Which statement about Kc and Kp is true?

Which statement about Kc and Kp is true?

• A. They are always equal at the same temperature
• B. They are the same constant
• C. They measure different things (Kc uses concentration, Kp uses pressure)
• D. They are independent of temperature

Answer: (C)

Kc and Kp are two ways to describe the same chemical equilibrium for gases, but they express it in different quantities. Kc uses concentrations (moles per liter) while Kp uses the partial pressures of the gases. Because of this difference, they are not the same constant. They’re connected by the relation Kp = Kc (RT)^{Δn}, where Δn is the change in moles of gas from reactants to products. This means the numerical values depend on temperature (and the reaction’s Δn). They would be equal only in a special case where there’s no net change in gas moles (Δn = 0) or when units cancel the RT factor. So the true statement is that they measure different representations of the same equilibrium (concentration vs pressure), and they’re related but not universally equal or temperature-independent.

Kc and Kp are two ways to describe the same chemical equilibrium for gases, but they express it in different quantities. Kc uses concentrations (moles per liter) while Kp uses the partial pressures of the gases. Because of this difference, they are not the same constant. They’re connected by the relation Kp = Kc (RT)^{Δn}, where Δn is the change in moles of gas from reactants to products. This means the numerical values depend on temperature (and the reaction’s Δn). They would be equal only in a special case where there’s no net change in gas moles (Δn = 0) or when units cancel the RT factor. So the true statement is that they measure different representations of the same equilibrium (concentration vs pressure), and they’re related but not universally equal or temperature-independent.