Enthalpy change and the electron affinity differ by a negative sign.
Electron affinity of an atom or molecule can be defined as the amount of energy that would be released when an electron is attached to a neutral atom or molecule in the gaseous state to form a negative ion.
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 (∆egH). Electron gain enthalpy provides a measure of the ease with which an atom adds an electron to form anion as represented by equation 3.3.
X(g) + e– → X–(g) (3.3)
The negative of the enthalpy change for the process depicted in equation 3.3 is defined as the ELECTRON AFFINITY (Ae ) of the atom
NCERT REFERENCE
Noble gases have large positive electron gain enthalpies because the electron has to enter the next higher principal quantum level leading to a very unstable electronic configuration.
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the negative of the enthalpy change for the process depicted in equation 3.3 is defined as the ELECTRON AFFINITY (Ae ) ___________________
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