Book excerpt: In Reactions, bestselling author Theodore Gray demonstrates, through stunning, never-before-seen images and illustrations, how molecules interact and change in ways that are essential to our existence. With Reactions, Theodore Gray completes the journey through the chemical world that began with the tour de force The Elements and continued with Molecules. In The Elements Gray showed us a never-before-seen photographic view of the 118 elements in the periodic table. In Molecules, he showed us how the elements combine to form the matter that makes up our world. At last, we've arrived at the final step in the chemical process. Reactions begins with a recap of elements and molecules and the goes on to explain the concepts that characterize a chemical reaction, including energy, entropy, and time. Gray introduces us to his favorite reactions, from those characterized by ignition and explosion, to photosynthesis, to "The Boring Chapter" in which he dives deep into reactions like paint drying, grass growing, and water boiling. Reactions is the spectacular finale of the three-act chemical drama that Gray has illustrated for us over the years in his engaging, entertaining, and inimitable way.