Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

If we talk about electric heating then we have simple elements in which we apply electrical energy which gets converted into the kinetic energy of the electrons which heats it up.

But while cooling, we need to take away energy from those electrons doing their dances, since we do not even have to apply energy and rather take it away it should have been easier but we know it is not.

Why is it easier to give free electrons kinetic energy than it is to take it away?

Similarly if we see on the reaction front exothermic reactions are much more easier to sustain and perform than endothermic ones, this also seems to show that endothermic reactions must somehow be difficult than exothermic ones in general.

Why does it seems so?

share|cite|improve this question
I think uncertainty principle will be under trouble, if you can convert all the kinetic energy of the electrons into some other form. – Immortal Player Jun 4 '14 at 8:38
@Godparticle : It's not about the entire energy, just like it is easy to heat elements to certain limit, it must be easier to cool them to certain limit. – Rijul Gupta Jun 4 '14 at 8:40
I didn't understand, why you think it is easier to heat than cool something. – Immortal Player Jun 4 '14 at 8:45
There are exactly as many endothermic reactions as there are exothermic ones, since very exothermic reaction in reverse is an endothermic reaction, and vice versa. The real question should be why it is often easier to set up for a reaction to run in the exothermic direction than for it to run in the endothermic direction; here the laws of thermodynamics give a precise answer. – Marc van Leeuwen Jun 4 '14 at 10:58
@MarcvanLeeuwen : Thanks for the suggestion – Rijul Gupta Jun 4 '14 at 11:01

It is easy to give something energy, but it is difficult to take it away, because you just can't "take away", you have to "make it give" you the energy. Normally you cool something by having something cooler that it can give it's energy to (Fridge :-P ). If you get really low, you can do Laser Cooling, which works because you make the particles give more energy back than you gave.

So, you can never "take away energy", only "give". For cooling, you need to "make the particle give".

share|cite|improve this answer

I want to point out, that we tend to live and think on the (rather) low end of the temperature scale.

You would run into the same kind of problem if you're at very high temperatures and would like to continue raising the temperature. At that point I'm sure it'll be easier to "take" energy away and thus reduce temperature.

share|cite|improve this answer
nice point made – Avik Jun 4 '14 at 10:34
There isn't any high end of the temperature scale, so this is a bit like saying the natural numbers we encounter tend to be at the low end of the natural number scale. – Marc van Leeuwen Jun 4 '14 at 22:22

I believe the question should be broken in two parts: (1) how to convert energy from or into heat, and (2) how to bring/take away the heat to/from the object you want to heat/cool down.

The process (2) is actually symmetrical whether you want to heat or cool: phenomena such as conduction or radiation give the same heat flow with a reversed sign whether the temperature difference is positive or negative.

So the asymmetry lies really in the energy conversion (1): we have many exothermic reactions at hand, and mostly rely on combustion, while sustained endothermic reactions are more difficult to exploit in engineering conditions.

share|cite|improve this answer
You helped me to improve my question, thanks a lot. I am editing it now. – Rijul Gupta Jun 4 '14 at 9:56

I would assume that entropy would be a large factor. In any conversion of energy from one form to another, there will naturally be some degree of waste heat (entropy) generated. Therefore, heating is like rolling something downhill- it's the "natural" tendency anyway. Cooling something generally involves moving heat up a gradient, which requires more energy because you're still generating waste heat.

In both circumstances, the overall entropy (assuming it's a closed system) must increase. In heating that works to your advantage, while in cooling you're fighting against it. As an example, if you take a refrigerator, thermally isolate it, and plug it in, eventually it'll overheat.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.