# What does it mean for an equillibrium to move? [duplicate]

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.

• For starters, it should use the term "in response to" instead of "to counteract".
– A.K.
Jul 24 '18 at 3:22
• Also, I have an answer to a related question that may help provide clarity. chemistry.stackexchange.com/questions/75619/…
– A.K.
Jul 24 '18 at 3:25
• @A.K. I'm sorry but I don't understand how that answer helps with this question. It seems beyond anything I'm learning. Jul 24 '18 at 3:36
• Hi Leif Metcalf, welcome to Chem.SE! Your question seems to be possibly a duplicate of What does it mean to shift equilibrium?. Have a look at that question, and if it doesn't help, feel free to edit your question to offer more clarification, as to how your question is different from the one I linked. Thanks! Jul 24 '18 at 11:30
• Jul 24 '18 at 11:30

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...)

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