In this question we have to get the reasons to have higher melting point of acetamide (CH₃CONH₂) than that of water (H₂O).
The reasons are-
1. The molecular weight of acetamide is more than that of water.
2. Acetamide can form strong dimeric six (6) member intermolecular hydrogen bond.
We know the boiling point of a compound depends upon its molecular weight, as the molecular weight increases the melting point also increases. In case of acetamide the molecular weight is 59 g/mol whereas for water it is 18 g/mol. Thus the boiling point of acetamide should be more than water.
There is a strong effect of hydrogen bond on the boiling point of a compound. As the strength of the hydrogen bond between the molecules of a compound increases the boiling point also increases. Now between water and acetamide both form hydrogen bond as shown in figure 1 and 2 respectively.
But the hydrogen bond between the acetamide molecules are strong six membered hydrogen bond than the chain hydrogen bond found in water as shown in the figure.
