In the equilibrium expression for the reaction
H2O(l)+CO32−(aq)⇌HCO3−(aq)+OH−(aq),
water does not appear explicitly. Which of the following best explains this omission?
a) Including water would change the units of K, so chemists leave it out to keep K unitless.
b) Water is the solvent, so all solvent species are automatically left out of equilibrium expressions.
c) The concentration of pure liquid water is effectively constant and is built into the equilibrium constant.
d) By convention, the molar concentration of water is fixed at 1M, so it cancels from the expression.