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GATE 2021 CY – Question 64

Physical Chemistry · Equilibrium: Laws of thermodynamics. Standard states. Thermochemistry. Thermodynamic functions and their relationships: Gibbs-Helmholtz and Maxwell relations, Gibbs-Duhem equation, Van’t Hoff equation. Criteria of spontaneity and equilibrium. Absolute entropy. Partial molar quantities. Thermodynamics of mixing. Chemical potential. Fugacity, Activity and Activity coefficient. Chemical equilibria. Dependence of equilibrium constant on temperature and pressure. · 2 marks · Numerical answer

A 2 L gas at 1 atm is heated reversibly to a final volume of 3.5 L. The absolute work done on the gas is ______ J (nearest integer).

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Correct answer: 151 to 153

Explanation

Using the intended constant external pressure, the work on the gas is w=−PΔV=−1 atm×(3.5−2) L=−1.5 L atm. Convert using 1 L atm=101.325 J: w=−151.99 J. Its absolute value is therefore **152 J**. Reversibility alone would not fix the work without a specified pressure path.