Question

Why is second ionisation enthalpy higher than first?

Answer 1

Ionization enthalpy:

The amount of energy required to eject the last electrons from the outer most shell of an isolated gaseous atom is called Ionization energy.

The reason for the second ionization enthalpy is higher than the first:

We remove electrons from a neutral atom in the first ionization energy, but in the second ionization energy, we must remove electrons from a positive atom, where electrons are more securely bound due to increased attraction force, hence second ionization energy is higher than the first.