Intermediate Topic 351 of 1102 Thermodynamics & Energetics
Enthalpy of Solution
Heat change when one mole of solute dissolves in solvent.
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In-depth explanation of Enthalpy of Solution
The enthalpy of solution is the heat change when one mole of a solute dissolves in a given amount of solvent at constant pressure. It can be viewed as the sum of two opposing contributions: the lattice enthalpy, the energy needed to separate a solid into gaseous ions and which is endothermic, and the hydration enthalpy, the energy released when water molecules surround the ions and which is exothermic. Whether the overall process releases or absorbs heat depends on which contribution dominates. A negative value means the solution warms, while a positive value means it cools, as seen in cold packs. This quantity is usually measured experimentally with a coffee-cup calorimeter.
Going deeper: Enthalpy of Solution
Key ideas: Think of dissolution as lattice breaking, which costs energy, followed by hydration, which releases energy. The net sign determines whether the solution warms or cools. Both depend on ion charge and size: small, highly charged ions have strong lattices and strong hydration.
Common mistakes and connections: Do not assume that every salt dissolving cools the solution, since many such as calcium chloride warm it. Also, a positive enthalpy of solution does not prevent dissolving, because entropy can drive it. This topic connects to solubility, to lattice enthalpy and to the Gibbs energy of dissolution.
Visualization of Enthalpy of Solution
Enthalpy of solution of salts: negative values warm the solution (NaOH, CaCl2), positive values cool it, as in instant cold packs using NH4NO3. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Dissolving sodium hydroxide releases heat strongly, with a molar enthalpy of solution of about -44 kJ, while dissolving ammonium nitrate absorbs heat.
Frequently asked questions about Enthalpy of Solution
What is Enthalpy of Solution?
Heat change when one mole of solute dissolves in solvent.
Is Enthalpy of Solution a beginner, intermediate or advanced topic?
Enthalpy of Solution is a intermediate topic in Thermodynamics & Energetics. It builds on the vocabulary of beginner topics in this area.
What should I learn before Enthalpy of Solution?
Study these earlier topics in Thermodynamics & Energetics first: Standard State, Enthalpy of Combustion, Enthalpy of Neutralization.
What comes after Enthalpy of Solution?
The next topics in Thermodynamics & Energetics are Hess's Law and Reaction Enthalpy from Formation Data.
Can I practise Enthalpy of Solution with quizzes?
Yes. The interactive lesson includes a self-check question on Enthalpy of Solution, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Enthalpy of Solution fits in Thermodynamics & Energetics
Enthalpy of Solution is topic 23 of 91 in Thermodynamics & Energetics.