Kevin H. answered • 07/08/19
Former Chemical Engineering Professor
A lot of folks may describe entropy as "chaos" or "disorder". While those descriptors are not entirely inaccurate or wrong, they are best suited as a general guide.
When quantifying entropy, entropy is better defined as the number of states available. In other words, at the molecular level, how many configurations can the molecules and atoms have?
There are other definitions or ideas associated that definition, but I will focus on the implications associated with spontaneous processes.
Another quantity called Gibb's Free Energy is guided by entropy and energy (in the form of enthalpy). When Gibb's Free Energy decreases (due to lower energy and/or increasing entropy) a process will be spontaneous. In other words, the process does not require outside help (for example from an engine) to happen.
As such, to be able to predict if a process is spontaneous, you need to understand what happens to both energy AND entropy. For entropy, thinking about the states, possibilities, configurations, etc... enables you to predict if entropy will increase or decrease.
Example: imagine a can of soda (pop). When it is opened, it will eventually go flat. From an entropic perspective, while mixtures (CO2 and water) provide more configurations than pure substances, the CO2 can arrange themselves in infinitely more configurations when not bound by the liquid.
