Water standing in the open at $ {{32}^{o}}C $ evaporates because of the escape of some of the surface mole cuels. The heat of vaporisation (540 cal/g) is approximately equal to $ \varepsilon $ n, where $ \varepsilon $ is the average energy of the escaping molecules and n is the number of molecules per gram. The value of $ \varepsilon $ is close to
- $ 1.62\times 10^{-20}J $
- $ 4.23\times 10^{-20}J $
- $ 6.75\times 10^{-20}J $
- $ 8.31\times 10^{-20}J $
The Correct Option is C
Solution and Explanation
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Concepts Used:
Changes of State
A change of state is a physical change in a matter. They are reversible changes and do not involve any changes in the chemical makeup of the matter. Common changes of the state include melting, freezing, sublimation, deposition, condensation, and vaporization.
Read More: Properties of Matter
Changes Between Liquids and Solids:
How would you make ice cubes in a tray? First, you would fill the tray with water from a tap. Then you would place the tray in the freezer compartment of a refrigerator. The freezer is very cold. What happens next?
Freezing
Heat transfer occurs between the warmer tray and the colder air in the freezer. The warm water loses heat to the cold air in the freezer. This heat transfer occurs until no energy is available for the particles to slide past each other. This forces them to remain in fixed positions, locked in place by the force of attraction between them. This way liquid water is changed into solid ice.
Melting
If you took out the ice cubes from the freezer and placed them in a warm room, the ice would absorb energy from the warmer air around them. This absorbed energy would facilitate them to overcome the force of attraction holding them together, enabling them to slip out of the fixed position that they held as ice. The process in which a solids change to a liquid is called melting.