CHEMBOOK Chapter 13 Extra Problems

 

  1. State Le Chatelier’s principle as simply and clearly as you can..
  2. Write an expression for the equilibrium constant in terms of partial pressures for each of the following reactions:

a)      NO(g) + ½ O2(g)  NO2(g)

b)      N2O5(g)  2 NO2(g) + ½ O2(g)

c)      BaCO3(s)  BaO(s) + CO2(g)

d)      PCl5(g)  PCl3(g) + Cl2(g)

e)      NH4Cl(s)  NH3(g) + HCl(g)

 

  1. Which of the above equilibria shifts to the right when the volume of the equilibrium mixture is decreased?
  2. Some equilibria shift to the left when the temperature is raised, while others shift to the right. What information do you need to know about a chemical reaction in order to be able to predict which way the equilibrium will move when the temperature is increased?
  3. What is the relative activity of each of the following substances under the stated conditions? Take the standard state to be 100.0 kPa.

a)      O2(g) at a partial pressure of 20.0 kPa.

b)      Cl2(g) at a partial pressure of 5.00 kPa.

c)      NH3(g) at a partial pressure of 4.0 Mpa.

d)      H2O(l) at atmospheric pressure

e)      N2(g) in air at a total pressure of 103.0 kPa; the mole fraction of N2(g) in air is 0.781.

6.      A mixture of N2O4(g) and NO2(g) is at equilibrium. The partial pressures of the two compounds are p(N2O4) = 35.0 kPa and p(NO2) = 65.0 kPa. Calculate the equilibrium constant for the reaction  N2O4(g)  2 NO2(g).

7.      A mixture of N2O4(g) and NO2(g) is at equilibrium at a total pressure of 125.0 kPa. The partial pressure of N2O4(g) is p(N2O4) = 27.3 kPa. Calculate the equilibrium constant for the reaction  N2O4(g)  2 NO2(g).

8.      A mixture of methane CH4(g), steam H2O(g), carbon monoxide CO(g), and hydrogen H2(g) are brought to equilibrium at high temperature in contact with a catalyst. The partial pressures are p(CH4) = 250. kPa, p(H2O) = 300. kPa, p(CO) = 25. kPa and p(H2) = 75. kPa. Calculate the equilibrium constant for the steam reforming reaction CH4(g) + H2O(g)  CO(g) + 3 H2(g). 

9.      The chemical equation for the partial oxidation of methane is

CH4(g) + ½ O2(g)  CO(g) + 2 H2(g)

The equilibrium constant for this reaction at a particular temperature is 5.0´108. Calculate the equilibrium constant for the doubled reaction:

2 CH4(g) + O2(g)  2 CO(g) + 4 H2(g)

10.  Steam and hot carbon are brought to equilibrium at high temperature, and form hydrogen and carbon monoxide according to the reaction

C(s) + H2O(g)  CO(g) + H2(g)

The partial pressures at equilibrium of steam is p(H2O) = 20.0 kPa and the partial pressure of carbon monoxide is p(CO) = 65.0 kPa. What is the partial pressure of H2(g)? What is the equilibrium constant for the reaction at this temperature?

11.  Consider the possible formation of NO(g) in air at high temperature, according to the reaction ½ N2(g) + ½ O2(g)  NO(g). Suppose that air at 100. kPa containing 0.21 mole fraction oxygen and 0.79 mole fraction of nitrogen (and no NO(g) ) is heated without change of pressure. Write an ICE table to show how the partial pressures change when so NO(g) is formed, and write an expression for the equilibrium constant.

12.  (Do no. 11 first) At a certain temperature, well above room temperature, the equilibrium constant for the reaction ½ N2(g) + ½ O2(g)  NO(g) is K = 1.0´10-6. Calculate the equilibrium partial pressure of NO(g) in air at this temperature and a total pressure of 100. kPa.

13.  The equilibrium constant for the reaction N2O4(g)  2 NO2(g) is 0.35 at a particular temperature. Calculate the partial pressure of NO2(g) in an equilibrium mixture if the partial pressure of N2O4(g) is 15.0 kPa.

14.  What is the equilibrium constant for the process H2O(l)  H2O(g) at a temperature at which the vapour pressure of water is 35.78 kPa?

15.  When steam reacts with carbon at high temperature, carbon monoxide CO and hydrogen H2 are formed:

C(s) + H2O(g)  CO(g) + H2(g)

When steam and carbon are brought to equilibrium at a total pressure of 150. kPa, calculate the mole fractions of all gases present in the mixture if the equilibrium constant for the reaction is 2.50.

16.  The enthalpy change of the methanol synthesis reaction

CO(g) + 2 H2(g)  CH3OH(g)

is DH° =  -90.1 kJ/mol. If the equilibrium constant is K = 2.2´104 at 298 K, calculate the value of K at 400. K.

17.  The enthalpy change of the oxidation reaction

SO2(g) + ½ O2(g)  SO3(g)

is DH° =  -98.9 kJ/mol. If the equilibrium constant is K = 2.7´1012 at 298 K, calculate the value of K at 450. K.