Equilibrium Constant — Flashcards & Quiz

Q1: Write the general expression for the equilibrium constant Kc.

For aA + bB ⇌ cC + dD: Kc = [C]^c[D]^d / [A]^a[B]^b. Concentrations are in mol L⁻¹ at equilibrium. Pure solids and pure liquids are excluded from the expression. A large Kc (≫1) means products are favoured; a small Kc (≪1) means reactants are favoured.

Q2: How does the value of Kc relate to the position of equilibrium?

Kc ≫ 1: equilibrium lies far to the right (products favoured). Kc ≈ 1: significant amounts of both reactants and products present. Kc ≪ 1: equilibrium lies far to the left (reactants favoured). Kc is constant at a given temperature — it changes ONLY when temperature changes, not with concentration or pressure changes.

Q3: What is Kp and how does it differ from Kc?

Kp is the equilibrium constant expressed in terms of partial pressures of gaseous species: Kp = (pC)^c(pD)^d / (pA)^a(pB)^b. Units depend on the reaction. Kp is related to Kc by Kp = Kc(RT)^Δn where Δn = moles of gaseous products − moles of gaseous reactants. If Δn = 0, Kp = Kc.

Q4: How does the equilibrium constant change when a reaction equation is reversed or multiplied?

Reversed: K_reverse = 1/K_forward. Multiplied by factor n: K_new = (K_original)ⁿ. Halved: K_new = √K_original. These relationships apply to both Kc and Kp. When combining equations (Hess's law style), multiply the K values.

Q1: The value of Kc changes when the concentration of a reactant is increased.

Answer: FALSE

Kc is constant at a given temperature. Changing concentration shifts the position of equilibrium but does NOT change the value of Kc. Only temperature changes Kc.

Q2: A large Kc value indicates that products are favoured at equilibrium.

Answer: TRUE

When Kc ≫ 1, the numerator (products) is much larger than the denominator (reactants), meaning the equilibrium position favours product formation.

Q3: Pure solids and liquids are included in the Kc expression.

Answer: FALSE

Pure solids and pure liquids have constant concentrations and are excluded from Kc expressions. Only aqueous and gaseous species are included.