Wednesday, August 15, 2001

What is Thermodynamics?

The history of thermodynamics dates back to the nineteenth century. The field was developed to describe the operation of the steam engine, hence the title thermo (heat) - dynamics (power). In present day, the study of thermodynamics includes so much more than just the study of steam power. It is used to understand all sorts of thing including reactions in the cells in your body and mixtures of different liquids and gases.

Thermodynamics is based on three main laws. Like many scientific laws, these laws cannot be proven through math, but have not been proven wrong in nature. These laws are the same laws that scientists and engineers discovered when they were looking at steam and steam engines. They learned that the laws that steam obey in the engine works for all sorts of systems and chemicals.

The first law of thermodynamics states that the amount of energy in the universe does not change. When energy disappears in one form, it appears as another at that same moment. To understand this better we will look at the two main types of energy, kinetic and potential. Kinetic is the energy of motion and potential is stored energy. A car at the top of a big hill is full of potential energy, because of the difference in height at the top and bottom of the hill. As the car goes down the hill, potential energy is released in the form of kinetic energy. Potential energy can also be stored in chemical bonds. Bonds are what keep molecules together, like hydrogen and oxygen in water. When a molecule is made from atoms, energy is used to create the bonds. A good example of chemical bonds releasing energy is a campfire. The chemical bonds in the wood break producing heat and light. Sometimes a campfire crackles; this is another way energy is expressed, sound. Energy can be released from bonds as heat, light and sound.

The second law of thermodynamics says that the amount of energy a system puts out can not be greater than the amount of energy put into the system, or simply, you can not get something for free. This rule also tells us that nothing is perfect. We can look at a car engine as an example. All of the energy stored in the chemical bonds of the gas is not converted completely to energy to drive your car. The law tells us that the energy in a system cannot be made totally into work, that no engine is perfect. This is why a perpetual motion machine cannot be made. A perpetual motion machine is an ideal, fantasy machine that the operator can start moving and run forever without adding any energy once it has started. Here is a web page that discusses the history of the perpetual motion machine:

The third law of thermodynamics states that all things will become less and less organized. Scientists and engineers have a term called entropy. Entropy helps relate how chaotic or disorganized a system is. At the coldest temperature, absolute zero (-270 degrees Celsius), the absolute value of entropy is zero. An example of why this law is thought to be true is the constant expansion of the universe. The entropy at the time I wrote this article is less then the entropy when you read this article!

The laws of thermodynamics are universal for everything and have yet to be proven wrong!