Question

Which is more effective in cooling?
A.Ice at ${{\text{0}}^{\text{o}}}{\text{C}}$
B.Water at ${{\text{0}}^{\text{o}}}{\text{C}}$
C.Water at ${\text{10}}{{\text{0}}^{\text{0}}}{\text{C}}$
D.Ice at ${\text{10}}{{\text{0}}^{\text{0}}}{\text{C}}$

Answer 1

Hint:A pronounced cooling effect is caused by evaporation of water. The process in which a liquid changes into its gaseous state is called evaporation. If enough energy is given to the liquid in the form of heat , liquid can be converted into its vapor state. This heat energy which is used for such phase transformation is called heat of evaporation / latent heat of vaporization.

Complete answer:
Simply evaporation means vaporization from the surface of liquid below its boiling point. Now we can look at the factors which affect the rate of evaporation.
Factors affecting evaporation
Temperature: As temperature increases the rate of evaporation of liquid also increases, temperature and rate of evaporation of liquid are directly proportional to each other.
Surface area: Rate of evaporation of liquid increases with increase in surface area.
Humidity: Increase in humidity decreases the rate of evaporation of liquid , rate of evaporation of liquid inversely proportional to humidity.
Wind speed: Rate of evaporation of liquid is directly proportional to wind speed.
How does evaporation of liquid cause cooling?
 It is described as when surface of molecule absorbs energy(heat) it will increase kinetic energy of the molecules in the liquid and this increase in kinetic energy helps them to overcome the force of attraction between the liquid molecules , so that high energy molecule escape into vapor phase ,which lowers the average kinetic energy of remaining molecules , it will falls down the temperature of the system.
In the given question , for water and ice at ${\text{10}}{{\text{0}}^{\text{0}}}{\text{C}}$ there is no need for the system to absorb heat energy from the surrounding because already it has sufficient heat energy .
Whereas in the case of water and ice at ${{\text{0}}^{\text{0}}}{\text{C}}$ , Ice needs additional energy in order to convert itself to water. So that it absorbs more heat energy from surroundings making the system more cooler.

So, here the correct answer is option A

Note:
Latent heat of vaporization is defined as the physical property of a substance , which is the heat energy that is required to change one mole of liquid at its boiling point under atmospheric pressure. Evaporation occurs on the surface of liquid as liquid changes to gaseous phase.