Question

The vapour pressure of a substance is 21 torr at 300k. Calculate the vapour pressure at 310k if the enthalpy of vaporization is 24 kj/mol.

Answer 1

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Answer 2

Concept:

Clausius Clapeyron equation is an equation that relates the heat of vaporization and vapor pressure of a substance.

ln (P₁/P₂) = ΔH/R [ (1/T₂) - (1/T₁) ]

Where P₁ and P₂ are the vapor pressure of the substance at temperatures T₁ and T₂ respectively and ΔH is the enthalpy of vaporization.

Given:

The vapor pressure of a substance at 300 K is 21 Torr and the enthalpy of vaporization is 24 kJ/mol.

Find:

The vapor pressure of the substance at 310 K.

Solution:

Substituting the given values in the Clausius Clapeyron equation,

T₁ = 310 K, T₂ = 300 K, P₂ = 21 Torr, ΔH = 24 kJ/mol, R = 8.314 J/mol K

ln (P₁/P₂) = ΔH/R [ (1/T₂) - (1/T₁) ]

ln (P₁/ 21 ) = 24/8.314 [ (1/300) - (1/310) ]

ln (P₁/ 21 ) = 0.31039

P₁ = 28.643 Torr

Hence, the vapor pressure of the substance at 310 K is 28.643 Torr.

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