Chemistry 12 · Chemistry · Lesson 2.5
The equilibrium constant
- Level
- Grade 12
- Reading time
- 11 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Writing and interpreting Keq.
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.
Concept preview
What you will be able to do
- 01Write an equilibrium expression from a balanced equation
- 02Interpret the magnitude of Keq
- 03Use the reaction quotient Q to predict the direction of reaction
Every equilibrium is summarised by a single number, the equilibrium constant Keq, which captures the balance point of the reaction. You construct its expression directly from the balanced equation: put the product concentrations in the numerator and the reactant concentrations in the denominator, and raise each concentration to the power of its coefficient. For the general reaction , the expression is .
School Plan
The equilibrium constant
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Related topics
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.