Question

What is latent heat of vaporization?
A.Heat absorbed when a substance changes phase from solid to gas
B.Heat absorbed when a substance changes phase from liquid to gas
C.Heat released when a substance changes phase from liquid to gas
D.Heat absorbed when a substance changes phase from gas to liquid

Answer 1

Hint- We must remember that the first change of phase is melting, during which the temperature stays the same and water melts. The second change of phase is boiling, as the temperature stays the same during the formation of gas.

Step By Step Solution:
We know that the Latent heat is the energy that is absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its particular temperature. Also the latent heat associated with melting of solid or freezing of liquid is called the heat of fusion; that is associated with the vaporization of liquid or a solid or condensing a vapour which is known as the heat of vaporization. So, the answer is (B) Heat absorbed when a substance changes phase from liquid to gas.
Now, we know that the latent heat is normally expressed as the amount of heat (in units of calorie) per mole or unit mass of the substance which is undergoing a change of its natural state (phase). Latent heat arises from the works which are required to overcome the forces that hold atoms or molecules together in a material.

Note: we can understand that the regular structure of a crystalline solid is constantly maintained by force of attraction among its individual atoms. This is because of the latent heat forces. Hence latent heat forces oscillate little distant from their average positions in a crystal lattice.