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Posted By prads
Can someone give me a layman's explanation of the second law of thermodynamics with an example of energy transfer in the Environment??
Regards,
Prads
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Posted By D. Hilton
Entropy:
Flow of heat from an area of higher temperature to an area of lesser temperature until a state of balance.
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Posted By Robert K Lewis
In terms of health and safety environment. The amount of chaos in the system will aways increase unless acted upon by an external source to produce negative entropy.
In broad terms the sense is that the environmental temperature will even out to give a uniform entropy across the globe providing that the global system is isolated from all other inputs. The exisitence of the poles etc suggest that the earth is not an isolated system. Question is then "Can there truly be Global Warming?" Or in fact is it a local condition?
Bob
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Posted By Coshh Assessor
I think D. Hilton has quoted the first law of thermodynamics there.
The second law says that an isolated system will become more disordered over time. This does include other types of energy eventually being irreversibly converted into heat.
An example in the environment is that if a contaminant gets into the sea, it will disperse and the longer you leave it the harder it is to collect up again.
Another example is that when energy is transmitted or used in any way (eg through electricity lines, or converting gas into electricity) you lose some of the useful energy in the process.
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Posted By J Knight
Bob,
The Earth is absoultely not an isolated system; it receives massive inputs of energy from the sun. And yes, the globe can warm very easily (as indeed it can cool); in the first case the poles get warmer as well as everywhere else, in the second case the tropics get cooler as does everywhere else.
Take some wood; a highly ordered arrangement of long-chain molecules. Add oxygen, and the product will be a much less highly ordered collection of shorter chain molecules, some in a gaseous form, and a relase of heat into the environment. This is an entropic transormation,
John
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Posted By D. Hilton
Coshh
I think you will find that I quoted the 2nd Law.
The 1st law does not provide the information of direction of processes and does not determine the final equilibrium state. Intuitively, we know that energy flows from high temperature to low temperature. Thus, the 2nd law is needed to determine the direction of processes.
Regs
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Posted By D. Hilton
By the way
your contaminant and the sea example is Diffusion
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Posted By Descarte
The 1st Law states Energy/matter cannot be created nor destroyed (so where did matter come from?)
The second law shows that energy within a closed system will degrade over time. An example is the impossibility of perpetual motion. In terms of engineering or even safety this means energy will always flow out of a system (hot to cold, never cold to hot) and you will need to keep inputting energy in to keep it constant. (yes this means the universe will run out of energy eventually)
The third law is about entropy or randomness, which decreases as tempertaure reaches absolute zero, mainly centred around the movement of atoms - Hot move fast, slow move slow or vibrate slightly, absolute zero dont move at all.
So to answer your question - In our environment the we gain energy from the sun and loose energy to space.
Des
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Posted By Coshh Assessor
I think Prads would be better off asking on a science forum!
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Posted By J Knight
Descartes,
Quite possibly from the collision of two branes separated along a fourth dimension which collide once every several trillion years, if you're into M (or string) theory that is. Or maybe a random big bang. In other words, thermodynamics only applies to closed systems; M theory posits two systems which are individually closed but open with respect to each other, the big bang posits the inception of a fresh closed system at a state of minimum entropy,
John
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Posted By Robert K Lewis
Descarte
The 3rd law is also known as the Nernst heat theorem, states that if one could reach absolute zero, all bodies would have the same entropy. In other words, a body at absolute zero could exist in only one possible state, which would possess a definite energy, called the zero-point energy. This state is defined as having zero entropy.
My statements are in fact concerned with the second law which is related to the increasing entropy of a system over time unless there is an external action that can produce a negative entropy eg a refrigerator. Work has to be input into a system in order to maintain the entropy at equilibrium. Without such actions the system will tend to have an even spread of entropy throughout.
Bob
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Posted By D. Hilton
Prads
I have already given a layman's answer, here it is again in other terms,
The second law is expressed mathematically in terms of the concept of entropy. When a body absorbs an amount of heat Q from a reservoir at temperature T, the body gains and the reservoir loses an amount of entropy S=Q/T. Thus, in a reversible adiabatic process (no heat change) there is no change in the total entropy. If an amount of heat Q flows from a hot to a cold body, the total entropy increases; because S=Q/T is larger for smaller values of T, the cold body gains more entropy than the hot body loses. The statement that heat never flows from a cold to a hot body can be generalized by saying that in no spontaneous process does the total entropy decrease.
COSHH next time don't bother to think on my behalf. It never ceases to amaze me that the H&S profession will attempt to bluff and spoof even when they know they cannot demonstrate competence in a subject, perhaps that is why so many have the opinion that is commonly held.
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Posted By Ron Hunter
I'll get my coat.
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Posted By John Richards
Hawking posits a universe where "negative" energy is balanced by "positive" energy. The result being a universe where the net energy balances out as zero.
First law:
Energy can neither be created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
Second law:
The entropy of an isolated system consisting of two regions of space, isolated from one another, each in thermodynamic equilibrium in itself but not in equilibrium with each other, will, when the isolation that separates the two regions is broken so that the two regions become able to exchange matter or energy, tend to increase over time, approaching a maximum value when the jointly communicating system reaches thermodynamic equilibrium.
Third law:
As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.
Personally, I just hope to be able to pay the gas bill before entropy increases again.
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Posted By prads
Thanks everyone for your replies !
I wanted to put the second law in the perspective of environment (earth) as a closed system and the analogy of effluents to sea is good, where you are saying that concentrated energy (effluents) moves to a lower concentrated region (sea) and in this process most of the energy becomes useless (by dispersing into the sea) and eventually it will completely become useless over a period of time. This is not reversible, these dispersed (effluents) cannot flow back and make up the highly concentrated effluent.
Did I read you correct Coshh? Thanks a lot Hilton, for your scientific explanation.
Regards,
Prads
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Posted By Flic
I like the Flanders and Swann approach:
'heat cannot of itself pass from one body to a hotter body ......'
'heat won't pass from a cooler to a hotter...'
'cos the hotter body's heat will pass to the cooler......'
So your fridge does not spontaneously get cooler - you have to use energy and some cunning engineering to drain heat from it. On the other hand a hot body will spontaneously shed its heat to cooler surroundings.
Flic
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Posted By Coshh Assessor
Yes, in the case of the contaminant (let's say it's oil) dispersing in the sea (mainly by wave action with some contribution from diffusion - oil stays where it is on still water!) the tendency for things to lose their ordered arrangement whenever there is change (entropy to increase) overcomes the preference of the oil molecules to stick together and avoid the water (that is, the surface energy of the oil).
Incidentally, I am no bluffer - I studied chemical thermodynamics in some depth as an undergraduate, although in the intervening years some details have faded as they always do. The statement of the second law that I learned was that the entropy of an isolated system increases over time, or "everything always gets worse". The catch of course is that there are no isolated systems other than the entire universe.
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Posted By John Richards
Your problem being that the earth is not a closed system.
The earth is the receiver of some 174 petawatts of incoming solar radiation.
It also receives incoming cosmic radiation from the rest of the universe.
Have a read:
http://www.digital-recor...l/pdfs/life_on_earth.pdf
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Posted By John Richards
Left to its own device, and without any energy input from any source, a 'fridge will attain the temperature average for the universe. 2.7 degrees above absolute zero.
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Posted By Yossarian
Yes John, but by the time it has done that, you may find that the food has gone off!
;-)
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Posted By Flic
As will all of us!
Flic
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Posted By Robert K Lewis
Like COSHH assessor I too do not bluff as my early career was as a chemical engineer and thermodynamics were bread and butter issues. Yes the global environment is not a closed system hence my comments and some concerns that Global Warming is not the straight line claimed by many in the current debate.
I personally feel that there is no easy application of thermodynamics to the environment as there are so many complex variables. I prefer to take a much more holistic view with a broad brush sweep of the issues. The actions of humankind are increasing the total entropy of the planet, in a multiplicity of ways such as polution, use and dispersion of resources, agricultural practices etc in such a manner that only a large energy input from humanity will arrest or reverse some of the changes. Some changes are however irreversible.
Bob
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Posted By Ron Hunter
Prads, your sea/effluent dilution analogy is flawed. Concentrations are known to often arrive back at dangerous levels via complex food chains. A similar counter-argument could be posited for mutagenic effects.
Now, where's my coat...............
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Posted By Flic
But, Ron, the pollutants don't spontaneously concentrate themselves. They come back in concentrated form as a result of expenditure of energy.
I don't think the example is flawed, but here we are comparing the refrigerator which cools food to a temperature below that if its surroundings, with an expectation that the food will spontaneously become cooler than its surroundings.
Flic
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Posted By Robert K Lewis
I think we are coming close to the "All swans are white" argument. Question can we expend energy in a refrigerator and still not decrease entropy - answer is yes if the refrigerator does not work properly!!
We are entering the realms of semantics here and the end is fruitless as I will merely slip into reader response readings of the text to completely disrupt any inteneding meaning by an author in order to read support for my theories in all that I read. There is thus no truth in any of the arguments given only an acceptance of certain facts at certain points in time.
Bob
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Posted By D H
Lost me now Bob - Ill get my coat as well
Dave
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Posted By Robert K Lewis
I am about to put mine on as well
Bob
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Posted By Coshh Assessor
Whatever happens, if anything happens, the total entropy goes up. That's the law! That doesn't preclude it being decreased in some part of the system and living organisms are very good at doing this. The living things have low entropy but by living they cause the entropy of their environment to increase (at the most basic level, by emitting heat).
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Posted By Descarte
Or is it that just by observing them you are effectively increasing their entropy as per heisenbergs principle?
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Posted By Ron Hunter
Heisenberg, eh? Next we'll be citing Schrodinger!
I'll get my cat...............
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Posted By Robert K Lewis
Now we have the single quantum in two places at once to worry about. This thread is now getting silly:-)
Bob
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Posted By Descarte
No but I could quote Pavlov, then my dog could chase your cat (whilst salavating of course)
Des
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Posted By Coshh Assessor
Is it nearly Friday yet?
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Posted By John Packer
I think so, therfore it must be
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