Chemistry 12 · Chemistry · Lesson 2.1
Dynamic equilibrium and reversible reactions
- Level
- Grade 12
- Reading time
- 12 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Equal forward and reverse reaction rates.
What is chemical equilibrium?
Short answer
Chemical equilibrium is the state of a reversible reaction in which the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products stay constant over time. It is dynamic — reactions continue in both directions — not static. Le Châtelier’s principle predicts how the equilibrium shifts when conditions change.
Concept preview
What you will be able to do
- 01Explain what a reversible reaction is
- 02Describe how a system reaches equilibrium in terms of rates
- 03Explain why equilibrium is dynamic
- 04State the conditions required for equilibrium
Up to now you have treated most reactions as one-way streets: reactants go in, products come out, and that is the end of it. In reality a great many reactions are two-way. As products build up, they begin to react with one another to reform the original reactants. When the two opposing reactions come into balance, the system reaches a state called chemical equilibrium — one of the central ideas in all of chemistry, and the foundation for everything in this chapter.
School Plan
Dynamic equilibrium and reversible reactions
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Related topics
Frequently asked questions
- What does Le Châtelier’s principle say?
- If a system at equilibrium is disturbed (concentration, pressure, or temperature), it shifts to partly counteract the change.
- Does equilibrium mean the reaction has stopped?
- No — both directions continue at equal rates, so concentrations stay constant while the reaction is still occurring.