Le Chatelier's Principle interactive widget showing how equilibrium systems respond to disturbances
Nothing at equilibrium ever stops reacting
At equilibrium the forward and reverse reactions are both still running, just at the same speed. Here two A particles join to make one P (2A ⇌ P), and the forward reaction releases heat. Change the amount of A, squeeze the box or heat it, and watch where the mix ends up.
Equilibrium Response
No stress applied
Change the amount of A, or press a button. Watch the mix settle.
System at equilibrium
Reactant A concentration
No AOriginalDouble A
Products formed
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A remaining
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In this picture, 2A ⇌ P turns two gas particles into one, so squeezing the box (Pressure ×2) shifts it toward P. When you increase pressure on a gaseous equilibrium, the system shifts toward the side with fewer gas moles — because that partially relieves the pressure you just applied. For example, in the Haber process (N₂ + 3H₂ ⇌ 2NH₃), the left has 4 gas moles and the right has 2. Increasing pressure shifts right, making more ammonia. But the pressure never drops back to its original value — the shift only partially opposes your change. This is why industrial ammonia synthesis runs at 200 atmospheres: the equilibrium favours products under high pressure, even though the system fights back by making some.
Know This
Only temperature changes K itself — pressure and concentration changes shift the position but leave the equilibrium constant unchanged.