What is the change in entropy when a gas expands or gases mix or liquids mix?
In all of the preceding examination of entropy, we have been considering — essentially — the change in entropy when energy is transferred from the surroundings to a system, and we found that the traditional entropy equation of q/T aids in understanding why things happen: the less it is hindered, the more the q ‘motional energy’ tends to spread out or disperse. But what does entropy have to do with spontaneous events where there isn’t any transfer of energy from the surroundings? Why do gas molecules spread out into a vacuum? That doesn’t take any energy flowing from the surroundings. Why do gases spontaneously mix and liquids that are somewhat like each other mix easily without any help? Why do so many chemicals dissolve in water? By now, you can hardly help guessing correctly! All these events must have something to do with energy dispersing of spreading out. The only difference between them and what we have talked about before is that they all involve a system’s initial energy spread
