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For the gas phase reaction, PCl5(g) ⇌ PCl3(g) + Cl2(g), which of the following conditions are correct?

1. ΔH = 0 and ΔS < 0
2. ΔH > 0 and ΔS > 0
3. ΔH < 0 and ΔS < 0
4. ΔH > 0 and ΔS < 0

Correct answer: ΔH > 0 and ΔS > 0

Solution

The reaction involves the dissociation of PCl5 into PCl3 and Cl2, which increases the number of gas molecules. This indicates an increase in entropy (ΔS > 0). Additionally, bond breaking is endothermic, so ΔH > 0.

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