The Laws of Thermodynamics

If one looks around the Internet, he or she can find a multitude of pages that state the laws of thermodynamics; so why add one more?  I've been writing a lot of posts on thermodynamics, but nowhere have I given a concise statement of the laws; also, I am not always happy with how the laws are described.  So this post is my contribution.

The Zeroth Law of Thermodynamics

The zeroth law states:

If two bodies are in thermal equilibrium with a third body, then they are in thermal equilibrium with each other.

The Third Law of Thermodynamics

The Third Law of Thermodynamics states that it is impossible to reach absolute zero in a finite number of steps. A shortcut way to remember the law is "you cannot leave the game."  An alternate shortcut to remember the law is "let's keep score" which is based on the fact that the third law provides the foundation for thermodynamic temperature scales.

The Heat Death of the Universe

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Time's Arrow. The previous post is essential to understanding this post.

In most of the discussion of nonsense in this series, the nonsense stems from a poor understanding of physics.  This post introduces some nonsense that must be taken seriously.  Perhaps, this nonsense, also stems ultimately from a poor understanding of physics.  The people with the poor understanding this time, however, are some of the most brilliant minds in physics.

The School-Book Story

This discussion starts with the school-book story of the heat death of the universe.  By calling it the "school-book" story I do not mean to pooh-pooh it too much.  In fact, it is most likely the correct story.  Much of this post, however, will focus on caveats and complications to the story as it is usually told.

In thermodynamics, the universe is defined as the system and its surroundings.  We have seen that the second law requires that for any change the total entropy of the system and the surroundings must increase or stay the same.  As time goes by, therefore, the entropy of the universe increases.

Time's Arrow

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Second Law, Microscopic Reversibility, and Small Systems. The previous post is essential to understanding this post.

Why does time move forward instead of backward? In the spatial dimensions, one can move left or right, up or down, backward, or forward.

Time, on the other hand, has a preferred direction. Why is that so? The underlying physics does not seem to have a preferred direction, but time does.

The Second Law, Microscopic Reversibility, and Small Systems

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Second Law, Radiative Transfer, and Global Warming.

On a small scale, individual physical events are reversible; yet on a macroscopic scale, it is not so.  I used to find that confusing.  I'd like to try to cut through some of the confusion.  In so doing, the underlying mechanism of the second law may become clearer.

Figure Source (Monopoly by Hasbro).

Petagrams of Carbon

Sometimes carbon dioxide is referenced in units of ppm, and sometimes it is referenced in petagrams of carbon.  What are the meanings of these units and how does one convert between them?

In a previous post I explained how to convert to and from units of ppm.  The current post explains the units petagrams of carbon, and how to convert from ppm to petagrams of carbon.

The Second Law, Radiative Transfer, and Global Warming

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Spontaneous Change and Equilibrium.

Does global warming violate the second law of thermodynamics?  Such a claim may seem strange.  The idea that the vast majority of physical scientists would subscribe to an idea that somehow violates a fundamental law of thermodynamics on its face seems odd.  Yet, such a claim is often made by people calling the science behind global warming into question.

Spontaneous Change and Equilibrium

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Free Energy.

Diamond turns spontaneously into graphite; yet we may have to wait longer than the lifetime of the universe to see such a change.  Hydrocarbons are spontaneously oxidized into carbon dioxide and water; yet gasoline requires a source of heat before it burns.

Free Energy

This post is part of a series,Nonsense and the Second Law of Thermodynamics. The previous post is entitled Entropy as Religious, Spiritual or Self-Help Metaphor.

You cannot get something for nothing, and the term "free energy" does not mean energy that has no cost.  Rather it refers to energy that is available to do something useful.  The use of the word "free" is in the sense of "liberated."  Free energy is energy that can be liberated to do something useful.

We know that the second law places limitations on how much energy can be used to do useful work.  In most situations, some of the energy must be dissipated as heat that cannot be used to do something useful.  The portion of the energy that can do something useful is the free energy.

At constant volume, the free energy is the Helmholtz Free Energy, given the variable A.

Enthalpy

This post continues a tangent  from my series on the second law of thermodynamics.  It discusses another quantity in thermodynamics, but it is necessary before I can get to the next post in the series, which is on free energy.

This post discusses the term enthalpy.

At constant pressure the change in enthalpy is the heat transferred to a system.

      ΔH = q  at constant pressure.

Heat is not a state function, but enthalpy is.

Second Law Poll

The purpose of this post is to document the final results of a poll on the site.  I do not intend to comment on the results until I conclude my series on the second law of thermodynamics.  It is worth noting at this point that there is no clear consensus on the correct answer from respondents.

 I think that this fact is reflective of the state of confusion that exists in public discourse regarding the second law of thermodynamics.

The poll asked the respondents to pick an option to complete the statement:  "The second law of thermodynamics states:"

The option were:

• The disorder of the universe must increase.
• You can't win.
• The entropy of an isolated system must stay the same or increase.
• The entropy of a closed system must stay the same or increase.
• Heat cannot be transferred from a cold body to a hot body.
• The entropy of the world must increase.
• Let's keep score.

The results are shown in the following figure with truncated responses:

The First Law of Thermodynamics

I need to take a tangent from my series on the second law of thermodynamics and discuss the first law of thermodynamics. 

Heat is not a conserved quantity.  Work is not a conserved quantity, but the sum of heat and work is a conserved quantity. The first law is related to the law of conservation of energy; in fact it is one case of that law.

Entropy as a Religious, Spiritual or Self-Help Metaphor

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Second Law and Creationism.

While browsing around the Internet for misuses of the term "entropy," I found some examples of the use of entropy as a metaphor. For example:

In human development and performance, entropy is somehow equated with limitations. It should be noted that if we go on to accept that people have limitations and a capacity for sin, then the natural pattern of human performance is not towards excellence but mediocrity. I say this because there are challenges, adversities, and even suffering, which are essential for healthy growth, although we don't normally seek or invite them. Overcoming these challenges, help us to see limitations as mere imaginations. Since entropy is very difficult to keep at bay, why must we continue to struggle against it in life? (Source)

I think that this paragraph has to be read as a somewhat confusing metaphor. It is not easy to characterize as a correct or incorrect understanding of entropy, but I suggest it is a bad metaphor. Entropy is not something that we can struggle against in the long term.

The Second Law and Creationism

This post is part of a series,Nonsense and the Second Law of Thermodynamics. The previous post is entitled Entropy and Information Theory.

Creationists and other people confused about the second law of thermodynamics  often bring up some variant of the idea that life is somehow a counter-example the second law of thermodynamics.  If entropy were disorder (which it is not), is it not obvious that life is highly ordered?

Therefore they seem to conclude that life is an example of decreasing entropy. The flaw in their thinking is not so much the confusion between disorder and entropy; the argument could be made with an accurate description of entropy. It would still be incorrect.

Partition Functions

This post is part of a series,Nonsense and the Second Law of Thermodynamics. The previous post is entitled Fluctuations.

In previous posts it was shown that entropy is related to the the number of ways that a system can arrange itself subject to constraints such as constant energy.

The previous post on fluctuations showed that for very large numbers that fluctuation from the most probable distribution, are insignificant.  Most of the distribution is contained within the square root of N of the most probable result.

Carbon Dioxide Poll

A recently closed poll on this blog posed the following question.  "The bending mode of carbon dioxide is:" Respondents were to respond with the best answer.  Here were the choices:

• A Hoax
• Not Dipole Allowed
• Degenerate
• A Blackbody
• The reason the sky is blue
• Even though I understand Global Warming, I don't know
• I don't know

I should point out that the answer to the question can be found in a post on this blog. The results of the poll are shown here:

Fluctuations

This post is part of a series,Nonsense and the Second Law of Thermodynamics The previous post is entitled Entropy and Statistical Dynamics.

The second law of thermodynamics works because of the statistics of very large numbers. Consider a bouncing ball: as it bounces, it dissipates heat and eventually does not bounce as high.  

Entropy and Statistical Thermodynamics

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Second Law and Swamp Coolers.

A previous post discusses the macroscopic thermodynamic definition of entropy, but there is another, statistical way of describing entropy.  Consider an isolated macroscopic system of interacting molecules.  Without knowing much about what is going on with the individual molecules, it is possible to measure macroscopic thermodynamic properties such as the pressure, the temperature etc.

                                                                                         (Figure Source)

Consider that the system is isolated; so that the total energy of the entire system of molecules is a constant.  Energy is free to move from one molecule to another, and each molecule has multiple electronic, vibrational, rotational, and translational energy states that it could be in.  There are many distinguishable ways that the system could be arranged to achieve the this energy.

The Second Law and Swamp Coolers

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Heat Can Be Transferred From a Cold Body to a Hot Body: The Air Conditioner.

When I was an undergraduate, I had a physical chemistry professor who claimed that air conditioners that were completely inside a room could not possibly work.  Opening the refrigerator door on a hot day will not make your house cooler.

The refrigerator gives off more heat than it transfers from inside itself; a refrigerator is actually heating the house.  If the door is left open, the refrigerator works harder to try to maintain a cool temperature in accordance with its thermostat setting.  As the refrigerator works harder, it releases more heat into the house.

My professor, however, was not correct.  It is possible to have a cooling unit that does more cooling than it releases heat to the environment.  The trick with indoor coolers is that the process by which they operate is not cyclic.

Heat Can Be Transferred From a Cold Body to a Hot Body: The Air Conditioner

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Hydrogen Economy.

As of 10/26/2010, a survey on this site shows that 25% (Final result 21%) of the respondents thus far think that the second law of thermodynamics says that heat cannot be transferred from a cold body to a hot body.

Not only are these people mistaken, but they are also ignoring their own common experience of the world.

It is possible to transfer heat from a cold reservoir to a hot reservoir!