Entropy changes

Homework Statement

an ice cube is melted in water which is continuously stirred to be at a constant temperature of 0 degrees. the stirring is gentle enough so the work done is negligible.

my question is why in this case does the heat come from the air to melt the ice cube and not the water. why cant it be a bit of both or just the water.

also, for the total entropy change of the universe, wouldn't I just consider the S:ice + S:water = S:air?

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Andrew Mason
Homework Helper

Homework Statement

an ice cube is melted in water which is continuously stirred to be at a constant temperature of 0 degrees. the stirring is gentle enough so the work done is negligible.

my question is why in this case does the heat come from the air to melt the ice cube and not the water. why cant it be a bit of both or just the water.
Heat flow requires a temperature difference. Without heat flowing from the air to the water/ice, the water and the ice would reach and remain at the same temperature, 0C, and then there would be no further heat flow. So heat flow must occur from the surroundings to the water/ice.
also, for the total entropy change of the universe, wouldn't I just consider the S:ice + S:water = S:air?
The total entropy change is:

$$\Delta S_{universe} = \Delta S_{ice} + \Delta S_{water} + \Delta S_{air}$$

AM