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.

Site Redesign

Frequent visitors may have noticed that I've redesigned the site. An unfortunate consequence is that two of the polls were lost; I've recreated them but lost the votes to date.

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.

Converting Units of Temperature

In the course of writing articles for this blog, on occasion I write a post on the conversion of units.  Units can be confusing for some, and if I can add some clarity, I think it is worth doing.  This post addresses conversion between units of temperature. 

The most common temperature conversion that one wants to do is to convert degrees Celsius to degrees Fahrenheit or vice versa.  I hope to explain how to do this conversion in such a way that one need not memorize a formula, even to get the exact answer.

First, it is worthwhile to mention a quick and dirty approximation that almost anyone can do in his or her head.  It is not exact, but it is useful, if you are traveling to a country that uses a scale that is different than the one you use to think about ambient temperatures.

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.