Silica
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Looking for the right exothermic reaction
Hi guys!
I have a bit of a puzzle that I haven't been able to solve, so I decided to ask on this forum:
I'm looking for a substance(s) which would generate decent amount of heat when mixed with water (obviously exothermic reaction). My aim is to heat up
1dl of water from initial 20 degrees of celsius to roughly 85 degrees of celsius. The net mass of the end products, including the water, shouldn't be
more than 125g. Furthermore the formed solution should be safe for human consumption, and it shouldn't produce any precipitate. I already studied the
CaO, CaCl2, Li2O (just a few to mention), and most common acids/bases: obviously these would generate lot of heat when mixed with water, but I found
that either the formed solution is harmful for humans or there is precipitate formed or the the overall mass is too high. Any help or suggestion on
how to proceed with this problem would be highly appreciated. Thanks!
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elementcollector1
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From a practical standpoint, traditional methods of heating win out over chemical methods due to versatile means of manufacture (in fire's case, at
least) and availability of reagents (or, in this case, fuels). But I'll treat this as a puzzle irrespective to practicality, because it's more fun
that way.
The 'safest' chemical that undergoes significant exothermic reaction is sodium acetate crystallizing from supersaturated solution. However, this is
neither safe for human consumption (unless you can deal with the contents of your stomach rapidly solidifying) nor particularly pleasant to ingest, so
that one's out.
Many anhydrous chemicals (copper sulfate, magnesium sulfate, and others) heat up when introduced to water. Of these, magnesium sulfate would probably
be 'best,' but again, it's not exactly pleasant.
Technically speaking, introducing any base (i.e. antacid, others) to your acidic astrointestinal fluids would result in heat being generated, meaning
that even calcium carbonate could suffice depending on how much you used. Unfortunately, this results in a lot of CO2 generation...
It's an interesting question, and I'm not sure there's an actual answer to be found. Anyone else want to take a crack at it?
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Silica
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Thank you elementcollector for such a swift reply!
You are right, the traditional means of heating surely wins out the chemical way, but I’m intentionally looking the chemical way. Let me explain a
bit more what I’m actually trying to achieve:
Biodegradable and edible pouch in which the reagents are stored -> the pouch is dropped in a beaker that contains 1 dl of water at NTP conditions
-> the protecting film quickly dissolves -> reagents become exposed to water -> instant, but not too violent exothermic reaction -> ~1dl
of hot water.
This would be great way to brew some coffee while hiking. Just grab some water from the river into your mug and toss in the pouch (of course the pouch
would also contain some instant coffee powder). No fire, no additional appliances, and best of all, no waste produced.
The energy required to raise 1 dl of water from 20 ℃ to 85 ℃ is about 27 kJ. 25g of CaO would do the trick, but the solution would become too
alkaline, and a nasty precipitate would also be formed. CaCl2 would also produce enough heat but the solution wouldn’t be drinkable either. The
supersaturated sodium acetate is quite interesting. It has some applications in food industry (mostly regulating the acidity), and I’ve seen it
being used in hand warmers, but as you said that wouldn’t be exactly pleasant to drink either.
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Fulmen
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Honestly, if I knew the solution I wouldn't tell you for a million dollars. That's a product that would make me a fortune.
Besides, it can't be done. If it could someone would have figured it out decades ago.
We're not banging rocks together here. We know how to put a man back together.
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LearnedAmateur
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You’d probably be better off studying a reaction as opposed to exothermic dissolution because depending on what you employ, you may need far less
than some salt. Keep with the idea of dissolvable pouches but with two parts for two reactants. Instead of dissolving it into the drink though, which
would probably be disgusting, maybe have another pot into which the water is heated and then add the drink container to that - I get you want to save
as much space/weight as possible but there’s no point if it can’t be consumed!
Potassium permanganate and diluted glycerol could be used in such a manner, since we know that the two can be used to start a fire when pure - instead
of that outcome, the oxidation reaction should just generate lots of heat instead. Plus, the KMnO4 has several other survival uses so it’s always
handy to carry some when out in the wild.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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XeonTheMGPony
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2 words: Hand warmers.
Carbon
Salt
Iron
Military had this solved years ago with field rations
Mg
Fe
NaCl
C
https://en.wikipedia.org/wiki/Meal,_Ready-to-Eat
https://en.wikipedia.org/wiki/Flameless_ration_heater
So just use biodegradable outer shell, a sachet of CaO in gell cap, user puts in their metal cup with their coffee mixed add water and wait
[Edited on 4-4-2018 by XeonTheMGPony]
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crystal grower
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I agree with XeonTheMGPony.
You can also use maybe a bit "upgraded" version of sodium acetate heating pad (with non-toxic encapsulation). You just initiate the crystallization
and put it inside you coffee cup.
It's also reusable which is a + I guess.
[Edited on 4-4-2018 by crystal grower]
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