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A friend of mine, based on casual observation, believes that coffee will cool faster than ordinary hot tap water. Being curious about this I have tried to investigate it myself, but I'm not well versed in physics and thermodnamics. Also, I know that there are many variables to this, so I will attempt to ask the question as specifically as possible:

I have 8oz of water (we can assume that it is impure, but we can not know what those impurities are) that is heated to 200 degrees F in a microwave (let's say we have a really precise microwave that can do that easily) and that is then placed in a standard, throw-away styrofoam coffee cup.

I have an exact duplicate scenario, except that this time we will also brew coffee in the water for several minutes, filter out the coffee using a standard coffee filter (we can assume some coffee particles remain in the water, but we can not know anything about those coffee particles) and then re-heat the water to 200 degrees F before adding it to the foam coffee cup.

If each of these coffee cups are then placed on separate tables in a room-temperature room (let's say 70 degrees F) and allowed to sit, undisturbed, will the liquids cool at roughly equivalent speeds (i.e., will the water and the coffee reach 180 degrees F at roughly the same time) or will one cool faster than the other?

For either scenario, why?

If there's any clarification or wording choices that should be changed, please let me know as I am genuinely curious. My guess is that there's something to do with the specific heats begin different, and that the surface tension of the coffee mixture will be disrupted due to the coffee particles. But, again, I don't really know :-)

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Dissolving things in water does change the specific heat and the conductivity (see e.g. engineeringtoolbox.com/sodium-chloride-water-d_1187.html), so it's possible the cooling rate would change though probably not by very much. –  John Rennie Nov 3 '13 at 16:19
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