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Enthalpy of Solution Cycle Calculator

Hess's Law applied to dissolution: lattice enthalpy and hydration enthalpies.

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ΔH Solution

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Overview

The Enthalpy of Solution Cycle is a thermodynamic framework based on Hess's Law used to calculate the energy change when an ionic solid dissolves in water. It breaks the process into two theoretical steps: the endothermic separation of the ionic lattice into gaseous ions and the exothermic hydration of those ions by water molecules.

Symbols

Variables

= Lattice Enthalpy, ^+ = Hyd. Enthalpy (cation), ^- = Hyd. Enthalpy (anion), = ΔH Solution

Lattice Enthalpy
kJ/mol
Hyd. Enthalpy (cation)
kJ/mol
Hyd. Enthalpy (anion)
kJ/mol
ΔH Solution
kJ/mol

Apply it well

When To Use

When to use: Apply this equation when determining the solubility of an ionic compound or calculating missing enthalpy values in a Born-Haber style cycle. It assumes the solution is formed at standard temperature and pressure and results in infinite dilution.

Why it matters: This relationship explains why some substances dissolve endothermically, cooling their surroundings, while others release significant heat. It is vital in chemical engineering for designing heat exchange systems and in pharmacology for predicting drug solubility.

Avoid these traps

Common Mistakes

  • Using formation lattice enthalpy (negative) instead of dissociation (positive).
  • Convert units and scales before substituting, especially when the inputs mix kJ/mol.
  • Interpret the answer with its unit and context; a percentage, rate, ratio, and physical quantity do not mean the same thing.

One free problem

Practice Problem

Calculate the enthalpy of solution (ΔHsol) for Sodium Chloride (NaCl) given that the lattice dissociation enthalpy is +788 kJ/mol, the hydration enthalpy of Na⁺ is -406 kJ/mol, and the hydration enthalpy of Cl⁻ is -363 kJ/mol.

Lattice Enthalpy788 kJ/mol
Hyd. Enthalpy (cation)-406 kJ/mol
Hyd. Enthalpy (anion)-363 kJ/mol

Solve for: dHsol

Hint: Sum the lattice dissociation enthalpy and the two hydration enthalpies according to the formula.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Atkins' Physical Chemistry
  2. IUPAC Gold Book: Enthalpy of solution
  3. Wikipedia: Enthalpy of solution
  4. IUPAC Gold Book
  5. Atkins' Physical Chemistry, 11th ed.
  6. McQuarrie, Donald A. Physical Chemistry: A Molecular Approach.
  7. Atkins' Physical Chemistry (11th ed.) by Peter Atkins, Julio de Paula, and James Keeler
  8. Chemistry (5th ed.) by Peter Atkins and Loretta Jones