Enthalpies

Definition of all the enthalpy changes required for Unit 5 AQA Chemistry

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Standard enthalpy of formation

Enthalpy change when one mole of compound is formed from it's constituent elements, all reactants and products in their standard states, under standard conditions

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Standard enthalpy of atomisation

Enthalpy change when one mole of gaseous atoms are formed from it's element in it's standard states under standard conditions. 

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Ionisation energies

First ionisation energy 

The standard enthalpy change when one mole of gaseous atoms are converted into one mole of ions, each with a single positive charge 

Second ionisation energy

The standard enthalpy change when one mole of gaseous ions loses one mole of electrons, to form a mole of gaseous ions, each with a two positive charges. 

And so on

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Lattice formation/dissociate enthalpy

Lattice formation enthalpy

The enthalpy change when one mole of solid ionic compound is formed from it's component gaseous ions.  

Lattice dissociation enthalpy

The enthalpy change when one mole of solid ionic compound is broken down into it's component gaseous ions. 

These two enthalpies have the same numerical value for a given compound - formation is negative (energy is given out) wherease dissociation is positive (energy must be put in) 

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Electron affinity

First electron affinity

The standard enthalpy change when one mole of gaseous atoms are converted to one mole of gaseous ions, each with a single negative charge

Second electron affinity

The enthalpy change when one mole of gaseous ions, each with a single negative charge, are converted to a mole of gaseous ions each with two negative charges

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Enthalpy of hydration and solution

Enthalpy of hydration

The standard enthalpy change when one mole of gaseous ions are completely surround by water molecules 

Enthalpy of solution

The standard enthalpy change when one mole of solute is dissolve in sufficient solvent to form a solution in which the molecules/ions are far enough apart not to interact with each other

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Mean bond enthalpy

The enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds 

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