# How does enthalpy affect solubility?

Sep 18, 2014

Decreasing the energy required to separate the solute particles and increasing the energy of solvation of the particles will increase the solubility if a substance.

The solution process involves three steps.

1. Separation of solvent particles; ΔH_1 >0.
2. Separation of solute particles, ΔH_2 >0.
3. Solvation of solute particles, ΔH_3 < 0.

ΔH_"soln" = ΔH_1 + ΔH_2 + ΔH_3

ΔH_1 and ΔH_2 are both positive. ΔH_3 < 0.

If |ΔH_3| > ΔH_2 + ΔH_2, then the solution process is favourable.

That is, solution will occur if the enthalpy of solvation is more negative than the sum of the enthalpies of separation.

This is important when ionic and polar substances are involved.

When nonpolar substances are involved, the enthalpy changes are small. In those cases, entropy changes become important factors.