Lattice Enthalpies

LATTICE ENTHALPIES
- What is enthalpy change ∆H?
The amount of heat evolved or absorbed in a reaction at constant pressure
- What are the standard conditions?
T – 298 K / 25 degrees
P – 1 bar
C – 1 mol dm-3
- What is the standard enthalpy change of formation ∆𝐇𝒇 ⦵?
The enthalpy change for a reaction between elements in their standard
states (at standard temperature and pressure)

Standard enthalpy change of atomisation


Ionisation enthalpy


Electron affinity


Bond dissociation enthalpy




- What is the lattice enthalpy?
The enthalpy change for the conversion of 1 mole of a solid into 1 mole of
the constituent gaseous ions
- Is lattice enthalpy endothermic or exothermic?
Strongly endothermic due to strong electrostatic interactions between the
ions in the solid
Negative lattice enthalpy is strongly exothermic
- What is Hess’ Law?
The overall enthalpy change for a reaction is equal to the sum of the
enthalpy changes for all the individual steps
Drawing a Hess’ Law Cycle
With bond dissociation energy (BDE) – we HALVE the given value