Le Châtelier's Principle: The Piston Chamber
Explore why adding inert gas shifts equilibrium under constant pressure but not constant volume.
About this simulation
- What
- An interactive Chemistry simulation of Le Châtelier's Principle: The Piston Chamber.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-01-07
Key Concepts
Partial Pressure
The pressure contribution of each gas in a mixture. Partial pressure = (mole fraction) × (total pressure).
Le Châtelier's Principle
When a system at equilibrium is disturbed, it shifts to counteract the change.
Constant Volume vs Constant Pressure
Adding inert gas at constant volume doesn't change partial pressures; at constant pressure, volume expands.
Understanding Le Châtelier's Principle
Le Châtelier's Principle is a fundamental rule in chemistry stating that if a dynamic equilibrium is disturbed by changing the conditions, the system will shift its equilibrium position to counteract the applied change.
Key disturbance factors include changes in concentration, temperature, and total pressure. In gas-phase systems, shifts are dictated by the relative moles of gas on each side of the reaction and the resulting changes in partial pressures.
Through our piston chamber visualization, you can investigate the critical distinction between adding inert gas at constant volume (where no shift occurs) versus constant pressure (where a shift occurs toward the side with more moles of gas).
Equilibrium Shifts Summary
| Disturbance Factor | Change Applied | Equilibrium Shift Direction |
|---|---|---|
| Concentration | Increase Reactant / Decrease Product | Shift AWAY from added species |
| Decrease Reactant / Increase Product | Shift TOWARDS removed species | |
| Pressure (via Volume) | Increase Pressure (Decrease Volume) | Shift to FEWER moles of gas |
| Decrease Pressure (Increase Volume) | Shift to MORE moles of gas | |
| Temperature | Increase Temperature (Heat is added) | Shift Endothermic (+ΔH direction) |
| Decrease Temperature (Heat is removed) | Shift Exothermic (-ΔH direction) |
Frequently Asked Questions
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