Question

one mole of ice at 0 C is turned completely into steam by heating under 1 atm pressure. calculate the entropy change in the system with specific heat capacity and enthalpy/heat values.assuming they are all constant.

Answer 1

H2O(S) at 0oC to H2O(l) at 0oC     -------delta S1
H2O(l) at 0oC to H2O(l) at 100 oC ---------delta S2
H2O(l) at 100 oC to H2O(g) at 100 oC ---------delta S3

delta S1 = qrev/T = n*delta H fusion / T
                     =1*6.01/273.15
                     =0.022 KJ/K

delta S2 = nCp*ln(Tf/Ti)
            = 1* 0.07529*ln(373.15/273.15)
            = 0.0235 KJ/K

delta S3 = n*delta Hvap/T
            = 1*40.7 / 373.15
            =0.1091 KJ/K

So,
delta S= delta S1 + delta S2 + delta S3
         = 0.022 + 0.0235+ 0.1091
         = 0.1546 KJ/K
         = 154.6 J/K