Question

Which one of the following lists the alkane in order of decreasing boiling point?

• A. Octane, Methane, Butane, Ethane
• B. Methane, Ethane, Propane, Butane
• C. Hexane, Octane, Propane, Methane
• D. Hexane, Pentane, Propane, Ethane

Answer 1

The correct option is D Hexane, Pentane, Propane, Ethane

As the number of carbon atoms in alkanes increases the number of different isomers increases dramatically. To give an indication of the variation in boiling points of different isomers of the same alkane, cycloalkanes have boiling points typically around ${10}^{0}C$ to ${20}^{0}C$ higher than the corresponding linear alkane. Boiling points of alkanes increase with an increase in the number of n. A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the greater surface area in contact, thus the greater van der Waals forces, between adjacent molecules. Thus Hexane>Pentane>propane>ethane.