Freethought & Rationalism Archive

modig · 06-17-2003, 05:22 PM

For those of you out there who actually understand what entropy is, please tell me if this statement sounds correct.

"""
A misconception that often comes up when people talk about evoltuion/creation is assuming that DNA represents a big decrease in entropy, simply because it is "ordered." In reality, DNA really isn't much if any less entropic than a rock at the same temperature, and is much more entropic than a cold rock.

The same can be said for a whole living organism, that they are more entropic than a rock at the same temperature, and definetly much less entropic than the Carbon Dioxide gas that most of the Carbon they are made of comes from.
"""

Thanks people, I'm pretty sure this is correct, but I don't want to get caught making a mistake, even a small one, so point out anything.

Dr.GH · 06-17-2003, 06:51 PM

The amount of energy used to sustain life is consistent with the 2nd law as it �consumes� more energy than it generates, and is not in conflict with the 2nd law as the extraterrestrial source of energy (the sun) produces much, much more energy than is consumed by life.

take a look at these web sites (they can help more than I can):

http://www.acchurch.com/reading/evolution.php

http://www.2ndlaw.com/evolution.html

Jesse · 06-17-2003, 07:34 PM

Is it really right that an organism has no lower entropy that a rock made up of an equal number of atoms at the same temp., pressure, etc.? Life forms contain all sorts of complex molecules which would break down fairly quickly if not constantly replenished by external energy, while a rock could be kept in complete isolation for a while without really changing much. I guess that could have something to do with the molecules in a rock having higher activation energy than the molecules in living organisms, and thus being able to stay in a state of higher potential energy (and thus less entropy) for longer in isolation. Still, the statement sounds a bit fishy to me.

modig · 06-17-2003, 08:38 PM

Well in general solids have less entropy than liquids or gasses, and since a body is largely made up of liquid, it should be more entropic than a solid of comparable size and temperature.

So... anybody else? I just want to be sure about this before I go about posting it as part of an argument.

nermal · 06-17-2003, 08:56 PM

How about "entropy only applies to closed systems"?
If you are talking about the entire cosmos as a closed system, then entropy would be a good point of discussion. When you are talking about cells, rocks etc. you are talking about different levels of order within a system, which is meaningless in terms of entropy.

Ed

modig · 06-17-2003, 08:59 PM

I don't think that Entropy applies only to closed systems. The second law of thermodynamics is generally defined for a closed system, but that doesn't mean entropy is meaningless for an open system.

Imagine a thermos with water in it, essentially a closed system. It has a certain amount of entropy. Now, I open the thermos, does it suddenly become immpossible for me to know the entropy?

nermal · 06-18-2003, 02:50 AM

Quote:

Originally posted by modig
Now, I open the thermos, does it suddenly become immpossible for me to know the entropy?

My initial impulse is to say yes, it does, or more accurately, entropy is no longer a property of the system in the thermos. Admittedly, I'll have to look into this, it's been several years since I've studied Thermo, and I haven't applied it in 10 years.
Meantime, others may have the answer for me.

Ed

Goober · 06-18-2003, 07:24 AM

No, it is not impossible to know the entropy of the water. If the flask held one litre of water at 25 degrees, it's entropy would be about 3.8 kJ/K. This value does not change if the lid is taken on or off.

The entropy of a system is always a property of that system. The closed open/system applies to entropy changes. If the system is closed, any the total change in entropy in the system must be positive or zero.

If the system is not closed, the entropy change in the system can have any value, provided the entropy change in the entire universe is positive, where the entropy change in the universe is the sum of the changes in the system and it's surroundings.

The earth is not a closed system, obviously, so it is possible for entropy to decrease on earth, provided this entropy decrease is offset by an entropy increase that is equal or larger elsewhere in the universe.

Quote:

A misconception that often comes up when people talk about evoltuion/creation is assuming that DNA represents a big decrease in entropy, simply because it is "ordered." In reality, DNA really isn't much if any less entropic than a rock at the same temperature, and is much more entropic than a cold rock.

This whole concept is confused I'm afraid. A piece of DNA may have more entropy than a piece of rock of the same weight, but that does not matter. Comparing DNA to rock doesn't tell you anything.

To form a long DNA molecule from it's components will involve a large entropy decrease - but this does not matter at all because it also gives off heat, which increases the entropy of the surroundings.

A simple organism becoming a complex organism involves an entropy increase because the complex organism needs more energy to be built and to maintain itself, and all of this energy comes from processes that cause larger entropy increases elsewhere.

Jesse · 06-18-2003, 08:35 AM

Quote:

Originally posted by Goober
To form a long DNA molecule from it's components will involve a large entropy decrease - but this does not matter at all because it also gives off heat, which increases the entropy of the surroundings.

A simple organism becoming a complex organism involves an entropy increase because the complex organism needs more energy to be built and to maintain itself, and all of this energy comes from processes that cause larger entropy increases elsewhere.

But that "elsewhere" will mostly be the environment external to the organism itself. The quote was just talking about the entropy of an organism vs. the entropy of a rock, not about how much entropy was created in forming them.

The original quote seems to ignore the point that molecules have a characteristic entropy at a given temp and pressure--that's the entropy that's filed under "dS" in the Gibbs equation dG = dH - TdS which is used for chemical reactions (the dS would be the difference between the entropy of the reactant molecules and the entropy of the products). This www.2ndlaw.com page describes roughly what it means to talk about the entropy of molecules:

Quote:

The Gibbs equation is only concerned with macrothermodynamics, with what we can measure in the lab rather than what is happening down there inside the molecules during chemical reactions. What IS entropy change from the viewpoint of a molecule? Boltzmann and "microthermodynamics" deal with that. (You've heard a lot about it in other sections of this Web site.) To begin with, depending on their temperature and solid/liquid/gas state, all molecules need a certain amount of energy to move and rotate and vibrate internally, in addition to the large amount of electronic energy in their bonds that holds them together. S(298oK, formation) in your textbook tables -- that's really dS(from absolute zero, formation) because entropies are assumed to be 0 there -- measures all those kinds of energy "in a bundle". So TdS in the Gibbs equation is the amount of energy a mol of product molecules needs to exist at a temperature T compared to one of reactant molecules. (Give them more energy and they scoot around faster because the added energy goes into their translational/rotational/ vibrational modes. Heat them up to a high enough temperature and you even boost them to an excited electronic state where bond breaking can occur.

I don't know where you could find the entropy of a DNA molecule, but I expect it would be fairly low compared to the entropy of the atoms that make it up, since DNA tends to break down in isolation--in living organisms it requires all sorts of helper molecules to keep it stable.

It would be hard to calculate the entropy of an organism, but what you might be able to do is just calculate the entropy of all the molecules that make it up, and compare to the entropy of the molecules that make up a rock. I suspect the entropy of organism-molecules would be lower. And of course, there are probably a lot more ways to arrange the positions and momentums of the rock molecules (ie a lot more microstates) to get a macrostate that looks like a rock than there are to arrange the molecules making up an organism into a macrostate that looks like a living, breathing life form (as opposed to a random stew of molecules). This would make the entropy of an organism still lower, although this aspect of the problem would probably be almost impossible to calculate.

modig · 06-18-2003, 11:19 AM

Well... my argument that an organism would have lower overall entropy than a rock of similar size and temperature is simply that most organisms are mostly liquid (water) and liquids in general have more entropy than solids. I'm fairly sure that's solid, but... it wouldn't hurt to get some numbers involved. Maybe I'll relearn how to do it, and see what happens.

06-17-2003, 05:22 PM	#1
modig Junior Member Join Date: Dec 2002 Location: Santa Clara, CA/Cottage Grove, OR Posts: 6	Entropy (clarification) For those of you out there who actually understand what entropy is, please tell me if this statement sounds correct. """ A misconception that often comes up when people talk about evoltuion/creation is assuming that DNA represents a big decrease in entropy, simply because it is "ordered." In reality, DNA really isn't much if any less entropic than a rock at the same temperature, and is much more entropic than a cold rock. The same can be said for a whole living organism, that they are more entropic than a rock at the same temperature, and definetly much less entropic than the Carbon Dioxide gas that most of the Carbon they are made of comes from. """ Thanks people, I'm pretty sure this is correct, but I don't want to get caught making a mistake, even a small one, so point out anything.

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06-17-2003, 06:51 PM	#2
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	The amount of energy used to sustain life is consistent with the 2nd law as it �consumes� more energy than it generates, and is not in conflict with the 2nd law as the extraterrestrial source of energy (the sun) produces much, much more energy than is consumed by life. take a look at these web sites (they can help more than I can): http://www.acchurch.com/reading/evolution.php http://www.2ndlaw.com/evolution.html

06-17-2003, 07:34 PM	#3
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Is it really right that an organism has no lower entropy that a rock made up of an equal number of atoms at the same temp., pressure, etc.? Life forms contain all sorts of complex molecules which would break down fairly quickly if not constantly replenished by external energy, while a rock could be kept in complete isolation for a while without really changing much. I guess that could have something to do with the molecules in a rock having higher activation energy than the molecules in living organisms, and thus being able to stay in a state of higher potential energy (and thus less entropy) for longer in isolation. Still, the statement sounds a bit fishy to me.

06-17-2003, 08:38 PM	#4
modig Junior Member Join Date: Dec 2002 Location: Santa Clara, CA/Cottage Grove, OR Posts: 6	Well in general solids have less entropy than liquids or gasses, and since a body is largely made up of liquid, it should be more entropic than a solid of comparable size and temperature. So... anybody else? I just want to be sure about this before I go about posting it as part of an argument.

06-17-2003, 08:56 PM	#5
nermal Veteran Member Join Date: Mar 2003 Location: Colorado Posts: 1,969	How about "entropy only applies to closed systems"? If you are talking about the entire cosmos as a closed system, then entropy would be a good point of discussion. When you are talking about cells, rocks etc. you are talking about different levels of order within a system, which is meaningless in terms of entropy. Ed

06-17-2003, 08:59 PM	#6
modig Junior Member Join Date: Dec 2002 Location: Santa Clara, CA/Cottage Grove, OR Posts: 6	I don't think that Entropy applies only to closed systems. The second law of thermodynamics is generally defined for a closed system, but that doesn't mean entropy is meaningless for an open system. Imagine a thermos with water in it, essentially a closed system. It has a certain amount of entropy. Now, I open the thermos, does it suddenly become immpossible for me to know the entropy?

06-18-2003, 11:19 AM	#10
modig Junior Member Join Date: Dec 2002 Location: Santa Clara, CA/Cottage Grove, OR Posts: 6	Well... my argument that an organism would have lower overall entropy than a rock of similar size and temperature is simply that most organisms are mostly liquid (water) and liquids in general have more entropy than solids. I'm fairly sure that's solid, but... it wouldn't hurt to get some numbers involved. Maybe I'll relearn how to do it, and see what happens.

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