Chapter 14, Problem 14.17QP

Chemical Equilibrium I

Part 1: You run the chemical reaction $\text{C}(aq)+\text{D}(aq)\stackrel{}{\rightleftharpoons }\text{2E}(aq)$ at 25°C. The equilibrium constant K_c for the reaction at this temperature is 2.0.

1. a Write the equilibrium-constant expression for the reaction.
2. b Can you come up with some possible concentrations of C, D, and E that you might observe when the reaction has reached equilibrium at 25°C? What are these values?
3. c A student says that only a very limited number of concentrations for C, D, and E are possible at equilibrium. Is this true? State why you think this is true or is not true.
4. d If you start with 1.0 M concentrations of both C and D and allow the reaction to come to equilibrium, would you expect the concentration of C to have decreased to zero? If not, what would you expect for the concentration of C? (An approximate value is fine.)

Part 2: Consider the reaction $\text{A}(aq)\stackrel{}{\rightleftharpoons }\text{F}(aq)+\text{ G}(aq)$, whose equilibrium constant is 1.0 × 10⁻⁵ at 20°C. For each of the situations described below, indicate whether any reaction occurs. If reaction does occur, then indicate the direction of that reaction and describe how the concentrations of A, B, F, and G change during this reaction.

1. a A(aq) and B(aq) are mixed together in a container.
2. b F(aq) and G(aq) are mixed together in a container.
3. c A(aq) and F(aq) are mixed together in a container.
4. d B(aq) and G(aq) are mixed together in a container.
5. e Just B(aq) is placed into a container.
6. f Just G(aq) is placed into a container.

Consider any one of these situations in which a reaction does occur. At equilibrium, does the reaction mixture have appreciably more products than reactants? If not, how would you describe the equilibrium composition of the reaction mixture? How did you arrive at this answer?