Answer to Question #78618 in Molecular Physics | Thermodynamics for Frank

Question

Explain why a hot humid day is far more uncomfortable than a hot dry day at the same temperature?

Answer 1

On a hot day man's body starts to pour sweat. The water in the sweat absorbs the heat released by man's body . The heat is used for vaporization of water. The water takes off the heat thus cooling the body. The water will evaporate quicker on a dry day, also more water will evaporate on dry day as dry air is not saturated with water vapor . The equilibrium of the process water(l) <-> water(vapor) will shift to the side of vapor formation. On a humid day the process of vaporization of water from the sweat goes slower as air is saturated with water vapor, the man' s body will be cooled slower. Moreover as air is saturated with water vapor the equilibrium water(l)<->water(vapor) will shift to the side of water(liquid) formation, i.e. more sweat will be formed. As water is condensed from the air the heat is released to man's body. So, on a humid day lots of sweat is formed that is hardly evaporated, there is almost no cooling of the body, moreover body receives additional heat from the process of water condensation.