When solid ammonium chloride dissociates at a certain temperature in a 0.500 dm3 container,

ammonia and hydrogen chloride are formed.

NH4Cl (s) NH3 (g) + HCl (g)

The initial amount of ammonium chloride was 1.00 mol, and when the system had reached

equilibrium there was 0.300 mol of ammonium chloride.

What is the numerical value of Kc for this reaction under these conditions?

1) 0.500 dm3 = 0.5 liter

2) Equilibrium reaction

NH4Cl (s) ⇄ NH3 (g) + HCl (g)

3) Table of changes

Number of moles

Species NH4Cl NH3 HCl

Start 1mol 0 0

Change - 0.7 + 0.7 + 0.7

Equilibrium 0.3 0.7 0.7

4) Equilibrium constant

Kc = [NH3] [HCl]

[NH3] = 0.7 mol / 0.5 liter = 1.4 M

[HCl] = 0.7 mol / 0.5 liter = 1.4 M

Kc = (1.4M) ^2 = 1.96M^2

The numerical value is just 1.96 (without the units)