A Level Chemistry, Unit 5 AQA, Thermodynamics Definitions

Revisions Notes

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  • Created by: Charly
  • Created on: 07-05-12 17:35

Enthalpy Change of Formation

The enthalpy change when one mole of a compound is formed from it's elements in their standard states, under standard conditions.

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Enthalpy Change of Atomisation in an Element

The enthalpy change when 1 mol of gaseous atoms is formed from an element in it's standard state, under standard conditions.

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The Bond Dissociation Enthalpy

The enthalpy change when all the bonds of the same type in 1 mol of gaseous molecules are broken, under standard conditions.

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The First Ionisation Enthalpy

The enthalpy change when 1 mol of gaseous 1+ ions is formed from one mole of gaseous atoms, under standard conditions.

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First Electron Affinity

The enthalpy change when 1 mol of gaseous 1- ions is formed from 1 mol of gaseous atoms, under standard conditions. 

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The Enthalpy of Solution

The enthalpy change when 1 mol of solute is dissolved in sufficient solvent that no further enthalpy change occurs on further dilution, under standard conditions.

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The Enthalpy Change of Hydration

The enthalpy change when 1 mol of aqueous ions is formed from 1 mol of gaseous ions, under standard conditions.

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Lattice Formation Enthalpy

The enthalpy change when 1 mol of a solid ionic compound is formed from its gaseous ions, under standard conditions.

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Lattice Dissociation Enthalpy

The enthalpy change when 1 mol of a solid ionic compound is completely dissociated into its gaseous ions, under standard conditions.

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Hess's Law

The enthalpy change is independent of the route taken.

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Why are Theoretical lattice enthalpies different f

The purely ionic model assumes that all ions are spherical and that their charge is evenly distributed.

Although experimental data that we gather from Born-Haber cycles is usually different, this gives evidence that ionic compounds usually have some covalent character.

Due to this covalent character, the positive and negative ions aren't exactly spherical. 

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