When substances transform into entirely new ones, a process known as a chemical reaction takes place. These reactions are fundamental to everything around us, from cooking food to the functioning of our bodies. They involve a change in the chemical identity of materials, leading to the formation of new substances with distinct properties. Understanding chemical reactions helps us comprehend how the world around us constantly changes.
The Basics: Reactants and Products
Every chemical reaction begins with starting materials called reactants. As the reaction proceeds, these reactants are converted into one or more different substances, known as products. For example, when wood burns, wood and oxygen are the reactants, while ash, smoke, and gases like carbon dioxide are the products.
A central principle in chemical reactions is the conservation of matter. This means that during any chemical reaction, atoms are neither created nor destroyed. Instead, the atoms present in the reactants are simply rearranged to form new combinations in the products. Their total number and type remain constant, only their bonding arrangements change.
Molecular Transformation: Breaking and Forming Bonds
The core of what happens to molecules during a chemical reaction involves the breaking and forming of chemical bonds. Within reactant molecules, existing bonds must first break apart. These bonds are the forces holding atoms together. Once broken, individual atoms or smaller molecular fragments become available for rearrangement.
These freed atoms or fragments then rearrange themselves into new combinations. They form new chemical bonds with different partners, creating entirely new molecular structures. This process of atoms unlinking and relinking in different ways forms new substances with distinct chemical properties. The atoms themselves remain unchanged; only their connections are altered, transforming reactants into products.
The Driving Force: Energy and Collisions
For chemical reactions to occur, molecules must interact. This often involves molecular collisions, where reactant molecules collide. Not every collision results in a chemical reaction, however. Collisions must occur with sufficient energy, known as activation energy, and with the correct orientation. This energy helps overcome the initial resistance to breaking existing chemical bonds.
Energy also plays a broader role in chemical transformations. Some reactions release energy into their surroundings, often as heat or light; these are called exothermic reactions. Other reactions require a continuous input of energy from the surroundings to proceed, absorbing heat; these are known as endothermic reactions. The balance of energy absorbed to break bonds and energy released when new bonds form determines whether a reaction is exothermic or endothermic.
Common Examples of Molecular Change
Everyday life offers numerous examples of molecules undergoing chemical changes. When iron rusts, it combines with oxygen in the air and water, transforming metallic iron into iron oxide, a reddish-brown substance. This involves the rearrangement of iron and oxygen atoms to form a new compound with different properties.
Another common example is the burning of wood, a combustion reaction. Complex organic molecules in wood react with oxygen from the air. This breaks down the wood’s large molecules, forming simpler molecules like carbon dioxide gas, water vapor, and solid ash.
A familiar kitchen reaction involves mixing baking soda (sodium bicarbonate) and vinegar (acetic acid). The molecules of these two substances react, forming new molecules, including carbon dioxide gas, water, and sodium acetate. The visible fizzing demonstrates the rapid production of carbon dioxide as new bonds are formed.