The Equilibrium Constant, Kc (AQA AS Chemistry): Revision Note

The Equilibrium Constant, Kc

Equilibrium expression & constant

• The equilibrium constant expression is an expression that links the equilibrium constant, K, to the concentrations of reactants and products at equilibrium taking the stoichiometry of the equation into account

• So, for a given reaction:

aA + bB ⇌ cC + dD

• The corresponding equilibrium constant expression is written as:

$\mathit{K}\mathbf{=}\frac{{\left[C\right]}^{\mathbf{c}}{\left[D\right]}^{\mathbf{d}}}{{\left[A\right]}^{\mathbf{a}}{\left[B\right]}^{\mathbf{b}}}$

• Where:

  • [A] and [B] = equilibrium reactant concentrations (mol dm^-3)

  • [C] and [D] = equilibrium product concentrations (mol dm^-3)

  • a, b, c and d = number of moles of corresponding reactants and products

• Solids are ignored in equilibrium constant expressions

• The equilibrium constant, K, of a reaction is specific to a given equation