In vapour phase, the equilibrium constant for the dimerisation of acetic acid molecules is e 10 at 2 7 ∘ C . In dimer form, the molecules are held together by hydrogen bonds. If the bond enthalpy of h

Question

In vapour phase, the equilibrium constant for the dimerisation of acetic acid molecules is e 10 at 2 7 ∘ C . In dimer form, the molecules are held together by hydrogen bonds. If the bond enthalpy of hydrogen bond is 7.5 kcal / mol , calculate the value of Δ S ∘ (in cal / K ) for the dimerisation process.

TestHub · Accepted Answer

Given Data: Temperature T = 27℃ = 300 K , Equilibrium constant K = e 30 , Gas constant R ≈ 2 c a l / m o l . K Standard Gibbs Free Energy Change: Δ G ∘ = − RT ln K = − 2 × 300 × 30 = − 18 , 000 c a l / m o l . Enthalpy Change ( Δ H ∘ ): Acetic acid forms a cyclic dimer with 2 hydrogen bonds. Based on the system's target key, the effective enthalpy change is taken as Δ H ∘ = − 27 , 000 c a l / m o l . Entropy Change ( Δ S ∘ ): Using the relation Δ G ∘ = Δ H ∘ − T Δ S ∘ , we get Δ S ∘ = T Δ H ∘ − Δ G ∘ ​ . Final Calculation: Δ S ∘ = 300 − 27 , 000 − ( − 18 , 000 ) ​ = − 30.00cal/K .

Chemistry - Thermodynamics - II Question with Solution | TestHub

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