How does water react to form ions?

1 Answer
anor277
Dec 29, 2015

Water undergoes autoprotolysis. The reaction is given in the next section.

Explanation:

H_2O rightleftharpoons H^(+) + HO^-.

Alternatively:

2H_2O rightleftharpoons H_3O^(+) + OH^-

Reaction (ii) is a bit more common these days. What we conceive to be the acidium ion, H^+ or H_3O^+, is actually a cluster of water atoms (4-5) with an extra proton, i.e. H_9O_4^+.

In any case the equilibrium is known for standard conditions (1 atm, 298K), and the ion product, K_w = [H_3O^+][HO^-] = 10^(-14).

Under non-standard conditions (i.e. > 298K), would you expect K_w to increase or decrease? Why?

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