Question

Based on thermodynamics, why is a saturated fat a solid at room temperature and why does it have a higher melting point than an unsaturated fat?

Answer 1

as thermodynamics is depends upon change in G and G is an extensiv propperty means that it depends upon the quantity of matter present in the system

As saturated fats , have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogens possible. Since the fatty acids in these triglycerides contain the maximum possible amouunt of hydrogens, therefor ethey are called as saturated fats.

The hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fats solid at room temperature . because of better ,efficient , closely packing their melting points are high ( due to high Van der Waal interaction )

interaction

while in the unsaturated fats  have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or “kinks” in the shape of the molecules. Because some of the carbons share double bonds, they’re not bonded to as many hydrogens as they could if they weren’t double bonded to each other.Therefore these oils are called unsaturated fats.

Because of the kinks in the hydrocarbon tails, unsaturated fats can’t pack as closely togetheas compared to our saturated Fats , making them liquid at room temperature.

low melting point due to less efficient closely packing and weak Van der wall forces .