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Energetics and Thermodynamics

Enthalpies of Solution and Hydration

  • 3 things to know
  • Papers 1 and 3

Overview

Enthalpy of solution and of hydration, and linking them through the lattice enthalpy.

What you need to know

Answer each one before you reveal it.

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Key term

What three enthalpy terms are related in the enthalpy cycle for dissolving an ionic compound?

Key term

What determines whether the enthalpy of solution is exothermic or endothermic?

Key term

How does ion size affect the magnitude of enthalpy of hydration?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the definition of enthalpy of solution?

    Model answer

    The enthalpy change when one mole of an ionic solid dissolves in sufficient water to form an infinitely dilute solution under standard conditions.

  2. 2

    What is the definition of enthalpy of hydration?

    Model answer

    The enthalpy change when one mole of gaseous ions is dissolved in sufficient water to form an infinitely dilute solution under standard conditions.

  3. 3

    What type of enthalpy change is the enthalpy of hydration — exothermic or endothermic?

    Model answer

    Exothermic.

  4. 4

    Why is enthalpy of hydration always exothermic?

    Model answer

    Because ion-dipole bonds form between the ions and water molecules, releasing energy.

  5. 5

    How can enthalpy of solution be calculated using a Hess's law cycle?

    Model answer

    By constructing a cycle linking lattice enthalpy, enthalpies of hydration of the ions, and enthalpy of solution.

  6. 6

    What three enthalpy terms are related in the enthalpy cycle for dissolving an ionic compound?

    Model answer

    Lattice enthalpy, enthalpies of hydration of the cation and anion, and enthalpy of solution.

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