Question

What effect does branching of an alkane chain have on its boiling point?

Answer 1

Hint: It is imperative to know that an alkane compound experiences Van der waal force which is an example of a weak force. There is a clear correlation between these forces and the boiling point which the students need to know about to solve this conceptual problem.

Complete Step by Step Solution:
Well, such questions involve a correlated interrelationship which essentially helps in solving this conceptual question.
When the branching on an alkane compound increases, the surface area of the entire compound or the molecule decreases.
The intermolecular forces such as the Van der waal forces tend to decrease with such branching because the surface area of the molecule decreases. We should already know that the Vander waal force is directly proportional to the surface area of the molecule.
So, in a nutshell the Van der waal force decreases with the increase in branching in the alkane molecule.
Now, as the Vander waal forces which are intermolecular forces decrease, there is a relative ease in terms of boiling the compound. Hence the boiling point of the molecule decreases with increase in branching, because the lowered Van der Waal forces are overcome at a lower temperature point (when boiled/heated).

Note: Now, in the hindsight we could also consider the melting point. So, again the relationship remains the same here. With more branching, there is a decrease in the surface area of the molecule which in turn leads to reduction in the intensity of the Van der waal force and then this will result in the decrease of the melting point too, similar to the boiling point.