For which solutes dissolved in a liquid is the overall enthalpy of solution exothermic?

Dissolving a solute is exothermic when forming solute–solvent attractions releases more energy than is needed to separate the particles. This happens for some solids, but not for most, since solid dissolution can be either exothermic or endothermic. Dissolving most gases in liquids releases heat, so the best choice is “some solids and most gases.”

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