1. Write the $K_w$ expression and the autoionization of water equation: $$K_w = [H_3O^+][OH^-]$$ $$2H_2O \leftrightharpoons H_3O^+ + OH^-$$ 2. If the $K_w$ increases with increasing temperature, the products concentration is increasing ($H_3O^+$ and $OH^-$). 3. If adding something increases the concentration of products, that "thing" is on the reactants side: $$2H_2O + heat \leftrightharpoons H_3O^+ + OH^-$$ Therefore, the reaction is endothermic.
Work Step by Step
Use the knowledge and concepts that we have learned in the last chapters, following the step-by-step above.