What is the molar entropy change for the freezing of water at 0degrees celsius? The enthalpy of fusion of water is 333.5J/g.

1 Answer
Truong-Son N.
May 1, 2018

For freezing at the normal freezing point, there is a phase equilibrium, so that #DeltaG_(fus) = 0#. Note that freezing is the opposite of what #DeltaH_(fus)# describes.

Therefore,

#cancel(DeltaG_(fus))^(0) = DeltaH_(fus) - TDeltaS_(fus)#

As a result,

#color(blue)(DeltaS_(f rz)) = -DeltaS_(fus) = -(DeltaH_(fus))/T#

#= (-"333.5 J/g")/("273.15 K") = color(blue)(-"1.22 J/g"cdot"K")#

Does this make physical sense? Freezing releases heat, so the entropy of the system decreases.

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