The table shows the enthalpy changes needed to calculate the lattice energy of potassium oxide, ${\mathrm{K}}_2\mathrm{O}$.

Type of enthalpy change	Value of enthalpy change/$\mathrm{kJ} {\mathrm{mol}}^{-1}$
first ionisation energy of potassium	$+418$
first electron affinity of oxygen	$-141$
second electron affinity of oxygen	$+798$
enthalpy change of formation of ${\mathrm{K}}_2\mathrm{O}$	$-361$
enthalpy change of atomisation of potassium	$+89$
enthalpy change of atomisation of oxygen	$+249$

Use the data in the table above to calculate the lattice energy of potassium oxide.

The table shows the enthalpy changes needed to calculate the lattice energy of potassium oxide, ${\mathrm{K}}_2\mathrm{O}$.

Explain why the second electron affinity of oxygen has a positive value. 

Define the term first ionisation energy.

Define the term enthalpy change of atomisation.

Draw and label a Born-Haber cycle to calculate the lattice energy of sodium chloride.

Explain why the lattice energy of sodium chloride has a value that is lower than the lattice energy of lithium chloride.

Draw an energy cycle to show the dissolving of magnesium iodide in water.

The table shows the values for all but one of the enthalpy changes relevant to this cycle.

Define enthalpy change of hydration.