By David Dunning, updated Aug 30, 2022
The fundamental principle of chemistry, the Law of Conservation of Matter, states that matter cannot be created or destroyed in a closed system. In a typical chemical reaction, the total mass of the reactants equals the total mass of the products. This means the amount of matter before and after the reaction remains constant.
Consider the reaction of hydrogen gas (H₂) with oxygen gas (O₂) to form water (H₂O). One mole of water contains two moles of hydrogen and one mole of oxygen. In mass terms, 2.02 g of hydrogen reacts with 16 g of oxygen to produce 18.02 g of water, perfectly illustrating the conservation of mass.
The law also allows chemists to deduce the empirical formula of an unknown compound. By measuring the mass of each element in a sample and reducing the resulting ratios to their simplest whole‑number form, the empirical formula can be determined.
Atom economy refers to the fraction of reactant atoms that end up in the desired product. Reactions with high atom economy convert most of the starting material into useful products, generating less waste. Such processes are central to green chemistry initiatives aimed at reducing environmental impact.
Understanding these principles is essential for chemists, engineers, and anyone working with chemical processes.
