Question

When sweat evaporates from your skin the temperature of your skin decreases. This is because

a. energy is being applied to the skin.
b. the sweat is trapping molecules with a higher speed.
c. the water molecules with a higher speed are escaping .
d. the water molecules with a slower speed are escaping.

Answer 1

Well A is somewhat right, but energy is leaving the skin, and B is wrong because if the sweat was trapping the molecules with a higher speed your skin would not cool down, and C is wrong because the higher speed molecules is your water weight, but it is not on you to cool you down, so D is the right answer because the slower molecules are not leaving really, the molecules are on the skin too cool you down.

Answer 2

C - The water molecules with a higher speed are escaping

The temperature of a substance is a measure of the average kinetic energy of the molecules. Therefore as the higher speed molecules escape (by evaporation - that is the breaking of the bonds between the molecule and the rest of the liquid), the average KE of the skin decreases and hence the temperature decreases.