Why Ignore Liquid or Solid Volume When Calculating K

[gconcha]

Why is it that when calculating for the K_P (aka the Equilibrium Constant via pressures), that we don't take into account the volume taken up by liquid or solids in the container with the gas? Since they're hard to compress, wouldn't that reduce the amount of volume available for the gases?

[Rita Chen 1B]

I think one thing is that the activity of a solid or liquid is equal to 1, so it doesn’t affect the K constant. Also in terms of solids, it is not dissolved, so would not have a concentration and I think something similar can be said with liquids as well.

[Vicki Liu 2L]

Kp is calculated using partial pressures not volume. Liquids and solids are excluded from the expression because they are available in excess so their pressures do not change before and after equilibrium.

[Jack Riley 4f]

Liquids and solids cannot be dissolved or have their pressures changed in solution so they are not factored in when calculating K.

[BNgo_2L]

Liquids and Solids don't have/have minimal changes in pressures nor concentrations, so they are typically not involved in computing the equilibrium constant.

[Jamie Lee 1F]

Liquids and solids don't necessarily dissolve in solvent, which is a main component of "concentration", which is then the focus of equilibrium calculations.

[Bilal Pandit 1J]

K is all about the concentrations, and the change in the liquid and solid-state is negligible so we can just ignore that.

[RichBollini4G]

Liquids and Solids don't have/have minimal changes in pressures nor concentrations, so they are typically not involved in computing the equilibrium constant.

very helpful, thank you