Liquids and Solids

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Elias Omar 1G
Posts: 52
Joined: Fri Sep 28, 2018 12:17 am

Liquids and Solids

Postby Elias Omar 1G » Sun Mar 17, 2019 12:05 am

I still don't understand: Why do liquids and solids (pure substances) not affect the value of K or Q?

MariahClark 2F
Posts: 60
Joined: Wed Nov 15, 2017 3:04 am

Re: Liquids and Solids

Postby MariahClark 2F » Sun Mar 17, 2019 12:18 am

p\Pure liquids and pure solids have activities that are one (they don't appear in the mass action expression). Thus if you add more of them they will not affect the equilibrium at all. Solubility is a situation like this. If you have a saturated solution and you add more solid nothing happens (the reaction does not shift to the right even though you have added more reactant). You need to change the concentrations or pressures in the mass action expression to affect the equilibrium.

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Re: Liquids and Solids

Postby Chem_Mod » Sun Mar 17, 2019 12:19 am

For K and Q, you are typically using the concentrations or partial pressures of the chemical species to write those expressions. But it's very difficult to define or even measure the concentrations or partial pressures of pure solids and pure liquids. It's much clearer how to measure the concentrations or partial pressures of gases and aqueous solutions. :)

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