He then came up with a term he called the “mean length of the path” which was “how far on an average can the molecule move, before its center of gravity comes into the sphere of action of another molecule. In other words, in cigar smoke (or in any gas) there are a ridiculous number of molecules moving in all directions but they don’t get very far before bouncing off of another molecule and changing direction, so that even though the individual gas molecules are moving very quickly, the gas itself diffuses slowly. Even with these limitations, Clausius found that molecules move at very fast speeds.įor example, Clausius found that hydrogen gas at 0 Celsius should move at slightly more than5 times the speed of sound! After reading Clausius another scientist published an objection, if gas molecules are really moving so fast how come cigar smoke doesn’t fill the room faster than the speed of sound?Ĭlausius felt like this was an interesting objection (writing he “rejoice at the discussion ”), but instead of invalidating his theories Clausius decided that it would all work out if the molecules are moving very fast but not very far. In this paper Clausius became the first person to include rotational and vibrational motion of molecules as well as linear motion. Now I want to take a moment to talk about the history of probability in thermodynamics and I am going to also start with… ready for it… a German man named Rudolf Clausius! In 1857, three years after Clausius’s first paper introducing the “equivalence value”,Ĭlausius wrote a paper on what the temperature meant about the motion of molecules. Finally, in 1865, Clausius renamed the “equivalence value” the entropy and gave it the letter S and defined the second law of thermodynamics to be the entropy of the universe can only increase, which is a modern definition. In other words, the “equivalence value” (entropy) of a closed system can only increase. He also found that any decrease in “equivalence function” on one object would necessitate an increase of equal or greater value in other objects. In 1854, a German scientist named Rudolf Clausius noted that absorbing less heat at a lower temperature was equivalent to absorbing more heat at a higher temperature so he called the heat over the temperature the “equivalence value” (he would later call the equivalence value the entropy).īy 1862, Clausius found that an increase of the equivalence values of a single process would increase the separation of the molecules or disorganize their relationship. I would like to start with the origin of the idea of entropy. Table of Contents Entropy by Rudolf Clausius The Relationship of Statistics and Entropy Max Planck Planck’s Equation Boltzmann’s Famous Equation References

Boltzmann entropy