Calculate K from Equilibrium Concentrations: Heterogeneous

Question

The equilibrium constant, K_c , for the following reaction is 5.10×10^-6 at 548 K.

NH₄Cl(s) NH₃(g) + HCl(g)

If an equilibrium mixture of the three compounds in a 6.11 L container at 548 K contains 2.99 mol of NH₄Cl(s) and 0.307 mol of NH₃, the number of moles of HCl present is _______ moles.

Answer 1

NH₄Cl(s) <==> NH₃(g) + HCl(g)

[NH₃] = 0.307 mol/6.11 L = 0.050 M

Kc = 5.10x10^-6 = [NH₃][HCl]

5.10x10^-6 = (0.050 M)(x)

x = [HCl] = 1x10^-4 M

moles HCl = 1x10^-4 mol/L x 6.11 L = 6.23 moles