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I am looking for an alternative to the sodium acetate reaction used in e.g. heat packs. I need something similiar but that generates more heat, so that I could for instance warm 200ml of water to a temperature of 37 °C.

So is their any safe and reusable reaction as used in heat packs but that generates more heat?

NOTE: I am a beginner when it comes to chemistry.

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    $\begingroup$ I am afraid the requirements (reusable, safe, exothermic enough, closed system ) almost mutually exclude themselves. Sodium thiosulphate pentahydrate gives up to 48 deg C, but you would need a really big pack for warming 200 mL water to 37 deg C. I am not sure about comparision of generated heat per gram of this and sodium acetate. $\endgroup$ – Poutnik Feb 23 at 11:29
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    $\begingroup$ A rechargeable battery, connected to a heater, can do the job. But then the chemistry is hidden away inside the battery. This is a common fate of real world chemistry: it is one of the major unsung heroes that makes modern life possible. $\endgroup$ – Ed V Feb 23 at 13:16
  • $\begingroup$ I was hoping to not use any battery, would like a heat pack-like solution. I guess I could use several small heat packs to heat the water? $\endgroup$ – scorp1on Feb 23 at 14:53
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    $\begingroup$ It all depends on how easy it is to re-charge the heat pack. For a short period of time, my supermarket sold self-heating cans of coffee. You activated the internal heating mechanism, which caused calcium oxide (“quick lime”) to react with water. This is a highly exothermic reaction that surrounded the separate internal compartment of coffee. An environmental disaster and market failure. But you can regenerate calcium oxide from calcium hydroxide by application of heat. Lots of heat. So it is reversible, but not so practical outside a lab. $\endgroup$ – Ed V Feb 23 at 15:59
  • $\begingroup$ By the way, the self-heating coffee can was not gigantic, the volume of coffee was above 200 mL, and the final temperature was well above body temperature. I bought one can for use as a demo in class. As for taste, I have had better coffee ... $\endgroup$ – Ed V Feb 23 at 16:05

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