Workshop CHE 166
Problem Set #8
1. What mass of potassium chlorate, KClO3, must be decomposed to produce 126 L of oxygen gas at 133 oC and 0.880 atm?
2 KClO3 (s) ® 2 KCl (s) + 3 O2 (g)
2. Cyanogen is a compound of carbon and nitrogen. On combustion is excess oxygen, 500 mL of cyanogen gives 500 mL of N2 and 1000 mL of CO2, all measured at the same temperature and pressure. What is the formula of cyanogen?
3. A sample of zinc metal is allowed to react completely with an excess of hydrochloric acid:
Zn (s) + 2 HCl (aq) ® ZnCl2 (aq) + H2 (g).
The hydrogen gas produced is collected over water at 25.0 oC. The volume of the gas is 7.80 L and pressure is 0.980 atm. Calculate the amount of zinc metal in grams consumed in the reaction. (Vapor pressure of water at 25.0 oC = 23.8 mmHg.)
4. How many liters of chlorine gas at 200 oC and 0.500 atm can be produced by the reaction of 12.0 g of MnO2 with HCl as follows?
MnO2 (s) + 4 HCl (aq) ® MnCl2 (aq) + 2 H2O (l) + Cl2 (g)
5. A mixture of gases contains 4.46 moles of neon, Ne, 0.74 moles argon, Ar, and 2.15 moles of xenon, Xe. Calculate the partial pressures of the gases if the total pressure is 2.00 atm at a certain pressure.
6. It requires 57.1 seconds for 1.42 L of an unknown gas to effuse through a pinhole, and it takes 83.9 seconds for the same volume of N2 gas to effuse at the same temperature and pressure. What is the molar mass of the unknown gas?
7. List the following gases in order of increasing diffusion rates: PH3, ClO2, Kr, NH3, HI. Calculate the ratio of diffusion rates of fastest to slowest.
8. Hydrogen, H2, is burned in oxygen to produce water vapor:
2 H2 (g) + O2 (g) ® 2 H2O (g) D H = - 484 kJ
What is the enthalpy change per gram of hydrogen?
9. Ammonia burns in the presence of a copper catalyst to form nitrogen gas.
4 NH3 (g) + 3 O2 (g) ® 2 N2 (g) + 6 H2O (g) D H = - 1267 kJ
What is the enthalpy change when 25.6 g of ammonia is burned?
10. Hydrogen cyanide is a highly poisonous, volatile liquid. It can be prepared by the reaction
CH4 (g) + NH3 (g) ® HCN (g) + 3 H2 (g).
Using the following thermochemical equations, what is the heat (enthalpy) of reaction for this process?
N2 (g) + 3 H2 (g) ® 2 NH3 (g) D H = - 91.8 kJ
C (s,graphite) + 2 H2 (g) ® CH4 (g) D H = - 74.9 kJ
H2 (g) + 2 C (s,graphite) + N2 (g) ® 2 HCN (g) D H = 270.3 kJ
11. Calculate the enthalpy of reaction for:
H2 (g) + C2H4 (g) ® C2H6 (g)
given the following standard enthalpies of formation at 25 oC:
D Hfo [C2H4(g)] = 52.3 kJ/mol and D Hfo [C2H6 (g)] = - 84.7 kJ/mol.