Ever use a pump to inflate a tyre? I've given myself small burns by underestimating how much heat was released by gas compression. When you release the pressure, the gas cools, like when using a spray can - it can also get very cold.

Different gasses will change temperatures at different rates when pressurised, this is given by the Joule Thompson coefficient Hydrogen is a notable one, as it has a negative coefficient (i.e. it does the opposite of most gasses) near room conditions.

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Sodium acetate is the chemical in the reusable handwarmers.

You can coat a reactive chemical in a protective coating, then like popping a balloon, the pressure breaks the coating and triggers the reaction. The easiest example of this is putting an oxidizer and a reductant in the same bag.

There are lots of exothermic crystallization reactions where the pressure nucleates a crystal in supersaturated solution. You can control that pressure using engineering of the container, but it's not unique to the actual chemical.

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For all things not including (Hydrogen, Neon, and helium) they usually will not cool down when compressed. That's not how pressure and temperature are related for most substances.

A perfect example is the ideal gas law PV=nRT

Where:

P= pressure of the observed system

T= temperature of observed system

As you can see, Pressure becomes divided by Temperature or vice versa (depending on what you're solving for), which means they are directly proportional (instead of inversely proportional, where if pressure went up, the temperature would drop)

Now, I can go more into detail as to WHY this physically happens (hint, temperature is a measure of energy in a system, as you compress a system things, they bump more, create more friction, etc.) but I did not want to just unload a ton of info if you didn't need it to answer what you are actually asking

Edit: accounted for the Joule Thompson effect as described below in comments

Anything with a negative jt coefficient will get colder when compressed, eg nitrogen and hydrogen over their relevant temperature ranges.

http://en.wikipedia.org/wiki/Joule-Thomson_coefficient

This genuinely never came up in school even once, and I'm a chemical engineer! Very interesting concept, thank you! I'll edit my reply

It appears it would be useful for refrigeration or leak finding when combined with thermal imaging. Microleaks are extremely hard to detect even with leak detectors

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Thanks for your input!

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Is this correct? My understanding is that when a gas exapands it draws in energy from the surroundings. Which is why its previous vessel cools down like how you mentioned the can getting cool, but the gas itself gained energy. Meanwhile, a gas compressor is used in AC units to force the gas flowing through the line to release its heat which is then dissipated across a radiator with air flowed over by a fan. Am I missing something?