Question

The boiling point of methane, ethane, propane and butane are given
Compound $C{H}_4\text{ C}{H}_3\text{C}{\text{H}}_3\text{ C}{H}_3\text{C}{\text{H}}_2\text{C}{\text{H}}_3\text{ C}{H}_3\text{C}{\text{H}}_2\text{C}{\text{H}}_2\text{C}{\text{H}}_3$
Boiling point/K $112\text{ 185 231 273}$
Which statement explains the increase in boiling point from methane to butane?
(A) Closer packing of molecules results in stronger Van der Waals forces.
(B) More covalent bonds are present and therefore more energy is required to break the bonds.
(C) More electrons in the molecules results in strong van der Waals forces
(D) More hydrogen bonds in the molecule results in strong hydrogen bonding.

Answer 1

Hint: Boiling point of any substance is defined as the temperature at which vapour pressure of a liquid equals the pressure surrounding and the liquid will convert to its vapour form. For example the boiling point of water is ${100}^{\circ }C$ .

Complete step by step solution:
First of all we will talk about the alkanes.
Alkanes: The compounds which are formed by carbon and hydrogen and have only a single bond between the carbon-carbon atoms, are known as alkanes. For example: The first member of the alkane family is ethane $(H_{3}C-C{H}_3)$ . The general formula of the alkane group is $C_n{H}_{(2n+2)}$ .

Number of carbon atom in alkane	Name of the parent chain
One	Methane
Two	Ethane
Three	Propane
Four	Butane
Five	Pentane
Six	Hexane
Seven	Heptane

Boiling point of any substance is defined as the temperature at which vapour pressure of a liquid equals the pressure surrounding and the liquid will convert to its vapour form. For example the boiling point of water is ${100}^{\circ }C$ .
Here we are given with the boiling points of methane, ethane, propane and butane.
Molecules which strongly interact with others through a variety of intermolecular forces and they cannot move easily. So the molecules which have stronger intermolecular bonds will have high boiling points. Here butane has higher intermolecular interactions between the atoms so it has high boiling point. So the molecule having more covalent bonds will require more energy to break the bonds.
Hence option B is correct.

Note:
Alkanes, alkenes and alkynes are bonded by covalent bonds. In this bond two atoms share their electrons with each other to complete their octets and attain stability. The higher the alkane higher will be the covalent bond and vice versa.