Question #53869

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Answer 1 · 2017-12-28T13:28:03

This requires a fairly good understanding of isothermal processes. I am assuming the solid/liquid is already at its phase change temperature.

When a system is undergoing a phase change, it's an isothermal process,

#DeltaS = (q_"rev")/T#, and

it's said that its entropy is generally constant until it's complete.

In more practical terms (since the above assumes this is a reversible process),

#DeltaS = (DeltaH)/T#

Hence, for melting that mass of ice, the entropy change would be positive since liquid will be more "disorganized" than the solid.

#(900g * ("mol")/(18g) * (5.99kJ)/("mol"))/(273K) * (10^3J)/(kJ) approx (1.10*10^3J)/K = DeltaS_1#

Likewise, the entropy change will be negative for the second change since the solid is more organized than the liquid phase.

#-DeltaS_1 approx (-1.10*10^3J)/K#