Question

Find the change in entropy (in kJ K-1) for the condensation of 2.3 g of water (H2O; 18.0 g mol-1) at 100 Celcius, if the enthalpy of vaporization of water is 40.65 kJ mol-1.

Answer 1

Mass of Water = 2.3g

Molar Mass of Water = 18g/mol

Moles of Water = (Mass of Water / Molar Mass of water)

  

= 0.123mol

Enthalpy of Vaporization = 40.65kJ/mol

For 0.123mol, enthalpy of vaporization will be 0.123mol x 40.65kJ/mol = 5kJ

Temperatue = 100 Celcius = (100+273)K = 373K

Change in Entropy = (5kJ/373K) = 0.0134kJ/K