Understanding the Second Law of Thermodynamics...?

Question

When we place objects of different temperatures in a room, they usually come to the same temperature. But a damp object, even if it starts at room temperature, becomes cooler than the room. How does this play into the second law of thermodynamics?

Answer 1

It becomes cooler at first because of evaporative cooling. Evaporation is an endothermic reaction. But sooner or later, after all the moisture is gone, it will achieve equilibrium and assume room temperature.

What does the 2nd law have to do with any of this? Well endothermic reactions are only possible if the entropy of increased disorder of the reaction (liquid molecules turning to gas) overwhelms the entropy lost by making the surrounding material cooler. So above a certain temperature, the fluid (water) will evaporate and cool the object for a while.

That explanation of the 2nd Law's impact is a bit of a stretch, but the bottom line is that the 2nd Law dictates which way ANY natural process runs over time.

Answer 2

To tie it in directly with the scond law. Say our state is the room, the rag, the air, and the water on the rag. If we were to just pick a state at random, there are a lot more possible states where the air is evaporated in the room, than there are having all the water concentrated in the rag, or in one corner, etc. Thus there are many more microstates possible when the water is evaporated. Thus entropy drives it in this direction.

Answer 3

I agree with the previous answers, but they should point out that the damp cloth is cooler at first, but if you leave it in the room for longer than the initial period of evaporation, the cloth will eventually reach the room temperature.

Answer 4

It is due to the water evaporating from the object that makes it cooler.

Read more here...
http://en.wikipedia.org/wiki/Evaporative_cooling

Answer 5

evaporation causes heat loss. You question has little to do with the second law.