Question

Ethylene glycol (HOCH₂CH₂OH) is the major component of antifreeze. It is a slightly viscous liquid, not very volatile at room temperature, with a boiling point of 198°C. Pentane (C₅H₁₂), which has about the same molecular weight, is a nonviscous liquid that is highly volatile at room temperature and whose boiling point is 36.1°C. Explain the differences in the physical properties of the two substances.

 

 

Answer 1

As you can see from the formula, ethylene glycol is an alcohol with two OH groups. This hydroxyl groups are responsible for the formation of intermolecular hydrogen bonding which results in strong interaction with each other. This requires high energy to overcome hydrogen bonding and form vapors. Hence it has high boiling point. The liquid is viscous due to strong cohesive forces.

In pentane, there is no hydrogen bonding seen. Molecules interact with each other via weak van der Waal\'s forces. Hence very less heat energy is required to vaporize it. Hence it has low boiling point. The liquid non viscous due to less cohesive forces between them.

As you can see from the formula, ethylene glycol is an alcohol with two OH groups. This hydroxyl groups are responsible for the formation of intermolecular hydrogen bonding which results in strong interaction with each other.