# How does pKa change with environment?

Jan 31, 2016

Good question. $p {K}_{a}$'s should DECREASE with INCREASING temperature. I will confine my discussion to the water molecule, but the argument should be generalizable.

#### Explanation:

Now autoprotolysis of water is a well-known (and well documented) reaction:

$2 {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + H {O}^{-}$

At $298$ $K$ , ${K}_{w}$ $=$ ${10}^{-} 14$; i.e $p {K}_{w}$ $=$ $14$.

Because the reaction AS GIVEN is BOND-BREAKING (i.e we have to break a strong $O - H$ bond), at higher temperatures, the equilibrium should lie farther to the right. So at $T$ $>$ $298$ $K$, $p {K}_{w}$ $<$ $14$.

Does this make sense?