Chemical reactions are occurring all around us. When we turn on the stove, gas reacts with oxygen to produce heat. When oxygen reacts with iron and water, iron hydorixde, or rust, forms. Plants take in oxygen and sunlight to form water and glucose in a chemical reaction called photosynthesis. Among the many types of chemical reactions, one of the most important type is oxidation-reduction reactions, or simply redox reactions. The defining characteristic of redox reactions is that one or more electrons are transferred during the reaction. The addition or removal of electrons to or from an element changes the chemical properties of the element, and allows it to form new bonds with other elements.