Question:
The electron gain enthalpy (Cl2,H) of chlorine is -3.7 eV mol-1. How much energy (in kcal mol-1) is released when 71 g of chlorine atoms are completely converted into Cl- ions in gaseous state? (1 eV = 23 kcal)
The electron gain enthalpy (Cl2,H) of chlorine is -3.7 eV mol-1. How much energy (in kcal mol-1) is released when 71 g of chlorine atoms are completely converted into Cl- ions in gaseous state? (1 eV = 23 kcal)
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Electron gain enthalpy is energy released per mole. Convert eV to kcal using the given conversion factor, and adjust for the number of moles if specified.
Updated On: July 22, 2025
- 1.072
- 10.72
- 17.02
- 85.1
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The Correct Option is D
Solution and Explanation
Electron gain enthalpy of Cl is -3.7 eV per atom.
For 1 mole of Cl atoms (35.5 g), energy released = $3.7 \times 23 = 85.1$ kcal mol$^{-1}$ (since 1 eV = 23 kcal).
Given mass = 71 g, which is $\frac{71}{35.5} = 2$ moles of Cl atoms.
Total energy for 2 moles = $2 \times 85.1 = 170.2$ kcal.
However, the question asks for energy per mole: 85.1 kcal mol$^{-1}$ matches option (4).
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