A 0.750 M sample of phosphorus pentachloride decomposes to give phosphorus trichloride and chlorine gases. If the equilibrium concentration of PCl5 is 0.650M, what is the equilibrium constant for the reaction? PCl5(g) > PCl3(g)+ Cl₂(g)
A) Keq = 0.0133
B) Keq = 0.0154
C) Keq = 0.133
D) Keq = 0.154
E) Keq = 65.0

Explanation:

Amount of phosphorus pentachloride reacted = 0.75 M - 0.65 M = 0.10 M

PCl₅(g) > PCl₃(g)+ Cl₂(g)

1 mole               1 mole      1 mole

Amount of phosphorus pentachloride reacted = 0.75 M - 0.65 M = 0.10 M

PCl₃(g) and  Cl₂(g) formed are .10 M and .10 M

Keq = [ PCl₃] x [ Cl₂ ] / [ PCl₅ ]

= .10 M x .10 M / .65 M

= .0154

B ) is the correct choice .