A chemical reaction is a process that involves the transformation of one or more substances, known as reactants, into new substances, called products. During a chemical reaction, chemical bonds between atoms are broken and new bonds are formed to create different molecules or compounds.

Chemical reactions occur when reactant molecules collide with sufficient energy and proper orientation. This collision causes the rearrangement of atoms, leading to the formation of new chemical compounds.

Chemical reactions can be represented using chemical equations, which provide a concise way to describe the reactants and products involved. The reactants are written on the left side of the equation, and the products are written on the right side, separated by an arrow. The arrow indicates the direction of the reaction.

For example, the chemical reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O) can be represented by the following balanced chemical equation:

2H2 + O2 → 2H2O

This equation shows that two molecules of hydrogen gas react with one molecule of oxygen gas to produce two molecules of water.

Chemical reactions can be classified into different types, including synthesis or combination reactions, decomposition reactions, displacement reactions, redox reactions, and many more. These reactions play a fundamental role in various natural and industrial processes, including biological reactions, combustion, digestion, and the production of materials and energy.