With the book Reactions, bestselling author Theodore Gray continues his journey into the molecular and chemical world that began with The Elements and continued with Molecules. In The Elements, Gray offered us a unique, captivating photographic view of the 118 elements of the periodic table. In Molecules, with the same exceptional photographic ability and beautifully designed graphics, he presented us with how the elements combine to form the substance that makes up our universe, from salt to oxygen and the vast variety of colors and scents that surround us. In Reactions, Gray once again utilizes his photography and storytelling to show how molecular interactions are vital to our existence. The book begins with a brief review of elements and molecules and then explains key concepts that define a chemical reaction, including Energy, Entropy, and Time. Organization by reaction type includes Combustion, Photosynthesis, Respiration, Oxidation, and Fermentation. A special section dedicated to chemical cycles includes the Carbon Cycle, the Iron Cycle, and the Lime Cycle.