Fiducia TogetherReversible reactions and equilibrium
Reactions that go both ways, and how conditions shift the balance.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
A reversible reaction can proceed in both directions. In a closed system it reaches dynamic equilibrium: both reactions continue at equal rates, so concentrations stop changing.
Where it applies
Higher tier GCSE chemistry, and A Level.
How it works
Le Chatelier's principle: if a change is made, the equilibrium shifts to oppose it. Raising temperature favours the endothermic direction; raising pressure favours the side with fewer gas molecules; adding reactant shifts it towards products.
The Haber process is the standard application, and its conditions are a compromise between yield and rate.
How to use it in your work
Dynamic equilibrium means the reactions have NOT stopped. Saying they stop loses the mark.
For the Haber process, explain the compromise: a lower temperature would give more yield but too slowly to be useful.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams. The subject song runs the topics in order.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Chemistry Song The GCSE chemistry specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.