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idav
2008-Aug-05, 03:51 AM
Once again, my refutations of creationists in other places lead me to some decent questions. This is not really one of them. I understand it is the product of the sort of, top down, inference that the creationist is begging but anyways...

What is an example of a closed system in reference to thermodynamics?

As always, your knowledge and answers are greatly appreciated!

DrRocket
2008-Aug-05, 04:16 AM
Once again, my refutations of creationists in other places lead me to some decent questions. This is not really one of them. I understand it is the product of the sort of, top down, inference that the creationist is begging but anyways...

What is an example of a closed system in reference to thermodynamics?

As always, your knowledge and answers are greatly appreciated!


Most experiments in chemistry are conducted as closed systems. Closed here meanis that mass does not enter and leave the system. That is why many chemistry texts on thermodynamics emphasize closed systems.

Mechanical engineering texts on thermodynamics are more concerned with extraction of work from engines and turbines and therefore emphasize open systems.

Delvo
2008-Aug-05, 04:31 AM
If you include the flow of energy, there can't be any such thing as a truly absolutely closed system, not even one that's completely sealed against matter getting in or out. What you can get is one that's close enough that you can safely ignore the energy (or mass) that leaks into or out of it and still get answers that are accurate enough.

In other words, when the laws of thermodynamics that rely on closedness work well enough, the system is closed enough. When they don't, it isn't. No organism or ecosystem ever can be, though, because the amounts of matter and energy that constantly flow into and out of any organism or ecosystem are HUGE.

Jens
2008-Aug-05, 05:04 AM
If you include the flow of energy, there can't be any such thing as a truly absolutely closed system.

I think it could be argued that the universe may be a closed system, but I guess it isn't really known.

Drunk Vegan
2008-Aug-05, 05:55 AM
In other words, when the laws of thermodynamics that rely on closedness work well enough, the system is closed enough. When they don't, it isn't. No organism or ecosystem ever can be, though, because the amounts of matter and energy that constantly flow into and out of any organism or ecosystem are HUGE.

Agreed. Even vacuum in space isn't immune to energy being added or removed. A complete vaccum is composed, if I'm understanding what I've read correctly, of particles that are constantly appearing and disappearing from the observable universe every Planck length of a second.

Which is... weird. Is the only word. Where does it go to and where does it come from? Some other dimension which we can't detect? Another universe? Nowhere? I can't wrap my head around it.

idav
2008-Aug-05, 02:32 PM
Most experiments in chemistry are conducted as closed systems. Closed here meanis that mass does not enter and leave the system. That is why many chemistry texts on thermodynamics emphasize closed systems.

Mechanical engineering texts on thermodynamics are more concerned with extraction of work from engines and turbines and therefore emphasize open systems.
That's pretty much what I expected to hear.

What occurred to me during the my conversations was what Delvo was getting at. You can't really ever have a "isolated system" or "closed system" in nature in the macroscopic sense, ei and environment that is isolated from another environment. You can however have chemical mechanisms and reactions where only certain types of energy are relevant and thus might appropriately be examined in this respect as a closed system.

Thoughts?

Saluki
2008-Aug-05, 02:55 PM
One example of a system that is "close enough" for many purposes is a thermos bottle. In lab work, chemists use many similarly-insulated devices, such as calorimeters (http://en.wikipedia.org/wiki/Calorimeter), to approximate closed systems.

John Mendenhall
2008-Aug-05, 05:08 PM
One example of a system that is "close enough" for many purposes is a thermos bottle. In lab work, chemists use many similarly-insulated devices, such as calorimeters (http://en.wikipedia.org/wiki/Calorimeter), to approximate closed systems.

True.

Where it gets interesting is trying to design closed recycling starship systems. Over time, all systems leak. For example, you need to carry enough oxygen for the trip, and enough extra oxygen for the leakage, and remember that the extra oxygen containers will themselves leak, also, ad infinitum.

In the real universe, entropy rules.

Jeff Root
2008-Aug-05, 07:01 PM
If you include the flow of energy, there can't be any such thing as a
truly absolutely closed system, not even one that's completely sealed
against matter getting in or out. What you can get is one that's close
enough that you can safely ignore the energy (or mass) that leaks into
or out of it and still get answers that are accurate enough.
Often more practical, though, is a system in which the leaks can be
easily and reliably measured, or otherwise known and accounted for,
rather than ignored.



No organism or ecosystem ever can be, though, because the amounts
of matter and energy that constantly flow into and out of any organism
or ecosystem are HUGE.
The quantity is a problem in relation to tracking smaller transfers of
matter and energy, but I don't think it is the main problem. That must
be the distribution, variety, and subtlety of the matter/energy flows.
Accounting for the flow of solar energy into an ecosystem isn't difficult
because of the quantity; It is difficult because the energy is so widely
distributed and there are so many interdependent factors which modify
the rate at which it is taken into the system.

-- Jeff, in Minneapolis

mugaliens
2008-Aug-05, 08:37 PM
The simplest example of a closed system would be 2 moles of hydrogen and 1 mole of oxygen inside a perfectly insulated container. When they combust, you now have 1 mole of H2O, and an increase in temperature. Everything is contained within that closed system.

Naturally, no man-made system is truly closed, as there will be leaks of, say, heat, as no material is perfectly insulating. However, for the purpose of study, we can mentally construct such as system. Furthermore, once we've tested the system and know what those leaks are, we can factor them into our measurements and obtain very accurate information as to the nature of the process and it's outcome as if the system were truly closed.