[Lrich]

Two identical canisters containing equal masses of noodle soup and coffee are set to an equal initial temperature. Which will cool to room temperature quicker?

I honestly believed that I had this question completely understood, but I am beginning to second guess myself. The substance with the higher heat capacity will cool at a slower rate, that being said, I thought that since the noodle soup would be more dense it would cool at a slower rate and thus have a higher heat capacity, but I am not sure anymore.

Any explanation would be appreciated.

[Corribus]

To a first approx, I wouldn't say density and volume will matter. (They certainly will, and especially surface area will affect the heat transfer rate. But problems like this typically try to keep things simple.) So: heat capacity. I think it's safe to assume that coffee is essentially like pure water. Noodle soup will have a lot of starch, plus carrots and peas. You can find the heat capacities of those here:

http://www.engineeringtoolbox.com/specific-heat-capacity-food-d_295.html

Does this help at all?

[Borek]

Very hand wavy, but interesting.

Assuming similar heat capacities (the water is the main ingredient in both cases, so while obviously there are differences, they are not large) I would assume heat transfer to teh surface to be the limiting factor. Coffee easily mixes and the convection will be fast. Thick soup, full of noodles on the other hand...

[Corribus]

Yeah, that's a good point, Borek.

However I don't think the difference in heat capacity would necessarily be negligible. Depends on the soup, of course, but a thick chicken noodle can have a crap load of starch - both in the form of noodles as well as a thickener added to the broth. Plus fat and protein.

Ultimately it would come down to what would win out: a substance with good convection but high heat capacity or low convection and low heat capacity. Probably it will depend on what the heat capacity actually is - there will probably be a balance point below which heat capacity is the driving factor. Also, the more noodles and other solids, the greater the impact of convection.

As it happens, I have brought some thick chicken soup with me to work for lunch today. Maybe I will try to sneak some on the DSC.

[Lrich]

I'm still very confused. I thought that after the initial post and looking at the specific heats of starch, I figured that the answer would be coffee. But now thinking about what Borek has said, I am no longer sure.

[Corribus]

I think this is one of those questions where the point is just to test how you're thinking. There isn't necessarily a universally correct answer.