PLEASE HELP! Consider the reactions of cadmium with the thiosulfate anion.

Question

Cd2 (aq) S2O32-(aq) <==> Cd(S2O3)(aq); K1 = 8.3 ´ 103

Cd(S2O3)(aq) S2O32-(aq) <==> Cd(S2O3)22-(aq); K2 = 2.5 ´ 102

What is the value for the equilibrium constant for the following reaction?

Cd2 (aq) 2S2O32-(aq) Cd(S2O3)22-(aq)

A. 0.030

B. 33

C. 8.1 x 10 3

D. 8.6 x 10 3

E. 2.1 x 10 6

Answer 1

The equilibrium constant for the _sum_ of two reaction is the _product_ of the equilibrium constants of the two reactions. This can be proven mathematically by examining the mass action expression. Since the given reaction is merely a combination of the first two reactions, the equilibrium constant is 8.3×10^3 * 2.5×10^2 ~ 2.1×10^6. The answer is E.