The principle that the number of atoms stays the same during a chemical reaction is known as the law of conservation of mass, or more specifically, the law of conservation of matter. This law states that in a closed system, mass cannot be created or destroyed; it can only be rearranged or transformed.
During a chemical reaction, atoms are rearranged to form new chemical compounds. However, the total number of atoms before and after the reaction remains constant. This is because chemical reactions involve the breaking and forming of chemical bonds between atoms, but the actual atoms themselves are not created or destroyed in the process.
To illustrate this, let's consider a simple example: the reaction between hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O). Before the reaction, we have two hydrogen molecules (H₂) and one oxygen molecule (O₂):
2H₂ + O₂
After the reaction, the atoms are rearranged to form two water molecules:
2H₂O
In this example, we started with a total of four hydrogen atoms (2 × 2) and two oxygen atoms. After the reaction, we still have a total of four hydrogen atoms (2 × 2) and two oxygen atoms. The number of atoms remains the same.
This conservation of atoms holds true for all chemical reactions, as long as the reaction takes place in a closed system where no atoms are gained or lost from outside sources. It is a fundamental principle in chemistry and provides a basis for balancing chemical equations and understanding the stoichiometry of reactions.