Which statement is true about Kp?

Which statement is true about Kp?

• A. It is the equilibrium constant expressed in terms of pressure
• B. It is the rate constant
• C. It is the equilibrium constant expressed in terms of concentration
• D. It is independent of temperature

Answer: (A)

Kp represents the equilibrium constant written in terms of the partial pressures of gases. In gas-phase equilibria, the activities of the species are related to their partial pressures, so the equilibrium expression uses p for products raised to their stoichiometric powers divided by the same for reactants. This is different from Kc, which uses concentrations instead of pressures. The two are connected by Kp = Kc (RT)^{Δn}, where Δn is the change in the number of moles of gas. Temperature matters because changing temperature shifts the position of equilibrium, altering the value of Kp (and Kc) accordingly. It isn’t a rate constant, and it isn’t independent of temperature.

Kp represents the equilibrium constant written in terms of the partial pressures of gases. In gas-phase equilibria, the activities of the species are related to their partial pressures, so the equilibrium expression uses p for products raised to their stoichiometric powers divided by the same for reactants. This is different from Kc, which uses concentrations instead of pressures. The two are connected by Kp = Kc (RT)^{Δn}, where Δn is the change in the number of moles of gas. Temperature matters because changing temperature shifts the position of equilibrium, altering the value of Kp (and Kc) accordingly. It isn’t a rate constant, and it isn’t independent of temperature.