Question

Under which circumstances are Kp and Kc equal for the reaction aA(g) + bB(g) ⇌ cC(g) +dD(g)?

-when the reaction is reversible
-when a + b = c +d
-when the equilibrium constant is large

Answer 1

Kp and Kc are equal when the total number of moles of gaseous reactants equals that of gaseous products, corresponding to when a + b = c + d. Reversibility does not influence this, nor does the size of the equilibrium constant.

Step-by-step explanation:

The circumstances under which Kp and Kc are equal for the reaction aA(g) + bB(g) ⇌ cC(g) + dD(g) occur when the total number of moles of gaseous reactants equals the total number of moles of gaseous products, which means when a + b = c + d. This is because Kp and Kc are related by the equation Kp = Kc(RT)Δn, where R is the gas constant, T is the temperature, and Δn is the change in the number of moles of gas (moles of products minus moles of reactants). When Δn is zero, the (RT)Δn term is equal to 1, and therefore Kp = Kc.

This equality does not depend on whether the reaction is reversible or the magnitude of the equilibrium constant. Reversibility is a characteristic of chemical equilibrium but does not directly affect the relationship between Kp and Kc. The magnitude of the equilibrium constant, whether large or small, indicates the relative concentrations of products and reactants at equilibrium but does not determine the equality of Kp and Kc.