I'm still not getting it ! help !!

Question

The Delta G for freezing of H2O(l) at -10 degrees C is -210 J/mol and the heat of fusion of ice at this temperature is 5610 J/mol.

Find the entropy change of the universe when 3 mol of water freezes at -10 degrees C.

Thank you !!

Answer 1

DG = DH - TDS

DS = (DG - DH) / -T

Gibbs free energy is negative for the spontaneous freezing of water at -10C, and DH is negative, since heat is released as water freezes.  That's why the air that comes from behind your refrigerator is hot.

DS = (-210 J/mol - (-5610 J/mol) / -264K

DS =  -20.5 J/molK

As you would expect, the entropy decreases as we go from liquid to solid.

For three moles, the entropy change would be -61.5 kJ/K