How does pKa change with environment?

1 Answer
anor277
Jan 31, 2016

Good question. #pK_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:

#2H_2O rightleftharpoons H_3O^+ + HO^-#

At #298# #K# , #K_w# #=# #10^-14#; i.e #pK_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#, #pK_w# #<# #14#.

Does this make sense?

Related questions
See all questions in pH, pKa, Ka, pKb, Kb
Impact of this question
2830 views around the world
You can reuse this answer
Creative Commons License