23.2.3—Calculations: the energy cycles in 23.2.2

Write the known enthalpy values on a labelled cycle, choose a sign convention, then use Hess’s law to isolate the unknown. Include every ion with its stoichiometric coefficient.

Check units and direction after rearrangement. A quick magnitude check should match the expected strength of ion–water or lattice attraction.

If ΔHsol, lattice dissociation and one hydration term are known, the missing hydration term is the residual after subtracting the other route contributions.

Do not average the hydration values or change a sign because the numerical answer is negative; the arrow direction determines the sign.