Project ForgeThermodynamics
Entropy & Second Law
GATE 2019
Medium
Air of mass 1 kg, initially at 300 K and 10 bar, is allowed to expand isothermally till it reaches a pressure of 1 bar. Assuming air as an ideal gas with gas constant of 0.287 kJ/kg·K, the change in entropy of air (in kJ/kg·K, round off to two decimal places) is
0.66 kJ/kg·K(± 0.02 accepted)
Explanation
For an isothermal process of an ideal gas, Δs = −R ln(p2/p1) = 0.287 × ln(10/1) = 0.287 × 2.3026 ≈ 0.66 kJ/kg·K.
Source: GATE ME 2019 Session 1 (Set 1) (2019)
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