Grade 12 · Chemistry
The equilibrium constant
Why it matters
Writing and interpreting Keq.
Advanced20m readingPrerequisite: Entropy change versus enthalpy change
What is the equilibrium constant (Keq)?
Short answer
The equilibrium constant, Keq, describes the ratio of products to reactants at equilibrium for a reversible reaction. It equals the product concentrations divided by the reactant concentrations, each raised to its coefficient in the balanced equation. A large Keq means products are favoured; a small Keq means reactants are favoured. Keq depends only on temperature.
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Frequently asked questions
- What does a large Keq tell you?
- That at equilibrium the reaction lies far toward the products — they dominate the mixture.
- Does Keq change with concentration?
- No. Keq changes only with temperature; adding reactants or products shifts the position of equilibrium but not the constant.