Pity the poor thermodynamics student of the future. As difficult as thermo can be for budding engineers to learn, it is going to get a lot more complicated if a recently published theory is true. Theoretical physicist Lorenzo Maccone recently proposed that entropy can, in fact, decrease under special circumstances. Here is part of the explanation:
"The key to entropy decrease in the first place is a correlation between the observer and the phenomenon in question. As Maccone explains, when an interaction occurs between an observer and an observed phenomenon that decreases the entropy of the correlated observer-observed system, the interaction must also reduce their quantum mutual information. When this information is destroyed, the observer's memory is destroyed along with it. "
Well, that certainly clears things up.
You can wade through more of this explanation here:
http://www.physorg.com/news170586562.html
One thing to keep in mind through all this is that the concept of entropy was introduced by mathematician who was trying to express the second law of thermodynamics in an equation. He introduced the idea of entropy simply to get the equation to work out.