Question

Question #53869

Answer 1

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`