Wikipedia:Reference desk/Archives/Science/2016 April 14

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April 14

Specific heat of Pepsi

What is the specific heat of Pepsi? It's easy to find pages on Google that address this issue, e.g. [1], but for some reason my browser's throwing a fit and refusing to open anything. It's almost all water, so the answer should be really close to one joule per millilitre, but the corn syrup and other ingredients presumably alter it slightly, and I'm not sure whether they'd raise it or lower it, and I don't know how much. Nyttend (talk) 01:58, 14 April 2016 (UTC)

PS, bonus points if you can also find the specific heat of Coca-Cola. Nyttend (talk) 02:01, 14 April 2016 (UTC)

@Nyttend: The powerpoint you linked mentioned Pepsi One since it has one calorie (4184 J, which can boil 10 ml of water according to the powerpoint). I think you need to specify how much Pepsi you're referring to though. Like one 12oz can? EvergreenFir (talk) Please {{re}} 04:04, 14 April 2016 (UTC)

How would the specific heat change by volume or mass? Isn't the specific heat of water always one joule per millilitre, regardless of the number of millilitres? Nyttend (talk) 04:12, 14 April 2016 (UTC)

Yeah, I think you're right there. Honestly I doubt it differs much from water though. This page says it's 4.16 J/ml (slightly less than water). Found a list of liquids' specific heats here, but no soda (List of foods here if you're interested). This link might be interesting but need to sign up to download the files. EvergreenFir (talk) Please {{re}} 06:13, 14 April 2016 (UTC)

To add, it seems adding things to water lowers the J/ml needed. Compare milk and sea water to fresh water in the list of liquids linked above. EvergreenFir (talk) Please {{re}} 06:19, 14 April 2016 (UTC)

Just riffing on an idea here. Heat_capacity#Theory_of_heat_capacity notes that heat capacity is related to, among other things the degrees of freedom of the molecules of the substance. When you dissolve something in water, you need to solvate the particles, water molecules participating in solvation lose some of their relative freedom of motion; reducing the degrees of freedom thus reduces the specific heat capacity. This matches what happens to the entropy of the water molecules: solvation always causes a loss of entropy in the solvent (solvation is spontaneous though when the resulting increase in entropy of the solute counteracts this effect). For the same reasons. --Jayron32 14:45, 14 April 2016 (UTC)

The trouble with Pepsi is that it's not a simple homogeneous material - the dissolved CO2 complicates both the measurement and practical utility of the specific heat number. SteveBaker (talk) 14:07, 14 April 2016 (UTC)

So you're asserting that a long-opened, "flat" can of Pepsi would have a different specific heat than an unopened can with all the CO2 still in it? That makes sense, this page [2] says that specific heat of a mixture is the (mol fraction weighted) mixture of the specific heats. And then that says that the flat can of pepsi has a higher specific heat than the unopened can. That equation also supports the claim that many/most foods that are water+other stuff will have a lower specific heat than water. Water is second only to ammonia in this list of specific heats [3]. SemanticMantis (talk) 14:38, 14 April 2016 (UTC)

I expect the specific heat is complicated - probably non-linear - because the solubility constant of carbon dioxide in water depends on temperature. As you add heat, you necessarily change the mole fraction of the mixture (you can't get around this problem!) So, your specific heat number has a temperature dependency, and hysteresis, which makes it a lot less useful. Nimur (talk) 14:55, 14 April 2016 (UTC)

Right. The dependence on time and temp makes sense, but I'll explain the hysteresis (since I didn't understand what you were talking about at first). Consider two cans of pepsi (A,B) opened at time t_0 and temperature T_0. Can A is heated until time t_1, and has temperature T_1, and then is held at that temp. Can B is heated until time t_2>t_1 and temperature T_2>T_1, then cooled to T_1 at t_3. At t_3, A and B can have different specific heats, because they took different routes to the same temperature, even though they have the same temperature and time-since-opening. This is because can B will have lost more CO2 in the same time period (having spent some time at a higher temp), and hence have a higher specific heat. Neat. SemanticMantis (talk) 16:17, 14 April 2016 (UTC)

See my comment above, as well. Dissolved CO2, like any solute, will reduce the degrees of freedom in the solvent because some of the solvent molecules are required to "solvate" the dissolved particles, these particles are essentially "locked in" to a specific arrangement around the solute particles ("solvent cages" is a common way to describe this). This resulting loss in degrees of freedom directly impacts the specific heat of the solvent by lowering it, in all cases. Agreed that the math is very complicated and probably nonlinear, but conceptually, all solutions should have a lower specific heat than the parent solvent should for those reasons. Specific heat depression could probably be counted among the Colligative properties of solutions for that reason. --Jayron32 15:22, 14 April 2016 (UTC)

Drugs to reduce inhibition/anxiety when approaching women

collapsed for space, suggest readers follow IP 178's own advice below
The following discussion has been closed. Please do not modify it.
This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~ Tevildo (talk) 21:53, 14 April 2016 (UTC) What about advice on building tall structures or Tesla devices. Can we ask Qs about those?--178.99.232.11 (talk) 23:52, 14 April 2016 (UTC) Wikipedia does not tell people how to cure their personal illnesses, or how to solve their legal problems. At the reference desks, otherwise, we are here to provide you with links to articles, either inside Wikipedia or outside Wikipedia, to help you research answers to your questions. --Jayron32 23:56, 14 April 2016 (UTC) Note that it is usually possible to craft a question that people can respond to with links that may provide you with relevant information, without running afoul of the prohibition. One red flag to avoid is any mention of any real-life situation prompting the question. It's all a bit legalistic and sometimes gets a little silly IMO, but them's the rules. --Trovatore (talk) 23:58, 14 April 2016 (UTC) @Jayron You miss my point. Perhaps intentionally?--178.99.232.11 (talk) 00:00, 15 April 2016 (UTC) I'm not here to get points. I'm here to provide references to help you with your research. --Jayron32 00:02, 15 April 2016 (UTC)

See talk page.--178.99.232.11 (talk) 00:03, 15 April 2016 (UTC)