To calculate the entropy change S when 2 moles of water vapor condense to liquid water at 100C and 1 atm pressure, we can use the formula:S = n * Hvap / Twhere n is the number of moles, Hvap is the enthalpy of vaporization, and T is the temperature in Kelvin.First, we need to convert the temperature from Celsius to Kelvin:T = 100C + 273.15 = 373.15 KThe enthalpy of vaporization for water is approximately 40.7 kJ/mol. Now, we can calculate the entropy change:S = 2 moles * 40.7 kJ/mol / 373.15 K To get the entropy change in J/molK, we need to convert kJ to J:S = 2 moles * 40,700 J/mol / 373.15 K S -218.96 J/molKThe entropy change when 2 moles of water vapor condense to liquid water at 100C and 1 atm pressure is approximately -218.96 J/molK.