The first ionisation potential of Na is 5.1 eV .The value of electron gain enthalpy (in eV) of Na+ will be :
-5.1
- 2.55
+ 2.55
-10. 2
As discussed in
Electron gain enthalpy -
When an electron is added to a neutral gaseous atom (x) to convert it into a negative ion, the enthalpy change accompanying the process is defined as the electron gain enthalpy
-
and,
Ionization enthalpy -
It is defined as the minimum amount of energy required to remove the outer most shell electron from an isolated gaseous atom (X) to form the gaseous ion.
- wherein
First IE is represented by:
and, Electron gain enthalpy is:
Since the equation is reversed, so: