Le Chatelier's Principle
A system at equilibrium shifts to oppose a disturbance.
About this topic
Le Chatelier's principle states that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves that stress. Adding reactant shifts the equilibrium toward products; removing product does the same. Raising pressure favours the side with fewer gas moles; raising temperature favours the endothermic direction.
The stress can be a change in concentration, pressure (volume), or temperature. A catalyst does not shift equilibrium because it speeds up both directions equally. For the Haber process, N2 + 3H2 ⇌ 2NH3 (exothermic), high pressure pushes toward ammonia since there are four moles of gas on the left and two on the right, while a lower temperature would raise the yield but slow the rate, so a compromise of about 450 degrees Celsius and 200 atm with an iron catalyst is used. Ammonia is removed as it forms to keep shifting right.
Example: in a cobalt chloride solution, Co(H2O)6 2+ (pink) + 4Cl- ⇌ CoCl4 2- (blue) + 6H2O. Adding hydrochloric acid turns it blue, while adding water or cooling turns it pink. In blood, the carbon dioxide and bicarbonate buffer responds to changes in the same way.
A common error is thinking the equilibrium constant changes with concentration or pressure; only temperature changes K. Another is expecting the shift to completely cancel the stress; it only partly offsets it.
Key ideas
- Add reactant: shift right
- Raise temperature: favors endothermic direction
- Pressure matters for gases
Quick check
Use cases: where Le Chatelier's Principle helps
- Homework: review the key idea behind Le Chatelier's Principle before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Le Chatelier's Principle without notes.
- Visual learning: play with the interactive lab to see how Le Chatelier's Principle changes when you adjust its inputs.
- Teaching a friend: explain Le Chatelier's Principle in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is Le Chatelier's Principle?
A system at equilibrium shifts to oppose a disturbance.
What will I learn in Le Chatelier's Principle?
Add reactant: shift right. Raise temperature: favors endothermic direction. Pressure matters for gases.
Is Le Chatelier's Principle part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Le Chatelier's Principle lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Le Chatelier's Principle?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.