MCQ Detailed View

Equilibrium constants describe the ratio of products to reactants at equilibrium. Kc is the equilibrium constant expressed in terms of molar concentrations, while Kp is expressed in terms of partial pressures for gaseous reactions. The relationship between Kp and Kc depends on the change in the number of moles of gas during the reaction.

For the reaction 2HI → H₂ + I₂, the total number of gas molecules on the reactant side is 2 (HI molecules), and on the product side it is 2 (1 H₂ + 1 I₂). The difference in moles of gas, Δn, is calculated as Δn = moles of gaseous products − moles of gaseous reactants = 2 − 2 = 0.

The relationship between Kp and Kc is given by Kp = Kc(RT)^Δn, where R is the gas constant and T is temperature in Kelvin. Since Δn = 0, (RT)^0 = 1, which means Kp = Kc. This is a direct consequence of there being no change in the total number of moles of gas during the reaction.

This principle applies to other reactions as well. When Δn > 0, Kp > Kc, and when Δn < 0, Kp < Kc. For reactions with equal moles of gas on both sides, the equilibrium constants in terms of concentration and pressure are identical.

Understanding the relationship between Kp and Kc is fundamental in physical chemistry, especially in gas-phase equilibria, chemical thermodynamics, and industrial chemical processes. It allows chemists to calculate concentrations, pressures, and predict reaction behavior under different conditions.