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When we talk about cooling, like from an air conditioner, we talk about heat transfer. Heat is transferred from a warmer body to an already cool body. But can cooling be achieved in an isolated substance without heat transfer?

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When we talk about cooling,like in air conditioner, we talk about heat transfer. Heat is transferred from warmer body to already cool body. But can cooling be achieved in an isolated substance without heat transfer?

In physics, heat is the process of transfer of energy, it is not the same definition as we use in ordinary life. Once inside the box, we really should say amount of internal energy, not heat.

If the substance (or system) has a certain amount of internal energy, and is perfectly insulated (or isolated) from the outside world, it will never lose or gain internal energy.

But the key word here is perfectly, which is not achievable in practice because of the laws of thermodynamics. Eventually, internal energy will leave the substance because we cannot make perfect insulators, even in theory.

The temperature of an isolated system could increase or decrease. Just the energy is conserved. Thanks to Jan Bos for pointing this out.

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    $\begingroup$ The temperature of an isolated system could increase or decrease. Just the energy is conserved. $\endgroup$ – Jan Bos Nov 3 '16 at 11:41
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Heat is a transfer of energy from one body to another......it is the transfer of the vibrational and translational kinetic energy (and all other energies which are due to motion of molecules) of the molecules from one substance to another.

So technically, an ISOLATED system by definition cannot involve heat exchange at all.

But there is such a thing as adiabatic cooling. It involves reduction in temperature of the fluid (gas or liquid) by letting it do work on its surroundings thereby letting it relax more...which reduces its temperature. But if you are thinking about a perfectly isolated room with immovable insulating walls (also with you inside), there is no way you can achieve cooling by adiabatic expansion of the air inside.

Update

@Jan Bos

I was thinking more like a room with rigid insulating walls with OP and some air inside. But no arguments, an endothermic reaction will definitely decrease the surrounding temperature. You are right.

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  • $\begingroup$ For example a endothermic reaction in the isolated system will decrease the temperature and I believe the answer to OPs question is yes it is possible to cool an isolated system without heat transfer with the outside. $\endgroup$ – Jan Bos Nov 3 '16 at 14:10

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