Chemical Equilibrium

Le Chatelier's principle, equilibrium constant

Chemical Equilibrium

Equilibrium: forward rate equals reverse rate, concentrations remain constant. Le Chatelier's principle: if a system at equilibrium is disturbed, it shifts to counteract the change. Kc = [products]/[reactants].

Example

Applying Le Chatelier

N2 + 3H2 <-> 2NH3 (exothermic). Increase [N2]: shifts right, more NH3. Increase temperature: shifts left, less NH3 (favours endothermic direction). Increase pressure: shifts right (4 mol gas -> 2 mol gas).

Note

Exam Tip

A catalyst does NOT shift equilibrium position — it only speeds up reaching equilibrium. When calculating Kc, only include gaseous and aqueous species. Large Kc means products favoured.

Key Vocabulary

Chemical equilibriumWhen forward and reverse reaction rates are equal and concentrations are constant

Le Chatelier's principleA system at equilibrium will shift to counteract any imposed change

Equilibrium constantThe ratio of product to reactant concentrations at equilibrium

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Chemical equilibrium

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