5/15. Energetics/Thermochemistry

Standard enthalpy change of formation, ΔHf°  : the enthalpy change when 1 mole of a compound is formed under standard conditions from its elements in their standard states.

Lattice enthalpy, ΔHlat: the standard enthalpy change when 1 mole of gaseous ions is formed from the solid lattice under standard conditions.

Enthalpy change of hydration, ΔHhyd: the enthalpy change when 1 mole of gaseous ion is added to water to form a dilute solution. (ALWAYS NEGATIVE)

Enthalpy change of atomisation, ΔHatm: the standard enthalpy change when 1 mole of separate gaseous atoms are formed from the element in its standard state.

Enthalpy change of solution, ΔHsol : the enthalpy change when 1 mole of a substance is dissolved in a large excess of a pure solvent.

Ionisation energy, IE: the standard enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms or ions.

Electron affinity, EA: the standard enthalpy change when 1 mole of electrons are added to 1 mole of gaseous atoms or ions.

Electronegativity: measure of the tendency of an atom to attract a bonding pair of electrons.

The average bond enthalpy: Enthalpy change when I mole of a bond in a gaseous state is broken. It is an average calculated from a range of similar compounds.

e.g. HCl (g) --> H(g) + Cl(g) 

Exothermic reaction: a chemical reaction with an overall negative enthalpy change (heat is evolved)

Endothermic reaction: a chemical reaction with  an overall positive enthalpy change (heat is absorbed)

Activation energy (Ea): the minimum energy required for a chemical reaction to occur

Enthalpy level diagrams: (y-axis is not ΔH but just enthalpy, H)

Exothermic (-ve ΔH)                                        Endothermic (+ve ΔH)

           

Born-haber cycle: (ΔHlat = positive)