According to Hess's law, the total enthalpy of solution (∆H_soln) is the sum of the enthalpy changes of the individual steps involved in the formation of the solution:

1. Separation of solvent molecules (∆H₁)
2. Separation of solute molecules (∆H₂)
3. Mixing of the separated solute and solvent molecules to form the solution (∆H₃) Thus, ∆H_soln = ∆H₁ + ∆H₂ + ∆H₃. For an ideal solution, the total enthalpy of solution (or mixing) is zero (∆H_soln = 0), which implies ∆H₁ + ∆H₂ + ∆H₃ = 0.