## Chemistry: Atoms First (2nd Edition)

a. The autoionization of water is endothermic. b. $[H^+]$ and $[OH^-] = 2.34\times 10^{- 7}M$
a. According to the Le Chatelier principles, if the increase of temperature favors the products side of the reaction, this reaction is endothermic. - Let's imagine "heat" as a product/reactant: - If the increase of heat favors the right side of the reaction, it should be on the left side: $H_2O(l) + heat \lt -- \gt H^+(aq) + OH^-(aq)$ - If the "heat" is on the reactants side; the reaction is endothermic because it needs heat to occur. b. - Pure water solution : $[H^+] = [OH^-]$ - Create a unknown called 'x' that has the value of $[H^+]\ and\ [OH^-]$ - Write the $K_w$ expression, and calculate the x value: $[H^+] * [OH^-] = K_w = 5.47\times 10^{- 14}$ $x * x = 5.47\times 10^{- 14}$ $x^2 = 5.47\times 10^{- 14}$ $x = \sqrt { 5.47\times 10^{- 14}}$ $x = 2.34\times 10^{- 7}$ Therefore: $[H^+]\ and\ [OH^-] = 2.34\times 10^{- 7}M$