This has often been summarized as, 'You can't unscramble an egg.' According to Wolfram, Boltzmann realized around 1876 that the reason for this is that there must be many more disordered states for a system than there are ordered states therefore random interactions will inevitably lead to greater disorder. However, the warm gas will never spontaneously separate itself into hot and cold gas, meaning that the process of mixing hot and cold gases is irreversible. The result of this is that when hot gas and cold gas are placed together in a container, you eventually end up with warm gas, according to Georgia State University (opens in new tab). With large quantities of gas, the speeds of individual molecules tend over time to form a normal or Gaussian distribution, sometimes depicted as a 'bell curve,' around the average speed. This approach also led to the conclusion that while collisions between individual molecules are completely reversible, i.e., they work the same when played forward or backward, that's not the case for a large quantity of gas. The process taken as a whole results in a net increase in disorder. Crystals are more orderly than salt molecules in solution however, vaporized water is much more disorderly than liquid water. In another example, crystals can form from a salt solution as the water is evaporated. Even when order is increased in a specific location, for example by the self-assembly of molecules to form a living organism, when you take the entire system including the environment into account, there is always a net increase in entropy. Mitra explained that all processes result in an increase in entropy. 'At a very microscopic level, it simply says that if you have a system that is isolated, any natural process in that system progresses in the direction of increasing disorder, or entropy, of the system.' 'There are a number of ways to state the Second Law,' Mitra told Live Science. Saibal Mitra, a professor of physics at Missouri State University, finds the Second Law to be the most interesting of the four laws of thermodynamics.

Entropy examples