Question

Why is ice at $273K$ more effective in cooling than water at the same temperature?

Answer 1

Hint: For effective cooling, state of the matter is crucial. It is related to the latent heat of fusion of ice. Latent heat of fusion is defined for any solid that can change itself into liquid form. It is also called the enthalpy of fusion and is calculated only under constant pressure conditions.

Complete step by step answer:
> As we have observed in our homes, water can be a solid or liquid at $273\operatorname{K}$ or $0{}^\circ C$. The solid state of water has molecules tightly packed than the liquid state. That implies the kinetic energies of the molecules in liquid state are more than solid ones. So we can say, a solid at the same temperature is lower in energy than a liquid. In other words, to change the state of this particular solid into that of a liquid energy is needed.
> Now, what happens when ice changes into water? We can explain it as- when ice (solid form of water) absorbs heat from its surrounding, it gives the necessary energy to the molecules to overcome the forces that bind them together. This gradual process lets the ice slowly melt into water. During this process ice absorbs heat equalling in amount to its latent heat of fusion.
> As discussed in the hint, “Latent heat of fusion” is the energy that a solid absorbs to change into liquid or a liquid releases to change into solid, under constant pressure conditions. As our atmospheric pressure is $1\operatorname{atm}$we can take our whole earth to be in a constant pressure condition provided the places taken into consideration are at same height above the sea level.
> Now looking at ice and water we can surely say that ice is more effective in cooling than water at $273\operatorname{K}$ because it is in solid state while water is in liquid state. The amount of heat that ice will absorb from its surrounding is way more than that of water, hence bringing down the temperature of its surrounding. In the same way, steam is more effective than water at $373\operatorname{K}$ to heat things up.

Note: - The effectiveness of cooling can only be measured with precision under closed conditions where pressure is a constant.
The latent heat of fusion is only applied when the state of matter changes from solid to liquid or vice-versa. If the physical states involved are liquid and gas, then it becomes latent heat of vaporization.