NCERT Question 7 - Chapter 1 Class 9 - Matter In Our Surroundings

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

Answer

Ice at 273K (or 0° C) is solid while water at 273K (or 0° C) is a liquid. 

When both the substances, at 273K, are used for cooling, ice is more effective than water. 

This is because ice is a solid when it absorbs heat, it is used for two things

1. For changing its state from solid to water 
2. To increase its temperature from 0°C / 273K

Whereas on the other hand, water is a liquid, when it absorbs heat it is used 

1. To increase its temperature from 0°C / 273K

Thus, we can conclude that ice at 0°C / 273K consumes more heat than water at 0°C / 273K. 

Hence, ice at 273 K is more effective in cooling than water at the same temperature.

So, to summarise

Note :

Cooling effect is observed due to loss of heat to the surroundings.

The more heat is absorbed, the more cooling effect takes place