# How does pKa change with temperature?

Aug 9, 2015

#### Answer:

In general, $\text{p"K_"a}$ decreases as temperature increases.

#### Explanation:

${K}_{\text{a}}$ measures the position of equilibrium for the dissociation of an acid.

${\text{HA" +"H"_2"O" ⇌ "H"_3"O"^+ + "A}}^{-}$

For most acids, the dissociation is an endothermic process.

According to Le Châtelier's Principle, if you add heat to an endothermic process, the position of equilibrium moves to the right.

${K}_{\text{a}}$ increases!

Since $\text{p"K_"a" = -logK_"a}$, an increase in ${K}_{\text{a}}$ means a decrease in $\text{p"K_"a}$.

For example, if ${K}_{\text{a}}$ increases from ${10}^{-} 6$ to ${10}^{-} 5$, $\text{p"K_"a}$ decreases from $6$ to $5$.