Equilibrium shift explorer

Chemical equilibrium is dynamic: disturb it and the system shifts to partially undo the change. This simulation uses the classic color-changing N2O4/NO2 system so you can literally see equilibrium shift. Learning goals: predict shift direction with Le Chatelier's principle for temperature, pressure, and concentration changes; explain why only temperature changes K; use Q versus K to justify the direction of shift.

At equilibrium, forward and reverse rates are equal.

Controls

Temperature slider: Heats or cools the mixture; the forward reaction is endothermic.
Pressure control: Changes the container volume, shifting toward fewer or more gas moles.
Add reactant / product: Injects extra N2O4 or NO2 into the closed container.
Q vs K readout: Shows live values of Q and K and the current shift direction.

The chemistry

\text{N}_2\text{O}_4(g) \rightleftharpoons 2\,\text{NO}_2(g)

Dinitrogen tetroxide dissociation equilibrium

Q_c = \frac{[\text{NO}_2]^2}{[\text{N}_2\text{O}_4]}

Reaction quotient for the system

Q < K \Rightarrow \text{shifts right};\quad Q > K \Rightarrow \text{shifts left}

Shift direction rule

Assumptions

The container is closed, so no matter enters or leaves except when you add it.
Only temperature changes the equilibrium constant K.
The color intensity is proportional to NO2 concentration.

Guided activity

Raise the temperature and watch the brown color deepen or fade.
Compress the mixture and observe which direction the system shifts.
Add extra reactant and watch the system consume it.
Compare the reaction quotient Q with K at each step to confirm the shift direction.

Challenge questions

Predict the color change before heating, using Le Chatelier's principle.
Explain why a catalyst would not change the final color.
Find the conditions that give the deepest brown color and justify them.