Question

The latent heat of vaporization of a substance if always:
A) greater than its latent heat of fusion.
B) greater than its latent heat of sublimation.
C) Equal to its latent heat of sublimation
D) less than its latent heat of fusion.

Answer 1

Hint- The latent heat of vaporization is the heat required to change 1 mole of liquid to vapor at its boiling point under standard atmospheric pressure.

Complete step by step answer:
We know that a substance can be changed from solid to liquid and liquid to gas and vice-versa. Now, as we change solid into a gas, we need to increase its kinetic energy, moving them further until the force of attraction becomes less allowing them to flow easily. But the forces of attraction still exist in liquid only their strength is reduced.
Now, as we change liquid into gas, the kinetic energy is increased to that point, where the force of attraction does not exist. That is forces of attraction completely become zero, allowing molecules to freely move.
Now when we compare these two cases, changing solid into liquid (the latent heat of fusion) and liquid into a gas (the latent heat of vaporization), the energy required to increase the kinetic energy so that molecules can flow easily is much less than the energy required to increase the kinetic energy to make the molecules move freely that is, no force of interaction. In other words, the energy required to completely separate the molecules of the substance is more than the energy required to reduce the separation between the molecules.
Hence, “greater than its latent heat of fusion” is correct. That is the correct option is (A).

Note:
*The latent heat of fusion is the heat is the energy that needs to be removed from the liquid to freeze it.
*The latent heat of vaporization is the energy required to vaporize a liquid.
*The latent heat of sublimation is the energy required to convert solid into a gas.