Equilibrium Problems

  1. Draw a sketch of an energy vs. reaction path graph for an endothermic reaction. Identify the reactants, products, activation energy, heat of reaction, and where the transition state is.
  2. What effect does a catalyst have on the rate of a reaction? How would it affect the activation energy and why?
  3. A mixture at equilibrium at 827 °C contains 0.552 mol CO2, 0.552 mol H2, 0.448 mol CO, and 0.448 mol H2O.

    CO2   +   H2   <-->   CO   +   H2O

    1. What is the value for Keq at this temperature?
    2. More CO2 is added to the system, which direction will the reaction shift?
    3. What effect did part b) have on the equilibrium constant?
    4. What effect would adding a catalyst have on the equilibrium?
    5. Are the reactants or products favored in this reaction?
  4. How does the equilibrium shift when
    1. the concentration of PCl3 is increased at constant temperature and pressure?
    2. the pressure is decreased?
    3. the concentration of Cl2 is decreased?

    PCl5(g)   <-->   PCl3(g)   +   Cl2(g)

  5. For the following equilibria, explain how the given stress affects the equilibrium point.
    1. N2(g)   +   O2 (g)   <-->   2 NO(g)   Increase in pressure
    2. 2 SO3 (g)   +   Heat   <-->   2 SO2 (g)   + O2 (g)   Increase in Temperature
    3. 2 SO3 (g)   +   Heat   <-->   2 SO2 (g)   + O2 (g)   Increase in Pressure
    4. CaCO3(s)   <-->   CaO(s)   +   CO2(g)   Removal of CO2
  6. Write the Keq expressions for the following expressions.
    1. 2 C2H6 (g)   +   7 O2 (g)   <-->   4 CO2 (g)   +   6 H2O(g)
    2. 4 PH3 (g)   <-->   P4 (g)   +   6 H2O(g)
    3. 4 HCl(g)   +   O2 (g)   <-->   2 Cl2 (g)   +   2 H2O(g)
  7. At a high temperature the following system reaches equilibrium - N2 + O2   <-->   2 NO.
    An analysis of the mixture in a one liter container gives the following results: nitrogen = 0.50 moles, oxygen = 0.50 moles, nitrogen monoxide = 0.020 mol.
    1. Calculate Keq for this system.
    2. At the same temperature, a new system is made with 0.70 moles of each of the reactants. Find the concentration of the NO. (Hint: you can use the same Keq from part a), why?)
  8. If the Keq for the following reaction is 8.2 x 10-2, find the concentration of COCl2 (g) if each product has a concentration of 1.2 x 10-2 M?
    COCl2 (g)   <-->   CO(g)   +   Cl2 (g)
  9. Find the Keq for the reaction if [H2S] = 0.015 M, [H2] = 0.010 M, and the [S2] = 0.051 M.
    2 H2S(g)   <-->   2 H2 (g)   +   S2 (g)
  10. In a 1.00 L container, 1 mole of SO3 is decomposed. At equilibrium, 0.300 mole of O2 is present. Calculate the concentrations of SO2 and SO3 at equilibrium, and calculate Keq.
    2 SO3 (g)   <-->   2 SO2 (g)   + O2 (g)



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