A chemical reaction is a fundamental process where substances transform into new and different substances. This transformation involves changes at the atomic and molecular level, leading to the creation of materials with distinct properties from the starting substances. This article explains what happens to atoms during these chemical transformations.
Rearrangement of Atoms
During a chemical reaction, atoms themselves do not change into different types of atoms. Instead, the process involves the breaking of existing chemical bonds within the initial substances and the formation of new bonds to create new substances. The original substances are known as reactants, and the newly formed substances are called products.
Imagine atoms as building blocks. In a chemical reaction, the “linked” blocks (molecules) are first disassembled. These individual blocks (atoms) are then “relinked” in different combinations to form new structures (new molecules). This rearrangement of atoms is what fundamentally defines a chemical change, resulting in products with different characteristics from the reactants.
The identities of the atoms are preserved throughout this process; for instance, a carbon atom remains a carbon atom, and an oxygen atom remains an oxygen atom. What changes is how these atoms are connected to each other.
Conservation of Mass and Atoms
A fundamental principle governing chemical reactions is the Law of Conservation of Mass, which states that matter is neither created nor destroyed. This means the total mass of the reactants before a reaction is equal to the total mass of the products after the reaction. This principle holds because the atoms themselves are conserved.
The types and quantities of atoms present before a reaction are exactly the same after the reaction; they are simply reorganized. For example, if you start with a certain number of carbon atoms, hydrogen atoms, and oxygen atoms, you will have the same number of each type of atom in the products. No atoms disappear, appear, or transform into other elements during a chemical reaction.
This conservation of atoms is why chemical equations must be balanced. A balanced chemical equation shows the same number of each type of atom on both the reactant and product sides, ensuring that the law of conservation of mass is upheld.
Energy Changes in Reactions
Chemical reactions involve changes in energy, as energy is either absorbed from or released into the surroundings. Energy is required to break the existing chemical bonds in the reactant molecules. This process, where energy is taken in, is termed endothermic.
Conversely, energy is released when new chemical bonds are formed to create the product molecules. This energy-releasing process is known as exothermic. The net energy change of a reaction, determined by the balance between energy absorbed for bond breaking and energy released during bond forming, dictates whether the overall reaction will absorb heat (endothermic) or release heat (exothermic). For instance, burning a fuel is an exothermic reaction that releases heat, while the process inside a cold pack is an endothermic reaction that absorbs heat.
Before a reaction can proceed, an initial energy input, known as activation energy, is often necessary. This is the minimum energy required to initiate the reaction. Even for reactions that ultimately release energy, this initial energy barrier must be overcome to break the first set of bonds and allow the atomic rearrangement to begin.