GATE 2018 ME (ME1) – Question 33
An ideal gas changes from 300 K, 100 kPa to 600 K, 500 kPa. Specific heats cp = 1 and cv = 0.7 kJ/kg K. Specific entropy change, to two decimals, is ______ kJ/kg K.
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Correct answer: 0.20 to 0.22
Explanation
Gas constant is $R=c_p-c_v=0.3$ kJ/kg K. Entropy change is $\Delta s=c_p\ln(T_2/T_1)-R\ln(p_2/p_1)=\ln2-0.3\ln5=0.210316$, rounded to 0.21 kJ/kg K.