In chemical reactions, which of the following is always conserved?

In chemical reactions, mass is always conserved due to the law of conservation of mass. This law states that in a closed system, the total mass of the reactants must equal the total mass of the products; matter cannot be created or destroyed in an ordinary chemical reaction. Therefore, when substances undergo a chemical change, the atoms involved are rearranged to form new substances, but the overall mass remains constant.

The conservation of mass is crucial for understanding stoichiometry in chemistry, as it allows chemists to predict the amounts of products formed from given reactants and to balance chemical equations accurately. While volume, temperature, and pressure can change during a reaction depending on the conditions, the mass remains a constant factor throughout the process. Thus, mass conservation is a fundamental principle that underlies many aspects of chemistry and is essential for problem-solving and understanding reactions.