A chemical reaction is a process that changes one set of chemical substances into another. These transformations involve breaking existing chemical bonds and forming new ones, resulting in a new substance with different properties than the starting materials. Chemical reactions occur constantly, from cooking food to the complex metabolic pathways that sustain life within biological systems. Understanding the distinct components that make up the reaction system helps explain how these changes occur.
Reactants The Starting Materials
The substances initially involved in a chemical reaction are known as the reactants, serving as the raw “ingredients” for the transformation. These starting materials must physically collide with sufficient energy and correct orientation to initiate the reaction. For a reaction to proceed, reactant molecules must acquire a minimum amount of energy, known as the activation energy. This energy is necessary to overcome the barrier and break the existing chemical bonds within the reactant molecules. The identity of the individual atoms within the reactants remains unchanged throughout the process. Only the electron arrangements and the connections between atoms are modified as the reaction progresses. In biological systems, reactants that specifically interact with enzymes are often referred to as substrates.
Products The Resulting Substances
Products are the new chemical substances formed as a result of the atomic rearrangement of the reactants. Once the activation energy barrier is overcome, the atoms from the starting materials reorganize and establish new chemical bonds, constituting the products. These resulting substances nearly always possess chemical and physical properties that are entirely different from the original reactants. For instance, the reaction between sodium metal and chlorine gas produces ordinary table salt, a product safe to consume despite its highly reactive and toxic starting components. The formation of products follows the Law of Conservation of Mass, which states that matter is neither created nor destroyed during a chemical reaction. The total mass of the reactants must be exactly equal to the total mass of the products, as every atom is simply reorganized into a new molecular structure.
Agents That Modify Reactions
Some substances influence the speed and efficiency of a chemical reaction without themselves being permanently consumed or altered in the process. The most common of these modifying agents are catalysts, which function by speeding up the reaction rate. A catalyst achieves this acceleration by providing an alternative reaction pathway that requires a lower activation energy than the uncatalyzed route. By lowering this energy barrier, a higher proportion of reactant molecules possess the energy needed to successfully react at any given moment.
In living organisms, specialized protein catalysts called enzymes are responsible for accelerating biochemical reactions, such as those involved in digestion, by many orders of magnitude. Conversely, certain substances known as inhibitors work to slow down or even prevent a reaction from occurring. Inhibitors often achieve their effect by raising the activation energy barrier or by interfering with the action of a catalyst. Neither catalysts nor inhibitors alter the fundamental identity of the reactants or the products, nor do they change the total amount of product that can ultimately be formed.