Le Chatelier’s Principle, explained.
Le Chatelier’s principle describes the direction in which an equilibrium system responds to a disturbance under specified conditions.
Why it happens
For a one-to-one fixed-volume A ⇌ B reaction, Q = B/A and equilibrium requires Q = K. Adding material changes total mass; equilibration then conserves A + B and sets B/A to the selected K.
Le Chatelier’s principle describes the direction in which an equilibrium system responds to a disturbance under specified conditions.
Read the result
The direction label comes from comparing Q with K; equilibrating changes composition while preserving the current total A plus B.
A worked example
Add reactant to a balanced vessel
Begin with fifty A and fifty B at equilibrium constant one, so Q equals one.
Add ten A to lower Q below K, then predict net conversion toward B before equilibrating.
Equilibrate to fifty-five of each and check that the total stays one hundred ten rather than reverting to its original value.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
For a one-to-one fixed-volume A ⇌ B reaction, Q = B/A and equilibrium requires Q = K. Adding material changes total mass; equilibration then conserves A + B and sets B/A to the selected K.
Where this idea is useful
A practical use
Predict the direction of adjustment by comparing Q with K instead of memorising that every disturbance is simply cancelled.
A common misconception
“Equilibrium restores every original concentration.”
The system reaches a composition satisfying the equilibrium condition under the new constraint; added material changes the conserved total.
What this explanation leaves out
- Only a one-to-one fixed-volume reaction endpoint is calculated. There are no reaction kinetics, pressure changes or activity corrections.
Why is there no reaction-time animation?
The endpoint is calculated algebraically without rate constants. An invented speed would add an unsupported kinetic claim.
Which quantity is conserved after your disturbance, and which ratio must settle?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.