To calculate the change in entropy of the gas as it expands irreversibly, we need to know the initial and final volumes of the gas. However, we don't have enough information to determine the volumes directly. Instead, we can use the fact that the process is irreversible and the external pressure is constant to find the change in entropy.For an irreversible expansion against a constant external pressure, the change in entropy S can be calculated using the formula:S = n * R * ln Vf / Vi where n is the number of moles of gas, R is the gas constant 8.314 J/molK , Vf is the final volume, and Vi is the initial volume.Since we don't have the volumes or the number of moles, we can use the ideal gas law to relate the initial and final volumes to the initial and final pressures:PV = nRTRearranging the equation to solve for the volume, we get:V = nRT / PSince the initial pressure is 2 atm and the final pressure is 1 atm, the final volume Vf will be twice the initial volume Vi :Vf = 2 * ViNow we can substitute this relationship into the entropy change formula:S = n * R * ln 2 * Vi / Vi S = n * R * ln 2 We still don't have the number of moles n , but since it's a constant, the change in entropy will be proportional to the number of moles. So, we can calculate the change in entropy per mole of gas:S_per_mole = R * ln 2 S_per_mole = 8.314 J/molK * ln 2 S_per_mole 5.76 J/molKSo, the change in entropy of the gas as it expands irreversibly against a constant external pressure of 1 atm is approximately 5.76 J/molK per mole of gas.