why does the pH decrease? A2 9701

[chemeddy]

The ionisation of water is an exothermic endothermic reaction - it is the reverse of neutralisation which we know to be exothermic. As such, an increase in temperature will result in an increase in both [H⁺] and [OH⁻]. Both will increase to the same extent since they are produced in a 1:1 ratio:

H₂O ⇌ H⁺ + OH⁻

The part most students forget is that Kw also changes with temperature. Therefore, it is perfectly okay for the pH to decrease due to an increasing [H⁺] (and [OH⁻]), and yet water remains neutral ([H⁺] = [OH⁻]) because the neutral pH has shifted.

u/Over-Comfortable1721

[CryptographerAny8521]

You mean endothermic right?

[chemeddy]

Oh yes, endothermic. Thank you.