Calculate K for Rearranged Equation

Question

The equilibrium constant, K_c, for the following reaction is 5.56×10^-2 at 541 K.

PCl₅(g) PCl₃(g) + Cl₂(g)

Calculate K_c at this temperature for:

PCl₃(g) + Cl₂(g) PCl₅(g)

K_c = 

Answer 1

The equation to be calculated is the reverse of the given equation. Whenever you reverse an reaction, as is the case here, the K for the reversed reaction is the reciprocal of the original K. So, in this case we have...

PCl5 <==> PCl3 + Cl2 K = 5.56x10^-2

PCl3 + Cl2 <==> PCl5 K = 1/5.56x10^-2 = 17.98 = 18.0