Question

Place these hydrocarbons in order of decreasing boiling point.

paraffin, C40H82

ethane, C2H6

pentane, C5H12

2,2-dimethylpropane, C5H12

hexadecane, C16H34

Answer 1

All these are hydrocarbons

So, intermolecular force in them is London-Dispersion forces

The force is larger when molar mass of compound is larger

Larger force means larger boiling point

So, decreasing boiling point’s order will be same as decreasing molar mass

molar mass order is:

C40H82 > C16H34 > C5H12 > C2H6

There are 2 compound with formula C5H12. In this case, the one with greater branching will have less area of contact between molecules and hence lesser boiling point

So, order of decreasing boiling point is:

paraffin > hexadecane > pentane > 2,2-dimethylpropane > ethane