How to Calculate Equilibrium Constant Kc
What is Equilibrium Constant Kc?
The equilibrium constant (Kc) quantifies the ratio of product to reactant concentrations at equilibrium for a reversible reaction. Kc > 1 means products are favoured; Kc < 1 means reactants are favoured.
Step-by-Step Guide
- 1Write the balanced equation
- 2Kc = [Products]^coefficients / [Reactants]^coefficients
- 3Solids and pure liquids are excluded (activity = 1)
- 4Reaction quotient Q compared to Kc tells direction of reaction
Worked Examples
Input
N₂ + 3H₂ ⇌ 2NH₃ at equilibrium: [N₂]=0.1, [H₂]=0.2, [NH₃]=0.5M
Result
Kc = [0.5]²/([0.1][0.2]³) = 312.5
Large Kc → strong product favour
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