Answer
The value of $K_w$ at $25^o C$ is $1.0 \times 10^{-14}$.
Work Step by Step
The equations for the autoionization of water and the expression for the ion product constant are in page 732, Section 16.5
The value of the constant at $25 ^{o}C$ is on the same section, in page 733.
$$H_2O(l) + H_2O(l) \leftrightharpoons H_3O^+(aq) + OH^-(aq)$$ or
$$H_2O(l) \leftrightharpoons H^+(aq) + OH^-(aq)$$
$$K_w = [H_3O^+][OH^-]$$ or
$$K_w = [H^+][OH^-]$$
The value of $K_w$ at $25^o C$ is $1.0 \times 10^{-14}$.
