Question

One kg of an ideal gas (gas constant R=287 J/kg·K) undergoes an irreversible process from state-1 (1 bar, 300 K) to state-2 (2 bar, 300 K). The change in specific entropy (s₂−s₁) of the gas (in J/kg·K) in the process is __________.

Accepted Answer

The correct answer is -198.9 J/kg·K (± 3). Since T is unchanged, only the pressure term of the entropy-change formula contributes: Δs = Cp ln(T2/T1) − R ln(p2/p1) = 0 − 287×ln(2) ≈ −287×0.6931 ≈ −198.9 J/kg·K. (Entropy, a state property, depends only on end states, not on whether the process is reversible.)

Explanation