Equilibrium Shift
Let a reversible gas reaction settle into equilibrium, then disturb it — add a reactant, remove product, compress or expand the vessel, or heat or cool it — and watch the concentrations shift and resettle into a new equilibrium, with a visible colour change for the nitrogen dioxide reaction.
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What you can adjust
- Reaction
- 0 – 1
- Temperature
- 260 – 340 K
- Initial [reactant A]
- 0 – 1 mol/L
- Initial [reactant B]
- 0 – 1 mol/L
- Initial [product]
- 0 – 1 mol/L
- Disturbance
- 0 – 7
- Disturbance time
- 1 – 8 s
Which reversible gas-phase reaction to run.
Starting temperature. 298 K (~25 degC) is the reference temperature the equilibrium constant is quoted at.
Starting concentration of the first reactant (NO2, or N2 for the Haber reaction).
Starting concentration of the second reactant. Only used by the N2 + 3 H2 <=> 2 NH3 reaction (H2) — ignored for 2 NO2 <=> N2O4, which has only one reactant.
Starting concentration of the product (N2O4, or NH3 for the Haber reaction).
What disturbs the equilibrium partway through the run. 'Add inert gas' is the case everyone gets wrong — at constant volume it changes nothing, because it changes no reacting species' concentration.
When (in seconds) the disturbance is applied. The reaction is given this long to reach its initial equilibrium first.
About this simulation
What it shows
A sealed gas reaction settles into equilibrium, is disturbed partway through, and then settles again. The concentrations are traced over time, and the nitrogen dioxide mixture changes colour as its concentration changes.
The key idea
A reversible reaction reaches a balance where the forward and backward rates match. If you disturb it, it shifts to partly undo the change (Le Chatelier's principle) and finds a new balance with the same equilibrium constant, unless the temperature changed.
Try this
With 2 NO₂ ⇌ N₂O₄, set Disturbance to Compress (halve volume): the brown deepens at the squeeze, then eases as the mixture shifts to N₂O₄, which has fewer gas molecules.
Adding an inert gas at constant volume changes nothing, because it does not change the concentration of any reacting gas.