Calculating Equilibrium Constants for Gas-Phase Reactions

[Soaring Crane]

a. If the equilibrium concentration of AB3 is 1.5600 mol/L, and the equilibrium concentration of B2 is 0.3300 mol/L, determine the equilibrium constant for this reaction.

2AB3 (g) <-> A2 (g) + 3B2 (g)


Well, K_c = [B2]^3[A2]/[AB3]^2

[B2] = 0.3300 M
[AB3] = 1.5600 M
[A2] = ?

[A2] = 0.3300 M B2 (1 mol A2/3 mol B2) = 0.11 M ?

K_c = [0.330 M]^3[0.11 M]/[1.5600 M]^2 = 1.624E-3 ??


b. If the initial concentration of AB3 is 0.6300 mol/L, and the equilibrium concentration of A2 is 0.14600 mol/L, determine the equilibrium constant for this reaction.

2AB3 (g) <-> A2 (g) + 3B2 (g)

Once again, K_c = [B2]^3[A2]/[AB3]^2

But
[B2] = 0.14600 M A2 * (3 mol B2/ 1 mol A2) = 0.4380 M
[AB3] = 0.14600 M A2 *(2 mol AB3/ 1 mol A2) = 0.292 M
so 0.6300 M - 0.292 M = 0.338 M
[A2] = 0.14600 M

K_c = [0.14600 M][0.4380 M]^3/[0.3380 M]^2 = 1.074E-1 ?

Thanks.

 

[ksinclair13]

They are both correct I believe.