To calculate the standard enthalpy change for the transition of liquid water at 100C to steam at the same temperature, we can use the given enthalpy of vaporization of water.Enthalpy of vaporization Hvap is the amount of energy required to convert 1 mole of a substance from the liquid phase to the gas phase at a constant temperature.In this case, the enthalpy of vaporization of water is given as 40.7 kJ mol.Since we are considering the transition of 1 mole of liquid water to steam at the same temperature 100C , the standard enthalpy change H for this process will be equal to the enthalpy of vaporization.H = HvapH = 40.7 kJ molTherefore, the standard enthalpy change for the transition of liquid water at 100C to steam at the same temperature is 40.7 kJ mol.