A2 (g) + B2 (g) ⇋ 2 AB (g) Kc is 116.4, initial concentrations are: [A2] = 0.200 M, [B2] = 0.200 M, [AB] = 0.270, what will be the equilibrium concentration of AB (in M)?

Question

Consider the following equilibrium:

A₂ (g) + B₂ (g) ⇋ 2 AB (g)

If the value of K_c for this reaction is 116.4, and the initial concentrations of each species are: [A₂] = 0.200 M, [B₂] = 0.200 M, [AB] = 0.270, what will be the equilibrium concentration of AB (in M)?

Answer 1

A2 + B2 <---> 2AB

0.2.....0.2.........0.270......Initial

-x......-x...........+2x.........Change

0.2-x...0.2-x.....2x..........Equilibrium

Kc = 116.4 = [AB]² / [A2][B2]

116.4 = (2x)² / (0.2-x)(0.2-x)

116.4 = 4x² / x2 - 0.4x + 0.4

Solve for x: I get x = ~0.2

Thus, [AB] @ equilibrium = 2x = 0.4 M