Solution Found!
(a) Why is the heat of fusion (?Hfus) of a substance
Chapter 11, Problem 4P(choose chapter or problem)
Problem 4P
(a) Why is the heat of fusion (ΔHfus) of a substance smaller than its heat of vaporization (ΔHvap)?
(b) Why is the heat of sublimation (ΔHsubl) of a substance greater than its ΔHvap?
(c) At a given temperature and pressure, how does the magnitude of the heat of vaporization of a substance compare with that of its heat of condensation?
Questions & Answers
QUESTION:
Problem 4P
(a) Why is the heat of fusion (ΔHfus) of a substance smaller than its heat of vaporization (ΔHvap)?
(b) Why is the heat of sublimation (ΔHsubl) of a substance greater than its ΔHvap?
(c) At a given temperature and pressure, how does the magnitude of the heat of vaporization of a substance compare with that of its heat of condensation?
ANSWER:
Solution 4P
Step 1
(a) Here we have to explain why is the heat of fusion (ΔHfus) of a substance smaller than its heat of vaporization (ΔHvap).
The amount of heat release when a solid substance is converted into liquid is called as heat of fusion, it is denoted as ΔHfus. Similarly the heat of vaporization refers to the change between liquid and gas states, it is denoted as ΔHvap. In the change from solid to liquid, the kinetic energy of the molecules must increase partially to break the intermolecular attractions between molecules. In the change from liquid to gas, the kinetic energy of the molecules must increase to overcome the intermolecular forces.
As the amount of energy required to overcome the intermolecular forces for the molecules to move freely in the gaseous state is much greater than the amount of energy needed to allow the molecules to move more easily among each other.
Thus the heat of of vaporization (ΔHvap) of a substance is greater than heat of fusion (ΔHfus).