`O(g) + 2e^(-) to O^(2-)(g) , DeltaH_(eg) = 744.7` kJ/mole . The positive value of `DeltaH_(eg)` is due to :

O(g) +2e^(-1) rarr O^(-2) (g) -E = +744.7 The reaction for the positive value of e is

Given that : O(g) + e^(-) to O^(-)(g) DeltaH = -142 kJ "mol"^(-1) O(g) + 2e^(-) to O^(2-)(g) Delta H = + 712 kJ "mol"^(-1) what will be the DeltaH for the reaction: O^(-)(g) + e^(-) to O^(2-)(g)

O + 2e^(-) to O^(-) , DeltaH = 639 kJ/mole O + e^(-) to O^(-) DeltaH o= -141 kJ/mole O^(-) + e^(-) to O^(-) , DeltaH = x kJ/mole What is the value of x ?

The formation of the oxide ion O^(2-)(g) , form oxygen atom requires first an exothermic and then an endothermic step as shown below, O(g)+e^(-) to O^(-)(g),DeltaH_(f)^(0)=-141kJ*mol^(-1) O^(-)(g)+e^(-) to O^(2-)(g),DeltaH_(f)^(0)=+780kJ*mol^(-1) ltbr. Thus, process of formations of O^(2-) in gas phase is unfavourable even through O^(2-) is isoelectronic with neon. it is due to the fact that-