Second Law of Thermodynamics

Yesterday we looked at the First Law of Thermodynamics. I said that in my 41 years of teaching high school physics, the hardest part was getting students to see how the subject applied to their lives. If they understood that life is not possible without the laws of thermodynamics, they would realize the importance of the topic and find it easier to understand. As with the First Law, the Second Law of Thermodynamics is essential to our existence.

THE SECOND LAW OF THERMODYNAMICS: In Any Energy Conversion, Some Energy is Lost in the Form of Heat, Which Cannot be Recovered as Useful Energy.

This statement of the Second Law is known as the Clausius statement. What it describes is heat death. In any closed system, things tend to move toward a condition of disorder. We call that disorder “entropy.” The law does not say that energy is destroyed, because that would violate the First Law. It merely states that there is always some energy that cannot be recovered in any physical process. Things always move toward a condition of disorder.

To help students understand the Second Law, I would have a student put a spoon on the desk. While I was talking to the class, one end of the spoon would get hot and start to smoke. I would deny it was hot by picking it up at the other end and then putting it back right where I found it. There it would continue to get hotter and hotter on one end. The class would go ballistic, and I would ask them, “What’s the problem?” After a barrage of nutty answers (it’s haunted, it’s an illusion, etc.), I would point out that they had faith in the Second Law of Thermodynamics.

Common sense tells them that order (the cold end) cannot exist at the same time as disorder (the hot end). I had an induction coil under the desk-top that was heating the spoon, but we all know that one end cannot remain hot, and the other end cold. Gases diffuse, things fall apart, and people get old because of the Second Law of Thermodynamics.

My favorite example is a teenager’s room, which becomes more and more disordered with time in conformance to the Second Law. It is essential to understand that all of these examples assume that no one is improving the order from the outside. If Mother comes along and makes you clean up your room, then the room is no longer a closed system. Organizing energy is added from the outside. The Second Law applies to systems in which no external organizing energy is added to the system. The induction coil made the spoon an open system.

The Second Law of Thermodynamics has enormous implications for cosmology. It says that, like us, all stars and all galaxies will eventually die. The cosmos is not eternal. There had to be a specific point at which the cosmos had no unusable energy. At that point, there was no entropy. The biblical statement that there was a beginning is strongly attested to by the Second Law of Thermodynamics.

We must point out that it is incorrect to apply the Second Law to planet Earth or to anything on Earth. Some creationists have attempted to attack evolution based on the Second Law, but Earth is not a closed system. Photosynthesis works because the Sun is adding energy to the Earth. Biological systems can have energy added to them by any number of methods such as light, radiation, heat, or thermal vents. The added energy improves order, reducing entropy. Although the Second Law verifies many biblical statements, it is not a tool to attack evolution.

Tomorrow we will examine the Third Law of Thermodynamics.

— John N. Clayton © 2020

Note: Laws are quoted from Physics, Principles and Problems, Glencoe Publications of Macmillan/McGraw Hill, PO Box 508, Columbus, Ohio 43216, pages 256-259.