Question

Why does ethanol have a higher boiling point than ethane?

Answer 1

Hint: Think about the molecular structure of both the molecules and also the reactivity of the atoms that are involved in making the molecule. Consider the type of bonding these differences in electronegativity may contribute to.

Complete step by step solution:
Ethane has the molecular formula ${{C}_{2}}{{H}_{6}}$ and ethanol has the molecular formula of ${{C}_{2}}{{H}_{5}}OH$. Here, we can see that an extra oxygen atom is present in ethanol due to the presence of the hydroxyl group.
The higher boiling point of ethanol indicates that it has stronger or a larger number of bonds than ethane. Let us look at the structures of both the molecules before we determine why ethanol has a higher boiling point.

Despite the greater number of bonds present, this will not have an effect on the boiling point since the constituent molecule does not dissociate. The difference in electronegativity between carbon and oxygen will create a partial negative charge on oxygen.
This will cause the oxygen to form intermolecular bonds with the hydrogen atoms on the other molecules to form hydrogen bonds. The hydrogen atoms that are involved in the hydrogen bonds are the hydrogen atoms in the hydroxyl group and not the hydrogen atoms attached to the carbon atoms. The difference in electronegativity of carbon and hydrogen is very less, so partial charges will not develop on them. A visual representation of that is:

This hydrogen bonding is absent in the ethane molecules. Hence, its boiling point is lower.

Note: Remember that when a stronger or larger number of bonds are referred to in the context of boiling or melting points, they almost always refer to intermolecular bonding and not intra-molecular. Melting or boiling is a physical change and not a chemical one, so the molecule does not dissociate and the intramolecular bonds are not taken into consideration.