Chemistry · Equilibrium

Le Chatelier's Principle Explorer

The gas mixture in the cylinder is at equilibrium: N₂O₄(g) ⇌ 2 NO₂(g), with ΔH° = +57.2 kJ per mole of reaction (endothermic as written). N₂O₄ is colorless and NO₂ is brown, so the color of the gas shows where the equilibrium sits.

Disturb the equilibrium by changing the temperature, squeezing or expanding the volume, or adding and removing gas. Compare the reaction quotient Q to the equilibrium constant K to predict which way the mixture shifts, then check the numbers and the color. Record data points to build your own table.

Model notes

K here is Kc in mol/L. It is set to 0.0058 at 298 K and moved to other temperatures with the van't Hoff equation, which assumes ΔH° is constant between 250 K and 400 K. That is a good approximation over this range, and real values drift slightly.
Each dot stands for a fixed amount of gas, shown under the cylinder. Particles do not collide with each other in the picture. The counts, not the motion, carry the chemistry.
Every disturbance is solved exactly: the page finds the amount of N₂O₄ that reacts so that Q equals K again. Adding a catalyst is not offered because a catalyst changes how fast equilibrium is reached, not where it sits.
Treat the numbers as a model. For classroom use, check the trends against a textbook table of Kc or Kp values.

Sources

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