 kJ
NO(g) + O3 (g) NO2 (g) + O2 (g) Δ H= -199 kJ
Calculate ΔH for the reaction
NO(g) + O (g) NO2 (g)
19. The bombardier beetle uses an explosive discharge as a defensive measure. The chemical reaction involved is the oxidation of hydroquinone by hydrogen peroxide to produce quinone and water.
C6H4(OH)2 (aq) + H2O2 (aq) C6H4O2 (aq) + 2H2O (l)
Calculate ΔH for this reaction from the following data
C6H4(OH)2 (aq) C6H4O2 (aq) + H2 (g) ΔH = +177.4 kJ
H2(g) + ½ O2 (g) H2O (g) ΔH = -241.8 kJ
H2 (g) + O2 (g) H2O2 (aq) ΔH= -191.2 kJ
H2O (g) H2O (l) ΔH = -43.8 kJ
20. Given the following data
H2(g) + ½ O2 (g) H2O (l) ΔH = -285. 8 kJ
N2O5 (g) + H2O (l) 2HNO3 (l) ΔH = -76.6 kJ
½ N2 (g) + 3/2 O2 (g) + ½ H2 (g) HNO3 (l Δ H= -174.1 kJ
Calculate H for the reaction
2N2 (g) + 5O2 (g) 2N2O5
21. Given the following data
P4 (s) + 6Cl2 (g) 4PCl3 (g) ΔH= -1225.6 kJ
P4 (s) + 5O2 (g) P4O10 (s) ΔH= -2967.3 kJ
PCl3 (g) + Cl2 (g) PCl5 (g) ΔH = -84.2 kJ
PCl3 (g) + ½ O2 (g) Cl3PO (g) ΔH= -285.7 kJ
Calculate ΔH for the reaction P4O10 (s) + 6 PCl5 (g) 10 Cl3PO(g)
22. Use the values of ΔHf from the chart to calculate ΔH for the following reactions
a. Ca3(PO4)2 (s) + 3H2SO4 (l) 3CaSO4 (s) + 2H3PO4 (l)
b. SiCl4 (l) + 2H2O (l) SiO2 (s) + 4HCl (g)
c. MgO (s) + H2O (l) Mg(OH)2 (s)
d. NH3 (g) + HCl (g) NH4Cl (s)
23. CalculateΔ H for each of the following reactions using the table
4Na (s) + O2 (g) 2Na2O (s)
2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g)
2Na (s) + CO2 (g) Na2O (s) + CO (g)
Explain why water or carbon dioxide fire extinguisher might not be effective in putting out a sodium fire.
24. The reusable booster rockets of the space shuttle use a mixture of aluminum and ammonium perchlorate as fuel. A possible reaction is 3Al(s) + 3NH4ClO4 (s) Al2O3 (s) + AlCl3 (s) + 3NO (g) + 6 H2O (g)
Calculate ΔH for this reaction.
25. The space shuttle orbiter utilizes the oxidation of methyl hydrazine by nitrogen tetroxide for propulsion:
4N2H3CH3 (l) + 5N2O4 (l) 12 H2O(g) + 9 N2 (g) + 4CO2 (g)
26. Consider the reaction:
2ClF3 (g) + 2NH3 (g) N2 (g) + 6HF (g) + Cl2 (g) ΔH= -1196 kJ
Calculate ΔHf for ClF3 (g)
27. The standard enthalpy of combustion of ethene gas, C2H4 (g) is -1411.1 kJ/mol at 298 K. Given the following enthalpies of formation, calculate ΔHf for C2H4 (g) .