Kw calcuation

[Daniel Yu 1E]

Why is the activity of water equal to 1 when you are calculating the Kw with [H3O+][OH-]/[H2O]^2?

[Benjamin Feng 1B]

Water is the solvent for the equation, and there is a huge excess of it compared to the OH- and H+ ions. This means that even if we did include it, the concentration barely changes.

[Joseph Saba]

I would suggest to just look at it in terms of concentration, activity seems like an advanced topic for gen chem.

[Hannah Romeo 1J]

The Kw equation follows the previous logic of setting up K expressions. Pure solids and liquids are not included in the expression as they are in such excess that there equilibrium concentration is negligible. This results in Kw = [H3O+][OH-] as the molar concentration of hydronium and hydroxide are the only concentrations that change significantly in the reaction.

[Mariah]

Its basically omitted because it only changes slightly.

[AniP_2D]

Since water is a liquid, it is omitted from the equilibrium constant, giving the denominator in this specific equilibrium constant a value of 1.