Gibbs Free Energy of Dissolution

Determine the direction of dissolution. A negative result favors dissolution, a positive result favors the solid state. Warming a cooling tower can flip the sign and drive calcium out as scale.

$$\Delta G=\Delta H-T\Delta S$$

Variables

Symbol	Meaning	Unit
$\Delta G$	Gibbs free energy change (sign gives the verdict)	kJ/mol
$\Delta H$	Enthalpy change, the balance of lattice disruption cost against hydration payoff	kJ/mol
T	Absolute temperature, weights the entropy term	K
$\Delta S$	Entropy change, the system preference for dispersion and mixing	kJ/(mol K)

Worked example

If delta G is negative, dissolution is favored. If delta G is positive, the solid state is favored.

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Part of The Blueprint of Water