Question

A student was studying the reaction 2 A ⇄ B. He started with a 0.50 M solution of A. After allowing the system to come to equilibrium, he found that [A] = 0.020 M.

a) What is the equilibrium concentration of B?

b) Determine the equilibrium constant for this reaction.

c) In a second reaction, he started a mixture containing [A]init = 0.30 M and [B]init = 0.050 M. What would be the equilibrium constant in this experiment?

Answer 1

[A]_initial = 0.50M, let x= concentration of B at equilibrium

hence, at equilibrium [A] =0.50-2x, [B] =x

given 0.50-2x= 0.02

2x= 0.5-0.02= 0.48, x= 0.48/2=0.24

[A] =0.5-2*0.24= 0.02, [B] =0.24

K= equilibrium constant = [B]²/[A]=0.24*0.24/0.02=2.88

3. In a second reaction, he started a mixture containing [A]init = 0.30 M and [B]init = 0.050 M. What would be the equilibrium constant in this experiment?

[A]initial =0.3, [B]initial =0.24

let x =concentration change of B to reach equilibrium

hence at equilibrium [A] =0.3-2x, [B] =0.24+x

K= equilibrium constant for the reaction remains the same and is a function of only temperature. Hence K= 2.88