Thermodynamics in a nutshell...if that's even possible.

Factual Questions
1

When I was at a wedding a few weeks ago, our table got into a light conversation about thermodynamics (yes, that’s almost comical). I was referencing the guys hand on his beer bottle relating to the law that states that heat moves towards areas of lesser heat, and so, his hand was heating his beer bottle.

We established the 1st law as being basically “energy cannot be created nor destroyed”, and then came to an impasse. I asserted that there were at least three laws, and my friend (an ME) admitted that he was ashamedly ignorant of the third law, and doubtful of a possible fourth.

IMO, heat transfer and the inability to create or destroy matter, are the two most basic tenets of the laws of TD. The other two, seem to be less clear to the layperson. I read the Wikipedia site on thermodynamics, and it didn’t really solidify the concepts of the zeroth law, nor the fourth law to my satisfaction.

So, I call upon the Dope to provide an explanation that might be easy for the technical layman to understand, in regards to the laws of thermodynamics.

It can be done. Stephen Hawking did a great job of it when he write ABHOT.

2

Zeroth law If A is as hot as B and B is as hot as C then A is as hot as C (seems obvious but needed to be stated)
First law Cant create any more energy
Second law Chaos always increases with time
Third Law As the temperature decreases to absolute zero, the entropy (chaos) of a system decreases to zero
(These are a bit simplified but essentially right)

3

There are 4 generally agreed upon laws of thermodynamics. Oddly, though, the one written last is really the first or fundamemtal one. Since the 1st, 2nd and 3rd were already well established, it is known as the 0th (Zeroth) law. It is the principle you sparked the conversation with, namely that heat flows from warmer to cooler, or more rigorously, thermal masses in contact will come to an equilibrium.

I forget where I first heard it, but it related the 3 laws to a game of poker in this way;
[ol]
[li]You can’t win. (Energy can’t be created or destroyed, merely changed in form. So you can’t get more out than you put in.)[/li][li]You can’t break even. (Entropy increases, so you can’t even get out all the energy you put in.)[/li][li]You can’t quit. (Entropy is positive at any temperature above absolute zero, so you continue losing even if you don’t play)[/li][/ol]

It’s helped me remember them for too many years.

ETA: Upon reading SCM1001’s post, I screwed up the 0[sup]th[/sup].

4

The first and second law are both part of classical thermodynamics, and should probably be sufficient information for a layman to understand the subject. After the first and second laws, you begin to get into nuclear and chemical reactions, which begin to act in ways a layperson may not consider intuitive.

“the zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.”
In other words, if A=B, and A=C, then B=C, where A, B, and C are measured in units of temperature.

The first law, matter or energy can be neither created or destroyed, IMHO, does not need an extensive proof. You simply can’t create or destroy matter or energy. It’s just not possible. IOW, the energy of a closed system is conserved, weather it be your car (fuel = energy (heat and power) + exhaust), your body (food = energy (heat, power, metabolism) + “exhaust”), or the universe.

To expand on the second law, which is perhaps the most important one, entropy is always increasing. Entropy is basically “unavailability to do work”. IOW, the work has already been done. For example, when burning a match, entropy is set to be equal to zero when you have a match ready to be lit (it’s never zero, because we don’t have a datum for zero. We can only compare relative values. Zero is easy to compare to.) After you light the match, the work the match can do is gone, so entropy becomes higher.

Another way of looking at the second law would be in a Carnot cycle. The Carnot cycle describes the most efficient possible way to gain energy from a hot reservoir transferring energy to a cold one. In an internal combustion engine, the fuel burns and heats up, creating some temperature X. The exhaust is at some temperature Y, and the incoming fuel/air mixture is at temperature Z. Theoretically, heating a gas from Z to X, and cooling it to Y, using a variant of the ideal gas law, and knowing the temperatures, you could get an idea of how much energy was produced to force the piston down. However, some of that energy must also be used to heat the engine block up, so it can’t be used to push the piston down*. Basically, the system will never be as efficient as it theoretically could be. That is the heart of the second law.

The third law basically defines absolute zero as the temperature at which molecular movement stops, and states that it cannot be reached by any finite number of processes.

5

I love the poker analogy.

Oh, remember that the first and second laws only apply if you’re talking about a defined system. You can’t cheat and pile in energy into a system when no one is looking without accounting for it. It’s violating the 1st law - and that makes Lord Kelvin (et al) cry.

Basically, it’s a way of account for all the energy in a particular system. Lets look at a match (ooh!) and define the system as ‘the match plus the air around it (and something to strike the match with if you want to split hairs)’. You can’t light a match and violate the 1st & 2nd law. There’s potential energy in the form of chemical bonds. When lit, uses the surrounding oxygen to burn the chemical energy in the matchhead and wood - converting the energy into heat and light. First laws says that the total energy converted into heat and light cannot be greater than the total chemical energy. The 2nd law says this conversion isn’t 100%. The system boundry prevents you from using a blowtorch to burn it and claim you got 2000% efficiency.

This comes into play whenever someone comes up with a perpetual motion machine. Either it’s cheating and the true system boundry is much larger than it seems (eg Herod’s fountain uses atmospheric pressure), or it’s gonna eventually run down due to friction (2nd law baby!).

6

Nothing to really add here, I just heard my name called repeatedly.

Well, I suppose I could mention our Perfect Master’s take on the 2nd Law, as my sig relates…

7

I like to think of it statistically, of all the possible states of a system, the ones with order are exceedingly improbable. That’s why, even though it’s possible, you don’t have to worry about all of the air molecules in a room moving to one corner of the room, leaving you to suffocate in a vacuum.

8

Heat cannot of itself pass from one body to a hotter body,

Heat won’t pass from a cooler to a hotter,
You can try it if you like but you’d far better not-a,
'Cos the cold in the cooler will get hotter as a rule-a,
'Cos the hotter body’s heat will pass to the cooler.

As reported by Michael Flanders and Donald Swann.

9

To clarify a bit (and because this is so often misunderstood especially in creationism debates)…

Increase of entropy is not a one-way process. The key principle that often gets left out is that entropy can be decreased (and does so naturally) but requires energy input to do so.

10

This is important. The second law is a statistical law. What it more precisely states is that the average entropy of a closed system is always increasing. That doesn’t mean that entropy is increasing everywhere. You can have a local decrease in entropy so long as there’s a greater increase in entropy that causes it.

11

To put an example to that, consider a heat pump. Heat-energy–that is, the random kinetic motion of atoms or molecules–is absorbed from a low temperature reservoir and “pumped” via a compression and expansion cycle into a higher temperature reservoir. In this way, you can seemingly paradoxically make use of the 30°F outside ground temperature to help warm the air in your house to a comfortable 68°F. You can even do this using less energy than it would take to directly warm your house to the same temperature; hence, a heat pump can have an over-unity efficiency (usually referred to as “efficacy” so that people don’t wigged out) over a direct heat cycle. (The reason a ground source or water source heat pump works so well is that while the temperature might be low, the actual amount of energy is more concentrated by the density of soil or water in comparison to air.)

Of course, you are not, despite occasional claims by foolishly misguided free energy enthusiasts, getting something for nothing; the extra heat-energy is simple reorganized in a less random fashion, i.e. all concentrated in your house rather than distributed outside. And the trade-off is that global net entropy still increases; the amount of work done on the working fluid in the compression cycle by the compressor motor results in greater exergy (negative entropy) loss than is gained by reorganizing environment heat. So the Second Law still holds, James Clerk Maxwell slumbers peacefully in his grave, and nobody needs to pull the daemons away from their drinks. Turn a heat pump around and you get the common refrigerator cycle which cools off your car in summer and keeps your beer cold; in this case, you pump heat-energy out of the container and convect/radiate it into the environment by the coils on the back.

Now, we keep throwing around this term, “entropy” (or exergy) but what does this actually mean to you, the consumer? While most people like to focus on Law #2–and it is a pretty impressive statement which, correctly phrased, has something useful and mathematically explicit to say about any type of work cycle–the third law is a lot more interesting to me. In general concept, entropy is the amount of energy that exists in a sytem but isn’t available to do useful work. Why isn’t it available? Because you have to have a gradient or a differential between one area of your system and another in order to get energy to move or flow and thus do something. If I put a (hypothetically weightless) balloon in a room in which the temperature of the air inside the balloon is the same as the ambient temperature, it just sits, going nowhere. However, if I heat up the balloon (or cool the room), it will expand and rise because the temperature differential causes the air inside the balloon to expand and do work on the air outside, pushing it away and seeing the reaction force by the denser air outside. (I’m assuming you’re going this in someplace with gravity and air pressure gradients resulting therefrom.) Similarly, heating gas in a Stirling recipricating piston engine causes it to expand and push the piston because the pressure on the other side is lower.

So entropy isn’t just about the amount of energy you have in one spot, but how it compares to the amount of energy you have around it, and how that is organized. This in turn creates gradients which are not just useful, but in fact (in any real world situation) will automatically cause work to be done whether you like it or not. Hence, we have hurricanes and tornados, which result from a low-entropy distribution of energy to a higher entropy system (once they’ve exhausted themselves). If you have an insulated box where the temperature is exactly the same everywhere, nothing happens on the overall level, no matter how hot it is inside the box, because there is no gradient. Never mind that the individual molecules are bouncing around like children on a sugar high; the distribution is completely random (or perhaps I should say more appropriately “normal”) and you can’t get enough of them to go in any one direction for long enough to do anything useful. And you thought herding cats was difficult?

Local entropy can be decreased, but only by fussing about somewhere else, resulting in a net global increase in entropy. And you can’t stop it or get off the ride, ever. Well, except inside of a black hole, where local entropy is theoretically maximized, but nobody wants to go there, at least no one you really want to be associated with.

People frequently ignorantly invoke the laws of thermodynamics in common discourse as both an analogue and to “explain” why something is or is not popular. The most egregious, in my mind, is the use of misuse of the concept of entropy to “refute” evolution and Darwinist selection by asserting that living systems somehow function in violation of the statistical mechanics principles of thermodynamics. Never mind that not only does every biological mechanism or cycle that we’ve ever examined adhere precisely to thermodynamic principles (indeed, the discovery of respiration was due to the application of the laws of conservation and thermodynamics), but that life itself functions like a very complex heat pump cycle, moderating the flow of energy in order to do useful work. A proper understanding of thermodynamics reinforces the comprehension of biological processes as fundamentally mechanical/chemical interactions rather than contradict them.

Unfortunately, it is a topic only properly taught at the collegiate level. and then only in the natural sciences and engineering disciplines, even though the underlying principles can be readily grasped by anyone with an understanding of basic algebra. And look as I might, I can’t find a single pop-science or rudimentary level book on thermodynamics. The closest I can get is Van Ness’ Understanding Thermodynamics, and even that is too mathematical for a nontechnical audience.

Stranger

12

One of the best examples where the entropically favored result is counterintuitive is Peter Stangs work with self assembly of small molecules. He synthesizes (well his students do anyway) small molecules that make up the corners of a geometrical shape. Intuitively, the idea that these peices would “fall” into organized geometrical structures seems unlikely, but other organizations of these molecules require the solvent to order itself to accomodate them. So the apparently ordered geometries are actually the most random organization available.

13

While I haven’t read it - and am unlikely to feel the need to - I notice that Peter Atkin’s latest, Four Laws That Drive The Universe, is newly out in the UK and looks like that it fits that requirement. Short, bite-sized chapters on each of the laws of thermodynamics.