01Why things dissolve
Dissolving involves breaking solute–solute and solvent–solvent attractions (endothermic) and forming solute–solvent attractions (exothermic). Entropy usually increases.
Dissolution is favorable when ΔG = ΔH − TΔS < 0 — some endothermic dissolutions happen because of the entropy gain.
02Notebook box
ΔH_soln = break solute + break solvent + form interactions.
Worked example: NH₄NO₃ dissolves even though endothermic — the large +ΔS makes ΔG negative.