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The enthalpy changes for these processes are given below: Cl₂(g) → 2Cl(g), 242.3 kJ mol⁻¹ I₂(g) → 2I(g), 151.0 kJ mol⁻¹ ICl(g) → I(g) + Cl(g), 211.3 kJ mol⁻¹ I₂(g) → I₂(g), 62.76 kJ mol⁻¹ If the standard states of iodine and chlorine are I₂(g) and Cl₂(g), respectively, the standard enthalpy of formation of ICl(g) is:

1. +16.8 kJ mol⁻¹
2. +244.8 kJ mol⁻¹
3. −14.6 kJ mol⁻¹
4. −16.8 kJ mol⁻¹

Correct answer: +16.8 kJ mol⁻¹

Solution

The standard enthalpy of formation for ICl(g) is calculated by combining the enthalpy changes of the dissociation of Cl₂ and I₂, and the formation of ICl from its elements. The positive value indicates that the formation of ICl from its standard states requires energy input, consistent with the calculated value of +16.8 kJ mol⁻¹.

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