Why are vegetable oils a liquid at room temperature?

Answer 1

Vegetable oil has a lower melting point compared to animal fat.

Answer 2

Vegetable oil is composed of unsaturated fats, meaning there are double bonds between the carbons within the triglycerides that make up the fat. Animal fats, however, are saturated fats, meaning there are no double bonds in the triglycerides.

Answer 3

Well, semantically speaking, if it's liquid at room temperature it's an oil and if it's solid at room temperature it's a fat, so in that sense the question answers itself.

However, the reason these very similar compounds have different melting points has to do with their structure. Both fats and oils have a long chain of carbon atoms in them (actually, they have three, but it's simpler if we just think about one).

In some, that long chain is saturated, meaning it has all the hydrogen atoms it can possibly hold. This means that every carbon-carbon bond is free to rotate, and it allows the chain to wiggle around into the best possible conformation to pack with all the other chains. This means it's easier for them to pack together into a solid form.

In others, that long chain is unsaturated, meaning that at least two carbons have a double bond between them. Double bonds cannot rotate, so that introduces a point in the chain where you can't just bend it any which way. This makes it harder to pack them together, so they tend to stay liquid at lower temperatures.

More than one double bond ("polyunsaturated") makes it even harder to pack the chains, so they have even lower melting points.

Also, there's one more subtle factor: a double bond can be in one of two possible conformations, either cis (shaped kind of like a fat V with a flat bottom) or trans (a kind of zig-zag shape, a little bit like the S in the logo of the band KISS or the double-sig markings worn by Nazi SS officers). The trans form packs a little more easily than the cis form does, which is why you hear people talking about "trans fats" ... everything else being equal, the trans form will melt at a higher temperature than the cis for.

Vegetable oils are often polyunsaturated, animal fats are typically saturated. If you see the term "hydrogenated" or "partially hydrogenated" it means that the (usually vegetable) oil or fat has been treated in a way that removes the double bonds, making it more like an animal fat. The one health advantage that hydrogenated vegetable oils like Crisco have over animal fats such as lard is that they contain no cholesterol.

Answer 4

Vegetable oil has a lower melting point compared to animal fat.

Answer 5

they are unsaturated fats, which means the molecule does not have Hydrogen's attached to every Carbon on the fatty acid chain

Answer 6

Canola oil is a liquid at room temperature because it contains polyunsaturated fatty acids.