GATE 2021 CY – Question 29

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. · 1 mark · Numerical answer

A reversible heat engine absorbs 20 kJ of heat from a source at 500 K and dissipates it to the reservoir at 400 K. The efficiency of the heat engine is _______%.

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Correct answer: 20 to 20

Explanation

A reversible engine between two reservoirs has Carnot efficiency η=1−Tc/Th. Substituting gives 1−400/500=0.20, or **20%**. Of the 20 kJ absorbed, 4 kJ becomes work and 16 kJ is rejected; the heat amount cancels when calculating efficiency.