Chemistry - Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?

Solution 1:

No such liquid, safe or otherwise, can exist. Evaporation is a strictly endothermic process in all cases.

The change in state from liquid to gas is marked by the individual particles gaining enough translational kinetic energy to overcome the mutual attractions present in the liquid phase to "fly free" in the gas phase. It is logically inconsistent for a substance to increase its internal energy and release energy to the surroundings as heat in the same process.

In order to achieve both evaporation and a release of energy, one would have to find a liquid that reacts to (a) release heat and (b) form gaseous products. The energy required to move from the liquid to the gas phase is substantial; more than likely the only reactions exothermic enough to provide a net release of heat are combustion reactions.

I somehow doubt dumping a flammable liquid into your thermostat, inserting a wick, and lighting it on fire is a satisfactory solution for you.

Solution 2:

Silly question, but why can't you get the thermostat adjusted to the temperature you want? You've got a nice control mechanism built in to the room and you want to tinker with it... to make it hotter in winter and colder in summer.

But if there is some reason you can't get the thermostat adjusted, instead of using an exothermic evaporating liquid (as hBy2Py says, because evaporation is increasing the kinetic energy in each molecule compared to the bulk liquid it's got to be endothermic) why not get a peltier cooler such as at and magnet it onto the panel in the right place. Feed it the appropriate (low) voltage one way it heats up the panel, reverse the voltage it cools it down.

That's far safer than evaporating acetone or ether!

Solution 3:

Can't you use something like a hair drier? It's a bit noisy but you don't need much time to trigger it.
Else, you can use the coffee machine warm water, you just need it to touch the panel, not pour it onto it...
I second the heating pad idea.
If I would follow your principle I would find a way to have some evaporated liquid condensate at thermostat plate level, in a reverse way to what you have (inside a bottle, glass is a good thermic conductor). You can evaporate a few water inside a bottle then let it cool by transfering its energy to its environment. Problem being that it will also actually warm the room.

Solution 4:

Forgive me for saying, but this feels like a problem statement in which the setup of the question inadvertently obscures the actual solution space. You state a number of constraining requirements, that other answers have dutifully adhered to by telling you there is no solution, but the actual problem does not seem to have those constraints.

For example is the phase of matter truly a requirement? Must it be a liquid? Must the mechanism of action be limited to evaporation? Are those really requirements?

It seems to me there is nothing about the explanation that requires those constraints. It seems to me that the constraints are actually: something that is clever, not unsightly or likely to lead to damage, and of course effective at making the thermostat turn on the air conditioning. In other words something as clever as your acetone solution, which is in fact quite clever.

However, as stated the question reads like "I'm hot, how do I build a fire that's cold?" And so, of course, hBy2Py is absolutely correct to tell you that there is no such fire.

Could the answer not be in the form of a solid? Maybe a mixture of particulate solids? Perhaps fine particulates that could even be aerosolized?

Because if that's the case I'd draw your attention to rust, iron oxide. You know the kind of thing you might find in disposable hand warmers. A fine particulate mixture of iron, activated charcoal, salt, vermiculite, and water. Cheap, safe, exothermic, and clever.