ENTROPY

Entropy is the tendency for matter to become disordered. Nature requires the input of energy to maintain an ordered state—a bedroom will become messy if not periodically cleaned; a car will eventually fall into disrepair if not regularly serviced. Entropy is an important force in chemistry. If other factors influencing a reaction are held equal, a chemical reaction will proceed spontaneously if the products have higher entropy (are more disordered) than the reactants. This law explains why ozone (O₃) gas can spontaneously decompose into molecular oxygen (O₂):

 2O_3(g) → 3O_2(g) 

This reaction occurs because the molecular order is diminished, resulting in a higher level of entropy.