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For the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g), the reaction given is an example of decomposition reaction and we know that decomposition reactions are endothermic in nature, i.e., ΔH > 0. Further, n = (1 + 1) - 1 = 1. Hence more number of molecules are present in products which shows more randomness i.e., ΔS > 0 (ΔS is positive).

1. ΔS = ΔH/T
2. ΔS = ΔH/T × 273
3. ΔS = ΔH/T × 1
4. ΔS = ΔH/T × ΔS > 0

Correct answer: ΔS = ΔH/T

Solution

The correct relation for entropy change (ΔS) in terms of enthalpy change (ΔH) and temperature (T) is ΔS = ΔH/T. This is a standard thermodynamic equation.

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