Question

The boiling point of water, ethyl alcohol and diethyl ether are ${\text{10}}{{\text{0}}^{\text{o}}}{\text{C}}$, ${\text{78}}{\text{.}}{{\text{5}}^{\text{o}}}{\text{C}}$ and ${\text{34}}{\text{.}}{{\text{6}}^{\text{o}}}{\text{C}}$ respectively. The intermolecular forces will be in order of:
A. Water>ethyl alcohol>diethyl ether
B. Ethyl alcohol>water>diethyl ether
C. Diethyl>ethyl alcohol>water
D. Diethyl ether>water>ethyl alcohol

Answer 1

We know that Intermolecular forces are electrostatic in nature and comprises van der Waals forces and hydrogen bonds. The three main types of intermolecular interactions are,
-Dipole-dipole interactions
-London dispersion forces
-Hydrogen bonds

Complete step by step answer:
We must remember that molecules present in liquids combine to other molecules by means of intermolecular interactions that are weaker than the intramolecular interactions, which bind the atoms together inside molecules and polyatomic ions.
Van der Waals forces:
We can say van der Waals forces' is a common term that is used to describe the attraction of intermolecular forces between molecules. There are two types of van der Waals forces: weak London Dispersion Forces and stronger dipole-dipole forces.
Hydrogen Bonding:
A chemical bond in which one molecule containing hydrogen atom is attracted to an electronegative atom especially nitrogen, oxygen, or fluorine atom, generally of another molecule is defined as hydrogen bonding.
The increase in boiling point usually happens with respect to the molar mass. The molar mass rises with the size of the electron cloud, the strengths of intermolecular attractions increases with increasing molar mass. Higher the molar mass, size of the electron cloud would be more, higher polarizability would be seen and the strength of the intermolecular forces would be stronger and the increase in boiling point occurs.
The intermolecular attraction present in water is hydrogen bonding.
The intermolecular attractions present in ethyl alcohol are hydrogen bonding and van der Waals force (London dispersion force).
The intermolecular attractions present in diethyl ether van der Waals force (London dispersion force).
We know that hydrogen bonding is the strongest intermolecular force of attraction when compared to other intermolecular attractions. So, we can say the water could have the strongest intermolecular forces. Ethyl alcohol could have the second strongest intermolecular force and the least intermolecular force is diethyl ether. Therefore, the order of intermolecular forces is Water>ethyl alcohol>diethyl ether.
So, the correct answer is “Option A”.

Note:
We have to remember that the enthalpy of vaporization of liquid depends on its boiling point. The boiling point of ethylene is said to be greater because of its increase in molar mass. Stronger the intermolecular force of attraction, higher the boiling point, greater would be the enthalpy of vaporization.
Example: Chlorine has London dispersion force and $ClF$ has their intermolecular forces as dipole-dipole attractions. The enthalpy of vaporization of liquid depends on its boiling point. The boiling point of chlorine is said to be greater. Stronger the intermolecular force of attraction, higher would be the boiling point, greater would be the enthalpy of vaporization. Therefore, the enthalpy of vaporization of chlorine would be greater than $ClF$.