0
$\begingroup$

As I've learnt, systems in the Universe always tend to increase their entropy since it provides a larger number of availiable microstates for energy to be distributed and is hence statisticaly preferred.

Also, colder objects tend to have a higher entropy since they want to break free of contraints applied due to the low temperature(such as being in a solid or liquid state) and hence "dissipate" energy and become more disordered.

But then, this would mean that systems always want to attain a higher state of disorder(which they could do by attaining a higher temperature, right?) which would imply that objects must never cool down since cooling down increases the stability at a molecular level and must be thermodynamically unfavourable, which is quite an obvious contradiction to what we observe in real life.

I am aware of the equations regarding change in entropy of universe, System and surroundings. My question is, shouldnt it intuitively unfavourable and hence never occur?

$\endgroup$
2
  • $\begingroup$ I am aware of the equations regarding change in entropy of universe, System and surroundings. I feel like if you did understand this you would have your answer. $\endgroup$ – BioPhysicist Nov 4 '19 at 15:14
  • $\begingroup$ The question is rather unclear. E.g. in the 2nd paragraph your write "[...C]older objects tend to have a higher entropy [compared to what???]" -- hotter objects? However, I believe that you have two problems: (1) The total energy is a constant. It's impossible that all parts of a system are getting hotter -- unless we add energy. (2) If we perform work, it's possible to reduce the temperature of one part -- think of a refrigerator. Nevertheless, the entropy of the total system (refrigerator + environment) increases. $\endgroup$ – Semoi Nov 4 '19 at 18:21
2
$\begingroup$

Also, colder objects tend to have a higher entropy

That is not correct.

A colder object has lower entropy than a hotter object, all other things about the two objects being equal. It is the change in entropy of the colder object that is greater than the hotter object, for a given transfer of heat, again all other things about the two objects being equal.

Since your initial assumption that colder objects have higher entropy is incorrect, the contraction you later identify based on that initial assumption is also incorrect.

Hope this helps.

$\endgroup$
5
  • $\begingroup$ Ah thanks I had quite a big misunderstanding between entropy and change in entropy! But,since hotter objects have more entropy, they are thermodynamically favoured and hence all objects must go on heating indefinitely? But to the same statement of mine, objects lose heat by radiation as long as they are above 0K, isnt that a contradiction again? $\endgroup$ – Siddharth Bhat Nov 5 '19 at 14:37
  • $\begingroup$ @SiddharthBhat Your welcome. Glad it was of help. $\endgroup$ – Bob D Nov 5 '19 at 14:38
  • $\begingroup$ @SiddharthBhat Objects don't necessarily go on losing heat by radiation as long as they are above 0 K. That's because while they are radiating heat out to objects of lower temperature heat is being radiated to them by objects of higher temperature until thermal equilibrium is reached. The theory is (though there is disagreement) eventually everything in the universe will reach the same temperature for thermal equilibrium throughout the universe, the so called "heat death", with no more thermal driving forces left. But it wouldn't be reach 0 K. $\endgroup$ – Bob D Nov 11 '19 at 14:08
  • $\begingroup$ And that's because to reach 0 K you need to transfer heat to something at less than 0 K, which is the theoretical minimum temperature you can have. $\endgroup$ – Bob D Nov 11 '19 at 14:09
  • $\begingroup$ Ahh so the overall entropy change of the system must be considered here, am I right? $\endgroup$ – Siddharth Bhat Nov 14 '19 at 18:01
0
$\begingroup$

As I've learnt, systems in the Universe always tend to increase their entropy since it provides a larger number of availiable microstates for energy to be distributed and is hence statisticaly preferred.

Note, this holds for closed systems.

In thermodynamics are you aware of black body radiation?? That is what is missing from your arguments.

The thermal radiation leaving the body increases the entropy of the system "Body+radiation" exponentialy, due to the large number of microstates. In addition black body radiation cools the body because energy leaves the body with the radiation.

Thus you are using wrong inputs in your argument: cooling increases entropy, and cooling means lower energy levels of the atoms with the black body radiation.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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