A hypothetical non-metal has a first electron gain enthalpy () of and a second electron gain enthalp — Periodic Table and Periodicity Chemistry Question
Question
A hypothetical non-metal $X$ has a first electron gain enthalpy ($\Delta_{eg}H_1$) of $-200 \text{ kJ/mol}$ and a second electron gain enthalpy ($\Delta_{eg}H_2$) of $+500 \text{ kJ/mol}$. What is the total enthalpy change (in $\text{kJ}$) required to convert $2.0 \text{ moles}$ of isolated gaseous $X$ atoms into $X^{2-}$ gaseous ions?
Answer: 600
💡 Solution & Explanation
The energy required to convert one mole of $X$ to $X^{2-}$ is the sum of the successive electron gain enthalpies: $\Delta H_{\text{total}} = \Delta_{eg}H_1 + \Delta_{eg}H_2 = -200 + 500 = +300 \text{ kJ/mol}$. For exactly 2 moles of atoms, the total energy change is $2 \times 300 = 600 \text{ kJ}$.
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