Question

The boiling points of water, ethyl alcohol and diethyl ether are, ${{100}^{\circ }}C,{{78.5}^{\circ }}C, and {{34.6}^{\circ }}C$ respectively. The intermolecular forces will be in the order of:
A. water > ethyl alcohol > diethyl ether
B. ethyl alcohol > water > diethyl ether
C. diethyl ether > ethyl alcohol > water
D. diethyl ether > water > ethyl alcohol

Answer 1

Hint: The intermolecular forces are basically attractive and repulsive forces that hold the atoms together within a molecule. These forces are dependent on boiling point, which vary when there is any change in boiling point.

Complete step by step answer:
- If we see the order of boiling point given in the question then it will be in the order of: water $\left( {{100}^{\circ }}C \right)$ > ethyl alcohol $\left( {{78.5}^{\circ }}C \right)$ > diethyl ether$\left( {{34.6}^{\circ }}C \right)$.
- Now, if we see that if the intermolecular forces are more then there will be more attraction between particles.
- This means that the attraction will not let the particle to separate from each other and will not let escape in vapour phase, and due to which the vapour pressure will increase and hence, the boiling point will increase.
- Hence, we can say that if there are more intermolecular forces present then the boiling point will be more. That is, intermolecular forces are directly proportional to boiling point.
- So, we can see that the order of boiling point is water > ethyl alcohol > diethyl ether. Hence, the order of intermolecular forces will be also the same as this order.

Hence, we can conclude that the correct option is (A) that the intermolecular forces will be in the order of: water >ethyl alcohol > diethyl ether.

Note: One should not get confused in the terms intermolecular and intramolecular forces. Intermolecular forces are those forces that are present between molecules. Whereas, intramolecular forces are those that hold the atoms together within a molecule. There are also several other properties like surface tension, melting point, viscosity that will increase with increase in the intermolecular force of attraction.