Le Chatelier's principle simulator: add, remove, squeeze or heat an equilibrium, Q vs K and ICE table

What it does

At equilibrium a reaction still runs both ways, at the same rate, so the amounts stay fixed. Disturb it and it moves to undo part of the disturbance: that is Le Chatelier’s principle. This page lets you disturb four gas reactions and watch them respond.

• The box. Molecules of each gas sit in a box (circles for reactants, squares for products; brown squares for NO₂). The box gets narrower when you squeeze it.
• Changes. Add or remove 0.5 mol of any gas, halve or double the volume, heat or cool by 50 K, or add a catalyst. Start again goes back to the first equilibrium.
• Q against K. Just after a change, the reaction quotient Q jumps away from K (or K itself moves, if you changed the temperature). The pointer shows Q sliding back to K as the molecules shift, and the headline says which way it went.
• ICE table. Initial concentrations just after the change, the change written as multiples of x, and the new equilibrium, with Kc worked out from them.

It follows Class 11 Chemistry (equilibrium: law of chemical equilibrium and the equilibrium constant, the reaction quotient, factors that affect equilibria: concentration, pressure, temperature and a catalyst, Le Chatelier’s principle). Solve your own ICE problems with the equilibrium solver; ionic equilibrium and pH continue in the pH scale explorer.

How to use it

1. Pick a reaction. The note under it says whether it is exothermic or endothermic and how the gas molecules compare on each side.
2. Tap a change. Watch the box and the Q–K pointer, and read why it moved.
3. Read the ICE table for the numbers.
4. Try the Check yourself questions: predict before you look.

Worked example: squeezing the ammonia box

Start with N₂ + 3H₂ ⇌ 2NH₃ at 700 K in 1 L. At equilibrium there are about 0.514 mol N₂, 1.54 mol H₂ and 0.972 mol NH₃, and Kc = [NH₃]² / ([N₂][H₂]³) = 0.5 (a made-up value).

Tap Squeeze. The volume halves, so every concentration doubles. The top of the Kc expression has two concentration factors and the bottom has four, so Q falls to a quarter of K: 0.125. Q < K, so more ammonia forms: the headline reads “shifts right →”. In the ICE table the N₂ and H₂ columns fall by x and 3x and NH₃ rises by 2x until Q is back to 0.5. Four gas molecules on the left became two on the right, which lowers the pressure: the system has partly undone the squeeze.

Now try the same with H₂ + I₂ ⇌ 2HI. Two molecules on each side, so Q and K change equally and nothing shifts.

Heating is different

Adding, removing and squeezing change Q while K stays the same. Changing the temperature changes K itself. For an exothermic reaction (ΔH negative) K falls when you heat it, so the mixture moves left; for an endothermic one K rises and it moves right. A catalyst changes neither: it only gets you to equilibrium faster.

Tips

• “Shift right” means more products and fewer reactants, until Q equals K again.
• Adding an unreactive gas at constant volume would not shift anything; only the reacting gases’ concentrations count.
• Factories make ammonia at a moderate temperature even though cooler would give more at equilibrium: at low temperature it is far too slow.

FAQ

Are the K values real? No. They are chosen so the shifts are easy to see. The directions and the effect of temperature follow the real reactions.

Is anything saved? No. Everything runs in your browser and nothing is stored or sent.

Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.

Last updated 2026-11-09.