Topic 15: Energetics/thermochemistry - 15.1 Energy cycles

Nature of science: Making quantitative measurements with replicates to ensure reliability-energy cycles allow for the calculation of values that cannot be determined directly. (3.2)


Essential idea: The concept of the energy change in a single step reaction being equivalent to the summation of smaller steps can be applied to changes involving ionic compounds

Representative equations (eg M+(g) -> M+(aq)) can be used for enthalpy/energy of hydration, ionization, atomization, electron affinity, lattice, covalent bond and solution.

Enthalpy of solution, hydration enthalpy and lattice enthalpy are related in an energy cycle.

Applications and skills

Construction of Born-Haber cycles for group 1 and 2 oxides and chlorides.

Construction of energy cycles from hydration, lattice and solution enthalpy. For example dissolution of solid NaOH or NH4Cl in water.

Calculation of enthalpy changes from Born-Haber or dissolution energy cycles.

Relate size and charge of ions to lattice and hydration enthalpies.

Perform lab experiments which could include single replacement reactions in aqueous solutions.


Polarizing effect of some ions producing covalent character in some largely ionic substances will not be assessed.

The following enthalpy/energy terms should be covered: ionization, atomization, electron affinity, lattice, covalent bond, hydration and solution.

Value for lattice enthalpies (section 18), enthalpies of aqueous solutions (section 19) and enthalpies of hydration (section 20) are given in the data booklet.