The first electron gain enthalpy () of an Oxygen atom is and its second electron gain enthalpy () is . What is the net overall enthalpy change (in ) for the full double-reduction process ?

Question

The first electron gain enthalpy ($\Delta_{eg}H_1$) of an Oxygen atom is $-141 	ext{ kJ/mol}$ and its second electron gain enthalpy ($\Delta_{eg}H_2$) is $+744 	ext{ kJ/mol}$. What is the net overall enthalpy change (in $	ext{kJ/mol}$) for the full double-reduction process $O_{(g)} + 2e^- ightarrow O^{2-}_{(g)}$?

Prashant Kotian · Accepted Answer

Correct answer: 603. By Hess's Law, the total enthalpy change for a multi-step process is the algebraic sum of the individual step enthalpies. Thus, the net enthalpy change for the addition of two electrons is .

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