CHEM1312H - The Equilibrium Constant and Reaction Quotient

main rule

if the chemical equation is modified, the equilibrium constant for the equation is modified in the same way

example constant for understanding

-equation: A + 2B ⇌ 3C

-K = [C]³/[A][B]²

modification 1

-if you reverse the chemical equation, the equilibrium constant must be inverted

-equation: 3C ⇌ A + 2B

-K = [A][B]²/[C]³

-rule: K_reverse = 1/K_forward

modification 2

-if we multiply the coefficient in the equation by a factor, we raise the equilibrium constant by same factor

-equation: nA + 2nB ⇌ 3nC

-K^’ = ([C]³/[A][B]²)

-rule: K^’ = Kⁿ

modification 3

-if we add two or more individual chemicals equations to obtain an overall equation, we multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant

-equation: A ⇌ 2B, K₁ = [B]₂/[A]; 2B ⇌ 3C, K₂ = [C]³/[B]²

-sum of two equations: A ⇌ 3C, K_overall = [C]³/[A]

-rule: K_overall = K₁ + K₂