Are Both L and Aq Excluded From Equilibrium Constant Expressions?

[Michellekim1H]

So, I know that solids and liquids are not supposed to be included in Kc but I was wondering if Aq is excluded as well. Isn’t Aq liquid too? Also, I still don’t really understand why these things are excluded from the expression so can someone please explain to me why.

[Sebastian Lee 1L]

So, I know that solids and liquids are not supposed to be included in Kc but I was wondering if Aq is excluded as well. Isn’t Aq liquid too? Also, I still don’t really understand why these things are excluded from the expression so can someone please explain to me why.

Aq is included in the equilibrium constant expression. A molecule that is aqueous means that it is surrounded by water molecules (aka dissolved in water) but isn't actually a pure liquid. We never exclude aqueous solutions because these are very important since their concentration (moles per liter) changes in equilibrium reactions. It is only PURE liquids and solids that are excluded from the expression. This is because their concentrations don't really change as the reaction reaches equilibrium. Even though they're important in the reaction, their concentrations don't significantly change. For example, if you have something dissolving in a solvent, there will be so much excess solvent that doesn't react with the solute that the concentration is essentially unchanged. For solids, it just doesn't even make sense talking about moles per liter of a solid by itself.

[Miriam Villarreal 1J]

Pure solids and liquids are not included in the equilibrium constant expression. This is because they do not affect the reactant amount at equilibrium in the reaction, so they are disregarded. We can't increase the concentration of a pure liquid or pure solid and hence they are omitted from the expression

[Jainam Shah 4I]

Only pure solids and pure liquids are omitted from the equilibrium constant expression, because the concentration of a solid doesn't not make sense and for pure liquids the change in concentrations is very insignificant because it acts as a solvent.

[Jialun Chen 4F]

Aqueous solutions should be included in the equilibrium expression. Only solid (s) and liquid (q) are excluded.