Consider the reversible reaction.

PCl5↽−−⇀PCl3+Cl2PCl5↽−−⇀PCl3+Cl2

Are the concentrations of phosphorus pentachloride, PCl5,PCl5, and phosphosphorus trichloride, PCl3,PCl3, constant or changing at equilibrium?

a. The concentration of PCl5PCl5 is constant, and the concentration of PCl3PCl3 is changing at equilibrium.
b. The concentration of PCl5PCl5 is changing, and the concentration of PCl3PCl3 is constant at equilibrium.
c. The concentrations of both PCl5PCl5 and PCl3PCl3 are constant at equilibrium.
d. The concentrations of both PCl5PCl5 and PCl3PCl3 are changing at equilibrium.

which one is correct please explain

Option D is correct.

The concentrations of both PCl₅ and PCl₃ are changing at equilibrium

Explanation:

Chemical equilibrium during a reversible chemical reaction, is characterised by an equal rate of forward reaction and backward reaction. It is better described as dynamic equilibrium.

This is because, the concentration of the elements and compounds involved in the reversible chemical reaction at equilibrium changes, but the rate of change of the reactants is always equal to the rate of change of products.

Hence, the concentration of reactants and products, such as PCl₅ and PCl₃ are allowed to change at equilibrium, but alas, the rate of forward reaction must always match the rate of backward reaction for the process to remain in a state of Chemical equilibrium.

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