Entropy isn't a measure of chaos, really, but rather a measure of how energy is statistically distributed. There is a natural tendency for energy to be "spread out", which we call maximizing entropy. (Colloquially we may call this "chaos" or "disorder", but that's not particularly scientific.) In a chemical system there is a kind of force that directs the system toward a state of maximum distribution (spatial, if it's simple to think of it that way) of energy. However a change in entropy doesn't necessarily mean the energy of the system has changed, just the way it is distributed in the system. For example, an expanding ideal gas that loses or gains no energy will still exhibit a significant gain in entropy, because the system's energy gets spread out over a larger area.