Question

Consider 1.70 mol of carbon monoxide and 2.60 mol of chlorine sealed in a 6.00 L container at 476 ^oC. The equilibrium constant, K_c, is 2.50 (in M^-1) for

CO(g) + Cl₂(g) ? COCl₂(g)

Calculate the equilibrium molar concentration of CO.

Answer 1

a = degree of dissociation

        CO(g)       +       Cl2(g)   =        COCl2(g)
Initial:       [CO]0 = 1.7;        [Cl2]0 = 2.6;       [COCl2] = 0
Change:        [CO]0 = -1.7*a ;    [Cl2]0 =-1.7*a;     [COCl2] = 1.7*a
Equilibrium in moles:   [CO]eq = 1.7*(1-a); [Cl2]eq =2.6-1.7*a ; [COCl2]eq =1.7*a
Equilibrium in molarity M:   [CO]eq = 1.7*(1-a)/6; [Cl2]eq = (2.6-1.7*a)/6 ; [COCl2]eq =1.7*a/6

Kc = [COCl2]eq /([CO]eq*[Cl2]eq) = 2.5
1.7*a/6 /(1.7*(1-a)/6*(2.6-1.7*a)/6 ) = 2.5

1.7*a /(1.7*(1-a)*(2.6-1.7*a) ) = 2.5/6
a = 0.44
Equilibrium in molarity M:   [CO]eq = 1.7*(1-a)/6 = 0.16M