How does pKa change with temperature?

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Answer 1 · 2015-08-09T14:46:13

In general, #"p"K_"a"# decreases as temperature increases.

#K_"a"# measures the position of equilibrium for the dissociation of an acid.

#"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_"a"# increases!

Since #"p"K_"a" = -logK_"a"#, an increase in #K_"a"# means a decrease in #"p"K_"a"#.

For example, if #K_"a"# increases from #10^-6# to #10^-5#, #"p"K_"a"# decreases from #6# to #5#.