Whether a salt dissolves depends on enthalpy of solution and the entropy increase.
Practise Thermodynamics & Energetics All Thermodynamics & Energetics topics
Whether a solid dissolves depends on the Gibbs energy of dissolution, delta G equals delta H minus T delta S, where delta H is the enthalpy of solution and delta S is the entropy change of the system. Dissolution is spontaneous only if delta G is negative, which requires a large enough entropy increase to offset any positive enthalpy. When a crystalline solid dissolves, its ions gain positional freedom and disperse, usually increasing entropy, although the water molecules ordered around the ions reduce it. The balance of these effects determines solubility. Thermodynamic analysis therefore explains why some salts dissolve readily while others remain largely insoluble.
Key ideas: Evaluate delta G sol from delta H sol minus T delta S sol. Entropy gain from dispersing ions competes with the entropy loss from ordering water around small, highly charged ions, which is why some salts have negative entropy of solution. Solubility product connects through delta G degree equals minus RT ln Ksp.
Common mistakes and connections: Do not assume that solids always become more soluble with temperature: it depends on the sign of delta H sol. Gases usually dissolve exothermically and become less soluble when heated. The topic joins enthalpy of solution to solubility equilibria.
Dissolution is governed by delta G = delta H - T delta S; solubility curves show how temperature shifts the balance for different salts. The interactive lesson shows this as a live animation or chart.
Sodium chloride dissolves spontaneously even though its enthalpy of solution is slightly positive, because the entropy gain from dispersing the ions outweighs that small positive enthalpy term.
Whether a salt dissolves depends on enthalpy of solution and the entropy increase.
Thermodynamics of Dissolution is a intermediate topic in Thermodynamics & Energetics. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Thermodynamics & Energetics first: Calorie vs Joule, Heat of Fusion of Ice, Heat of Vaporization of Water.
The next topics in Thermodynamics & Energetics are Gibbs-Helmholtz Equation and Van't Hoff Equation.
Yes. The interactive lesson includes a self-check question on Thermodynamics of Dissolution, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Thermodynamics of Dissolution is topic 87 of 91 in Thermodynamics & Energetics.