Heat And Thermodynamics

[bryandaledc]

Who can give me a simple explanation about the relationship of thermodynamics

[sanctus]

Thermodynamics to me is hand-waving arguments which turn out to work, but never really clear (eg. I never understood what entropy is until statistical physics course). But you should post a bit more specifically what you are after.

[bryandaledc]

Thank you Sanctus, highly appreciated

[exchemist]

Thermodynamics to me is hand-waving arguments which turn out to work, but never really clear (eg. I never understood what entropy is until statistical physics course). But you should post a bit more specifically what you are after.

Oy! Describing thermodynamics as "handwaving argument" is preposterous. 

 

It is a highly mathematically exact and successful treatment of the relationship between heat and work and of energy transformations more generally. Its enormous successes underpin the whole of our industrialised economy.

 

The OP asks a huge question, admittedly, since it is not possible to give an explanation of thermodynamics in a paragraph on a discussion forum: there are thick university level textbooks devoted to it. 

 

By the way, I was interested to learn, only fairly recently, that the first law of thermodynamics (energy conservation) follows from Emmy Noether's Theorem, so that law is more than just empirically observed to be true. 

 

The Second Law (entropy increase in irreversible processes) is explained, once you have understood its basis in statistical thermodynamics, so that too is more than just empirically observed to be true.

 

If our OP wants to understand more about thermodynamics, perhaps it would be a good idea to try reading this simple link and then come back with more specific questions: http://www.physics4kids.com/files/thermo_laws.html

 

(My own thermodynamics is rusty, but one can't read chemistry without a lot of stat TD, so I ought to be able to help.) 

Edited May 21, 2016 by exchemist

[bryandaledc]

Thank you very much exchemist for giving that so nice explanation

[exchemist]

Thank you very much exchemist for giving that so nice explanation

Well it wasn't much of an explanation, more of a definition I suppose.

 

But if you want to talk more about it, I'd be happy to try to hold up my side of the discussion.  

[bryandaledc]

But still exchemist it really gave me a big help for the information, thanks again if you want give a bit of details about that topic I'm very much welcome for that

[sanctus]

 

 

Oy! Describing thermodynamics as "handwaving argument" is preposterous.

Super LOL. I agree it is harsh to say that, but really before you get into statistical thermodynamics you just get a working set of tools and ideas but can't really grasp why. I mean entropy was defined as "what transports heat". And you also start saying stuff about statistics and noether's theorem for saying that it is not presposterous.

[exchemist]

 

Super LOL. I agree it is harsh to say that, but really before you get into statistical thermodynamics you just get a working set of tools and ideas but can't really grasp why. I mean entropy was defined as "what transports heat". And you also start saying stuff about statistics and noether's theorem for saying that it is not presposterous.

Well the idea of energy conservation is pretty straightforward, surely? I mean, we accept other forms of conservation, e.g. momentum, without saying it's handwaving, don't we? I only mentioned Noether's Theorem as it seems to give an even firmer foundation for the idea, for those that really want to probe why the First Law is true. (By the way, please don't ask me about Noether's Theorem: I'm not enough of a mathematician to understand it properly.)

 

Entropy, dS =dQ(rev)/T,  is a harder concept to grasp, I grant you, until you have realised it is ultimately to do with statistics. But I'm not sure defining it as "what transports heat" is very helpful. Surely temperature is what determines the direction of heat flow, isn't it? I used to think of entropy as a measure of the unavailability of heat to do work. I think it sort of makes intuitive sense that high temperature heat is "uphill" compared to low temperature heat and as heat does work it runs downhill from higher temperature to lower temperature. The formula for Carnot efficiency of a heat engine makes this fairly evident: η =(Th -Tc)/Th . The smaller the temperature difference between the hot and cold reservoirs, the less work you can get out, so low temperature heat can only do work if you can find an even colder reservoir for it to flow into - and there is a limit to how cold a reservoir you can find. But I agree that it is really Boltzmann S =k lnW that ultimately explains what it is all about.  

[sanctus]

I guess I should define what I mean by "hand-waving": it is exactly what you do in the last paragraph (minus first and last sentence). What I mean instead of getting almost unequivocal interpretation and explanantion you have to find a way of thinking that explains it to yourself. Also note, I never said it didn't work:-).

And I guess I misquoted my college teacher, I just remember him using some analogy between electric potential and entropy (which kind of agrees with your interpretation).

[exchemist]

I guess I should define what I mean by "hand-waving": it is exactly what you do in the last paragraph (minus first and last sentence). What I mean instead of getting almost unequivocal interpretation and explanantion you have to find a way of thinking that explains it to yourself. Also note, I never said it didn't work:-).

 

And I guess I misquoted my college teacher, I just remember him using some analogy between electric potential and entropy (which kind of agrees with your interpretation).

OK fair enough, certainly my somewhat vague conceptualisation of entropy qualifies as "handwaving". 

 

By the way, where the hell are simple smileys in the list of emoticons on this site? There seem to be all sorts of bizarre thingies of questionable utility, but the one that really is useful doesn't seem to be there!

[sanctus]

Well I gladly would give up a standard smiley in favor of this one ;) : :rant:

So should be fine, others standard ones are: 

": )", etc. with no space i.e ":" + ["(", "D", ")"] and ";" + ")"  (we seem to have a limit on number of emojis I did not know about)

[exchemist]

Well I gladly would give up a standard smiley in favor of this one ;) : :rant:

 

So should be fine, others standard ones are: 

 

": )", etc. with no space i.e ":" + ["(", "D", ")"] and ";" + ")"  (we seem to have a limit on number of emojis I did not know about)

Sorry I'm still unclear. Are you saying there is a regular smiley or not and, if there is, where will I find it, please? When I press the emotican symbol I get a long menu but can't see it anywhere. Is it near the beginning, the middle, then end, or is it not there at all?

[sanctus]

Just type them like in sms (with no dashes) colon+closed parenthesis=standard smiley etc :)

[exchemist]

Just type them like in sms (with no dashes) colon+closed parenthesis=standard smiley etc :)

Ah OK so they aren't in the menu and I have to do manually. OK.