Lattice enthalpy: key terms
6 terms. Say the definition out loud, tap to check, then say whether you knew it. Back to the topic
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Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic lattice from its gaseous ions under standard conditions.
Examiners say Formation of the lattice from gaseous ions, so it is exothermic. "One mole of gaseous ions" is the common wrong answer.
Enthalpy change of atomisation
The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
Examiners say For chlorine it is ½Cl₂(g) → Cl(g): one mole of atoms, half a mole of molecules.
First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Examiners say Gaseous atoms and gaseous ions: include the state symbols in the equation.
First electron affinity
The enthalpy change when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1– ions.
Examiners say The first is exothermic; the second is endothermic because the electron is repelled by the negative ion.
Enthalpy change of solution
The enthalpy change when one mole of a solute dissolves completely in a solvent.
Examiners say ΔH(solution) = –lattice enthalpy + sum of the hydration enthalpies of the ions.
Enthalpy change of hydration
The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions.
Examiners say More exothermic for smaller ions and for ions of higher charge, which attract water molecules more strongly.
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