Describe what a chemical reaction is, in terms of the substances involved and the atoms that make them up.

Understanding Chemical Reactions

A chemical reaction is a process in which substances, known as reactants, undergo a transformation to form new substances called products. This transformation involves the breaking and forming of chemical bonds between atoms.

1. Substances Involved:

   • Reactants: These are the initial substances that undergo change during a reaction. For example, in the combustion of methane (CH₄), the reactants are methane and oxygen (O₂).
   • Products: These are the new substances formed as a result of the chemical reaction. In the case of methane combustion, the products are carbon dioxide (CO₂) and water (H₂O).

2. Atoms and Their Rearrangement:

   • Atoms are the basic units of matter and consist of protons, neutrons, and electrons. During a chemical reaction, the arrangement of atoms within the reactants changes to create the products.
   • The bonds that hold atoms together are broken in the reactants, and new bonds are formed to create the products. This can involve the transfer of electrons, which results in the formation of ions or molecules with different structures.

3. Conservation of Mass:

   • An important principle in chemical reactions is the conservation of mass, which states that the total mass of the reactants must equal the total mass of the products. This is because atoms are neither created nor destroyed in a chemical reaction; they are merely rearranged.

In summary, a chemical reaction is defined by the transformation of reactants into products through the rearrangement of atoms and the breaking and forming of chemical bonds.