3.1.5 the ionic product constant of water

chem whatarethemechanismsofchemicalchange

Reactivity 3.1.5 - the ion product constant of water, , shows an inverse relationship between and .

since most acid-base reactions involve ionisation in aqueous solution, water needs to be considered.

water self-ionises very slightly at normal temperatures and pressures

since the concentration of water can be considered to be constant due to the fact that so little of it ionises, it can be combined with to produce a modified equilibrium constant known as , the ionic product constant of water

has a fixed value at a specific temperature. at

in pure water, , so
at , giving

solutions can be defined as acidic, neutral, or basic according to their relative concentrations of ions

if the concentration of either or are known, the other can be calculated from the value of

is temperature dependent

as is an equilibrium constant, its value must be temperature dependent.

the reaction for the dissociation water is endothermic as it involves bond breaking, meaning that:

• increase in temperature shifts the equilibrium to the right, increasing the value of , increasing
• decrease in temperature shifts the equilibrium to the left, decreasing the value of , decreasing