Home Chemistry Thermodynamics and Thermochemistry Heat of Reaction The boiling point of a substance X at 1 atm …
Chemistry Thermodynamics and Thermochemistry Heat of Reaction Single Correct MCQ
Published on: August 14, 2026

The boiling point of a substance X at 1 atm pressure is 500 K. The enthalpy of vapourisation at the boiling point of X( λ ) is 80 kJ/mol. The molar specific heat of X ( λ ) = 5 × 10 –3 kJ/mol and C P of X(g) = 5 × 10 –4 kJ/mol.What is the molar latent heat of vapourisation of X( λ ) at 800 K and at 1 atm ?

A
Lesser than 80 kJ
B
Greater than 80 kJ
C
Equal to 80 kJ
D
Since 800 K is the higher temperature than the boiling point of X( λ ) ; therefore, enthalpy of vapourisation is not applicable

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Text Solution

Verified by Experts
The correct answer is:
A

Δ H 1 = 5 × 10 –3 × (500 – 800) × 10 –3 kJ;

Δ H 2 = 80 kJ;

Δ H 3 = 5 × 10 –4 × (800 – 500) × 10 –3 kJ

Δ H 1 = – 0.0015 kJ ; Δ H 2 = 80 kJ,

Δ H 3 = 0.00015 kJ ;

Δ H = Δ H 1 + Δ H 2 + Δ H 3 ;

Hence

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