Calculating Equilibrium Constant

[Emma Li 2C]

Why aren't solids included in calculating for the chemical equilibrium constant?

Thank you!

[Jingyi Li 2C]

You do not include the solids because you assume them to be pure. So, you do not really have a concentration for the solids (actually the number for it is just 1). Therefore, it is said to be not included in the equilibrium constant calculation.

[Chem_Mod]

Hi, Emma,
We don't include the solids in the equilibrium expression because their concentration stays constant. While the amount of solid may change as the reaction proceeds, the ration of the mol/volume will stay the same. The reason for it is the fact that only specific amount of solid can take up specific space, while for gases, for example, same amount of gas can take up the different amount of space (volume), thus changing the concentration.