A rigid and insulated tank of volume of \(2 \mathrm{~m}^{3}\) is divided into two equal compartments by a partition. One compartment contains an ideal gas at \(400 \mathrm{~K}\) and \(3 \mathrm{MPa}\), while the second compartment contains the same gas at \(600 \mathrm{~K}\) and \(1 \mathrm{MPa}\). This partition is punctured and the gases are allowed to mix. Determine the entropy change of the gas. The isobaric molar heat capacity of the gas is equal to \((5 / 2) R\).