Question

Why ionisation enthalpy is calculated for isolated gassous atom

Answer 1

Answer:

If isolated gaseous atom is in excited state comparatively lesser energy will be released of an electron. So, electron gain enthalpies of gaseous atom must be determined in their ground state. Lonization enthalpy is the energy required to remove an electron from an isolated gaseous atom in its ground state. In the gaseous phase, there is very little attraction between other particles which effects the ionisation energy.