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Chemistry Question on Thermodynamics

For the gas phase reaction, PCl5(g)<=>PCl3(g)+Cl2(g){PCl_{5} (g) <=> PCl_{3} (g) + Cl_{2} (g)} which of the following conditions are correct ?

A

ΔH=0 and ΔS<0{\Delta H = 0 \, and \, \Delta S < 0}

B

ΔH>0 and ΔS>0{\Delta H > 0 \, and \, \Delta S > 0 }

C

ΔH<0 and ΔS<0{\Delta H < 0 \, and \, \Delta S < 0}

D

ΔH>0 and ΔS<0{\Delta H > 0 \, and \, \Delta S < 0}

Answer

ΔH>0 and ΔS>0{\Delta H > 0 \, and \, \Delta S > 0 }

Explanation

Solution

The correct option is(B): ΔH>0 and ΔS>0{\Delta H > 0 \, and \, \Delta S > 0 }

For the reaction
PCl5(g)<=>PCl3(g)+Cl2(g){PCl_{5} (g) <=> PCl_{3} (g) + Cl_{2} (g)}
The reaction given is an example of decomposition reaction and we know that decomposition reactions are endothermic in nature, i.e, ΔH>0\Delta H > 0.
Further
Δn=(1+1)−1=+1\Delta 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){\Delta S > 0 (\Delta S \, is \, positive)}