Le Chatelier's PrincipleJEE Main

How equilibrium responds to stress — interactive Chemistry simulation for IIT-JEE.

Concept

Le Chatelier's principle: if a system at equilibrium is disturbed, it shifts to partly oppose the change. Adding a species, squeezing the volume, or heating each nudges the balance in a predictable direction — but only temperature actually changes the equilibrium constant $K_c$ .

Key formula

\text{pressure} \Rightarrow \text{toward fewer gas moles}; \quad \text{heat} \Rightarrow \text{toward the endothermic side}

Derivation

Adding reactant raises $Q$ below $K$ , so the forward reaction runs until $Q=K$ again. Compressing the gas favours the side with fewer moles to reduce pressure.

Heating supplies energy to the endothermic direction, so an exothermic forward reaction shifts backward and its $K_c$ falls. A catalyst changes neither position nor $K_c$ — it only reaches equilibrium faster.

Scenarios to explore

Le Chatelier's Principle — How equilibrium shifts under concentration, pressure & heat.

Real-world applications

Optimising industrial yields (Haber, Contact processes).
Controlling biochemical and blood-buffer equilibria.
Solubility and common-ion effects.

JEE exam tips

Only temperature changes $K_c$ ; everything else just shifts the position.
Adding an inert gas at constant volume does not shift the equilibrium.
Δn(gas) = 0 ⇒ pressure has no effect.

Common mistakes

Thinking a catalyst shifts the equilibrium (it does not).
Assuming pressure always favours products — it depends on Δn(gas).
Believing concentration changes alter $K_c$ (only temperature does).

Exam traps to avoid

Inert gas at constant pressure (volume rises) shifts toward more gas moles.
The shift only partially offsets the stress — it never fully cancels it.