A chemical reaction is a fundamental process where substances change into entirely new ones. It involves a transformation at the molecular level, resulting in products with properties distinct from the starting materials.
Molecules Transform
During a chemical reaction, the original substances, known as reactants, undergo a change. Their constituent molecules are effectively taken apart, and their atoms then rearrange to construct entirely different molecules, which are the products. For instance, hydrogen and oxygen gases, both invisible, can react to form liquid water, a substance with vastly different characteristics.
Imagine molecules as intricate structures built from Lego bricks. In a chemical reaction, these existing Lego structures (reactants) are disassembled into their individual bricks (atoms). These same bricks are then reassembled into new and different Lego structures (products). The type and number of bricks remain the same, but their arrangement creates something new.
The Role of Chemical Bonds
The mechanism behind this molecular transformation lies in chemical bonds. Atoms within molecules are held together by these bonds, which are essentially forces of attraction. For reactants to become products, the existing chemical bonds within the reactant molecules must first break. This breaking of bonds allows the atoms to become free to rearrange.
Once the old bonds are broken, new chemical bonds form between the rearranged atoms to create the product molecules. This process of bond breaking and bond formation is at the core of all chemical changes.
Energy’s Crucial Role
All chemical reactions involve changes in energy. Energy is always required to break the existing chemical bonds in the reactant molecules. Conversely, when new chemical bonds form to create the product molecules, energy is released.
If a reaction releases more energy when new bonds form than it absorbed to break old bonds, it is an exothermic reaction, often felt as heat or light being given off. Examples include burning. If, however, more energy is absorbed to break bonds than is released when new ones form, it is an endothermic reaction, and the system typically absorbs heat from its surroundings, often feeling cold.
Atoms Are Conserved
A fundamental principle governing all chemical reactions is the conservation of atoms. While molecules are transformed and chemical bonds are broken and formed, the individual atoms themselves are neither created nor destroyed. They simply rearrange into new combinations.
Consider the Lego analogy again: when you take apart old structures and build new ones, you still have the same number and types of Lego bricks you started with. Similarly, in a chemical reaction, the atoms are merely shuffled and reassembled. This concept is encapsulated in the law of conservation of mass, which states that the total mass of the reactants before a reaction equals the total mass of the products after the reaction.