Question

What is the effect of temperature on the ionic product of water? How will it change the pH value of a neutral solution?

Answer 1

The formation of hydrogen ions and hydroxide ions form water is an endothermic process.
$H_2{O}_{\left(l\right)}\rightleftharpoons H_{\left(aq\right)}^{+}+{OH}_{\left(aq\right)}^{-}$
The forward reaction absorbs heat. Thus according to Le Chatelier's principle increase in the temperature will shift the equilibrium to lower temperature. It means that the forward reaction will be favoured and more $H^{+}$ and ${OH}^{-}$ will be formed. Thus, the value of ionic product of water increases as temperature increases.
As $pH=-\log \left[H^{+}\right]$, thus with increase in temperature the pH of the neutral solution decreases.