16-17) The Three Major Types of Chemical Reactions, Oxidation and Irreversible Reactions.

A Chemical Reaction occurs whenever chemical bonds are formed, rearranged, or broken. The three major types of chemical reactions are synthesis, decomposition, and exchange.
-A SYNTHESIS REACTION always involves bond formation. Synthesis reactions are the basis of constructive (or anabolic) activities in the cells. A synthesis reaction is written like this: A+B➡️AB
-A DECOMPOSITION REACTION occurs when a molecule is broken down into smaller molecules or its constituent atoms. Decomposition reactions are reverse synthesis reactions; bonds are broken. Decomposition reactions underlie all degradative (or catabolic) processes that occur in body cells. A decomposition reaction is written like this: AB➡️A+B
-An EXCHANGE or DISPLACEMENT REACTION involves both synthesis and decomposition bonds are both made and broken. In exchange reactions, parts of the reactant molecules change partners, producing different product molecules. An exchange reaction is written like this: AB+C➡️AC+B or AB+CD➡️AD+CB
-An OXIDATION REDUCTION REACTION (redox reactions) are the basis of decomposition reactions in which food fuels are catabolized for energy (ATP is produced). Oxidation reduction reactions are also special types of exchange reactions because electrons are exchanged between the reactants. The reactant losing the electrons is referred to as the electron donor and it is said to be oxidized. The reactant taking up the transferred electrons is called the electron acceptor and is said to become reduced. Oxidation reactions occur when ionic compounds are formed. Not all oxidation reduction reactions involve a complete transfer of electrons.

Sometimes chemical reactions in the body are reversible. This is true in many biological reactions. Chemical reactions that release energy when going in one direction will not go in the opposite direction unless energy is put back into the system. For example: when cells break down glucose via the reactions of cellular respiration to yield carbon dioxide and water, some of the energy released is trapped in the bonds of ATP. Because the cells need ATP's energy for various funcations, this particular reaction is never reversed in our cells.