Final answer:
The melting point of a fatty acid decreases as the amount of double bonds increases.
Step-by-step explanation:
The melting point of a fatty acid decreases as the amount of double bonds increases.
This is because the presence of unsaturation (double bonds) in the fatty acid molecule causes a pronounced bend in the structure, resulting in a reduced contact area between molecules. This reduces the intermolecular attractions (London dispersion forces) and weakens the interactions between molecules, causing the fatty acid to have a lower melting point.
For example, vegetable oils, which have a higher amount of unsaturated fatty acids, are liquids at room temperature due to their lower melting points. In contrast, animal fats, which have a higher amount of saturated fatty acids, are solids at room temperature.