Irodov Problem 2.130

Entropy change depends on how temperature and volume (or pressure) shift together during heating. For an ideal gas, you'll use the fundamental entropy relation $dS = nC_V\frac{dT}{T} + nR\frac{dV}{V}$ (or its isobaric equivalent). The key is recognizing that in an isochoric process volume is locked, while in isobaric process pressure is locked—this determines which heat capacity and which logarithmic terms survive. Since $CO_2$ is polyatomic, you'll need its correct degrees of freedom to find $C_V$ and $C_P$.

Entropy change depends on how temperature and volume (or pressure) shift together during heating. For an ideal gas, you'll use the fundamental entropy relation $dS = nC_V\frac{dT}{T} + nR\frac{dV}{V}$ (or its isobaric equivalent). The key is recognizing that in an isochoric process volume is locked, while in isobaric process pressure is locked—this determines which heat capacity and which logarithmic terms survive. Since $CO_2$ is polyatomic, you'll need its correct degrees of freedom to find $C_V$ and $C_P$.