The Second Law introduces the concept of Entropy —often misunderstood as "disorder," but Atkins prefers "spreading out" or "energy dispersal." He argues that the universe is driven by the tendency of energy to spread out as much as possible.

Atkins begins not with the first law, but with the "Zeroth." Historically, this law was formulated after the first and second laws, but scientists realized it was so fundamental that it had to come logically before them.