The standard enthalpy change for the phase transition reaction of solid carbon dioxide dry ice to gaseous carbon dioxide at 298 K and 1 atm pressure can be determined using the given standard enthalpy of sublimation.The phase transition reaction is represented by the following equation:CO2 s CO2 g The standard enthalpy of sublimation Hsub is the enthalpy change when one mole of a substance changes from solid to gas at a constant temperature and pressure. In this case, the standard enthalpy of sublimation for solid carbon dioxide is given as 25.2 kJ/mol.Since the phase transition reaction involves the direct conversion of solid carbon dioxide to gaseous carbon dioxide, the standard enthalpy change for this reaction H is equal to the standard enthalpy of sublimation:H = HsubTherefore, the standard enthalpy change for the phase transition reaction of solid carbon dioxide to gaseous carbon dioxide at 298 K and 1 atm pressure is 25.2 kJ/mol.