Le Chatelier's principle was described to me as:

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

I do not understand the phrase, "...the position of the equilibrium moves to counteract the change."

How can the equilibrium "move?" I know that the equilibrium constant cannot change so that cannot be it.


Let's keep this simple. Think about adding vinegar (acetic acid) to water.

$$\ce{CH3COOH + H2O <=> H3O^+ + CH3COO^-}$$

The equilibrium equation is

$$\ce{K_a} = \dfrac{\ce{[H^+][CH3COO^-]}}{\ce{[CH3COOH]}}$$

Le Chatelier's principle simply says that if I add more acetic acid to the water then the solution gets more acidic. However if I add more water, then the solution gets less acidic. Hence the equilibrium moves.(In this case it works to a point. Adding a drop of water to glacial acetic acid isn't an aqueous solution...)

  • 2
    $\begingroup$ It "moves", huh? ;-) $\endgroup$ Jul 24 '18 at 8:22
  • $\begingroup$ I think it is better depicted by $K_\mathrm{a}$ (acid dissociation constant) instead of $K_\mathrm{\alpha}$, isn't it? $\endgroup$ Jul 24 '18 at 11:27
  • $\begingroup$ @GaurangTandon - Thanks for pointing out blooper... $\endgroup$
    – MaxW
    Jul 24 '18 at 13:08

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