Define ionisation enthalpy and electron affinity.

Explanation

Ionisation enthalpy is the energy required to remove an electron from an isolated gaseous atom in its ground state.
`X_((g))toX_((g))^(+)+e^(-)`
The ionisation ehthalpy is expressed in units kJ `mol^(-1).`
The enthalpy change accompanying the process of conversion of a neutral gaseous atom into negative ion by adding an electron is called gain enthalpy.
`X_((g))+e^(-)toX_((g))^(-)`
The electron gain enthalpy is also known as electron affinity of the atom under consideration.