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 7.66 L container at 548 K contains 3.58 mol of NH₄Cl(s) and 0.498 mol of NH₃, the number of moles of HCl present is  _______moles.

Answer 1

NH₄Cl(s) <===> NH₃(g) + HCl(g)

Keq = [NH₃] [ HCl] (note: NH₄Cl is not included because it is a solid and solids are not included in Keq)

[NH3] = 0.498 mol / 7.66 L = 0.0650 M

[HCl] = ? M

5.10x10^-6 = (0.0650)(HCl)

[HCl] = x7.85x10^-5 M

moles HCl = 7.85x10-5 moles/L x 7.66 L = 6.0x10^-4 moles