Spontaneous physical changes are easy to predict. A dropped glass will fall to the ground once it is released. The reverse of a spontaneous event, like water flowing up a waterfall, will not occur except perhaps in the world of special effects for movies.

The probability of finding a highly ordered situation (e.g., a deck of cards in order) is much lower than a highly disordered one (in which the cards are random). Chemical reactions or events are driven toward spontaneity by the energetics of the process. Water will boil if heated to 100 °C at 1 atm.

Gas particles in one chamber will flow into an empty one (see figure: (a) is spontaneous while (b) is not).