Question

Consider the reaction. PCl5(g)↽−−⇀PCl3(g)+Cl2(g) K=0.042 The concentrations of the products at equilibrium are [PCl3]=0.18 M and [Cl2]=0.30 M . What is the concentration of the reactant, PCl5, at equilibrium?

Answer 1

Answer: The equilibrium concentration of $PCl_5$ is 1.285 M.

Explanation:

The chemical equation for the decomposition of phosphorus pentachloride follows:

$PCl_5(g)\rightleftharpoons PCl_3(g)+Cl_2(g)$

The expression for equilibrium constant is given as:

$K_c=\frac{[PCl_3][Cl_2]}{[PCl_5]}$

We are given:

$K_c=0.042$

$[PCl_3]=0.18M$

$[Cl_2]=0.30M$

The concentration of solid substances are taken to be 1. Thus, they do not appear in the equilibrium constant expression.

Putting values in above equation, we get:

$0.042=\frac{0.18\times 0.30}{[PCl_5]}$

$[PCl_5]=1.285$

Hence, the equilibrium concentration of $PCl_5$ is 1.285 M.