$A-B\to A^{•}+B^{•};\Delta H=+xkJmo{l}^{-}$

$A-B\to A^{+}+B^{-};\Delta H=+ykJmo{l}^{-}$

The relationship between x and y in gaseous chase is

Generally heterolytic bond cleavage occur in case of bond between two highly different electronegative atoms. the bond formed between such atoms are stronger hence require more energy to break as compared to the bond formed between the atoms of same electronegativity.