Find and fix the mistake in the equilibrium expression. PCl5(g) ⇌ PCl3(l) + Cl2(g) Kc = [Cl2]/[PCl5]

Verified step by step guidance

1. insert step 1> Identify the chemical reaction given: PCl5(g) ⇌ PCl3(l) + Cl2(g).
2. insert step 2> Recall that the equilibrium constant expression, Kc, is based on the concentrations of the gaseous and aqueous species involved in the reaction.
3. insert step 3> Note that PCl3 is in the liquid state, and pure liquids and solids do not appear in the equilibrium expression.
4. insert step 4> Write the correct equilibrium expression for the reaction: Kc = [Cl2]/[PCl5].
5. insert step 5> Verify that the expression only includes the gaseous species, which are Cl2 and PCl5.

Key Concepts

Equilibrium Expression

The equilibrium expression is a mathematical representation of the concentrations of reactants and products at equilibrium. It is derived from the balanced chemical equation and reflects the ratio of product concentrations to reactant concentrations, each raised to the power of their coefficients. For gaseous and aqueous species, concentrations are used, while solids and liquids are omitted from the expression.

Phase of Substances in Equilibrium

In equilibrium expressions, only gases and aqueous solutions are included, while solids and liquids are excluded. This is because the concentration of pure solids and liquids does not change during the reaction and does not affect the equilibrium position. In the given reaction, PCl3 is a liquid, so it should not appear in the equilibrium expression.

Correct Form of Kc

The correct form of the equilibrium constant Kc for the reaction PCl5(g) ⇌ PCl3(l) + Cl2(g) should only include the gaseous species. Therefore, the correct expression is Kc = [Cl2]/[PCl5]. The presence of PCl3 in the original expression is incorrect, as it is a liquid and should not be included in the equilibrium constant calculation.