Chemical Equilibrium Simulator (Le Chatelier)
Equations in this simulation
| ΔH° | enthalpy of reaction | negative: making ammonia gives out heat, so raising the temperature pushes the equilibrium back toward N₂ and H₂ | |
|---|---|---|---|
| n | moles of each gas | the molecules drawn are twenty per mole |
| p | partial pressure of each gas, bar | p = n R T ÷ V | |
|---|---|---|---|
| Q | reaction quotient: the same ratio for the mixture as it is now | below K the reaction runs forward, above K it runs backward, until Q = K | |
| K_p | equilibrium constant | set by the temperature alone, not by the amounts or the volume |
With the current values:
| ΔS° | entropy of reaction | −198 J/(mol·K): four molecules of gas become two | |
|---|---|---|---|
| ΔG° | standard Gibbs energy of reaction | negative below about 465 K, where ammonia is favored |
With the current values:
| p_total | total pressure | squeezing the vessel raises it, and the reaction answers by making fewer molecules: 4 become 2 |
|---|
With the current values:
How to use the chemical equilibrium simulator
- The vessel starts with one mole of nitrogen (blue pairs) and three of hydrogen (white pairs). They react to ammonia (one blue and three white) until the mixture reaches equilibrium, where ammonia forms as fast as it breaks down and Q equals K.
- Disturb it and watch it shift back, as Le Chatelier's principle says. Squeeze the vessel and the pressure rises, so the reaction makes more ammonia, turning four molecules into two. Heat it and, because making ammonia gives out heat, it shifts back toward nitrogen and hydrogen. Add a gas, or remove the ammonia, and the mixture moves to use it up or replace it.
- Turn off the catalyst and cool the vessel to see the other half of the story: at low temperature the equilibrium favors ammonia, but the reaction is so slow it hardly moves. The chart shows the equilibrium share of ammonia against temperature for the volume you chose.
Frequently asked questions
What is chemical equilibrium?
The state a reversible reaction settles into, where the forward and reverse reactions run at the same rate, so the amounts stop changing although molecules keep reacting both ways. For N₂ + 3H₂ ⇌ 2NH₃ it is reached when the reaction quotient Q = p(NH₃)² ÷ (p(N₂) p(H₂)³) equals the equilibrium constant K.
What is Le Chatelier's principle?
If an equilibrium is disturbed, it shifts in the direction that partly undoes the disturbance. Adding a reactant shifts it forward to use some up; removing a product shifts it forward to replace some; raising the pressure favors the side with fewer gas molecules; raising the temperature favors the direction that absorbs heat.
Why does the Haber process run hot if heat lowers the yield?
Because at a temperature where the yield is high the reaction is far too slow, even with a catalyst. Industry compromises: about 450 °C, an iron catalyst and 150 to 300 bar of pressure to win back yield, with the ammonia condensed out and the unreacted gas recycled. That last step is the Remove the NH₃ button.
Does a catalyst change the equilibrium?
No. It speeds up the forward and backward reactions by the same factor, so the mixture reaches equilibrium sooner but at exactly the same composition. Only the temperature changes K; pressure and amounts change Q, and the mixture then moves until Q equals K again.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.