Combining Equilibrium Constants.

It is possible to predict the equilibrium constant of a reaction by combining two or more reactions for which the value of K is known. When combining equilibrium constants, it is important to note the following:

When a reaction is reversed, its Kvalue is inverted; that is, Kreverse=1/Kforward.

When the coefficients of a reaction are multiplied by a factor, the Kvalue is raised to the power of that factor.

When reactions are added, their Kvalues are multiplied.

Part A

Determine the value of the equilibrium constant, Kgoal, for the reaction

N2(g)+H2O(g)⇌NO(g)+12N2H4(g), Kgoal=?

by making use of the following information:

1. N2(g)+O2(g)⇌2NO(g), K1 = 4.10×10−31
2. N2(g)+2H2(g)⇌N2H4(g), K2 = 7.40×10−26
3. 2H2O(g)⇌2H2(g)+O2(g), K3 = 1.06×10−10
Part B

Determine the equilibrium constant, Kgoal, for the reaction

4PCl5(g)⇌P4(s)+10Cl2(g), Kgoal=?

by making use of the following information:

P4(s)+6Cl2(g)⇌4PCl3(g), K1=2.00×1019

PCl5(g)⇌PCl3(g)+Cl2(g), K2=1.13×10−2