Final answer:
The mass at the beginning and end of a chemical reaction is equal, demonstrating the law of conservation of mass. This principle means the mass is neither created nor destroyed in a chemical reaction. A balanced chemical equation reflects this law with equal numbers of atoms for each element on both sides of the equation.
Step-by-step explanation:
Law of Conservation of Mass in Chemical Reactions
The mass at the start of a chemical reaction compares to the mass at the end of a chemical reaction by being equal, as per the law of conservation of mass. This fundamental principle holds that mass does not appear or disappear during a chemical reaction. Therefore, the total mass you have before a reaction will be the same as the total mass after the reaction, taking into account that all substances are accounted for and that the reaction is occurring in a closed system. When we add the masses of the reactants and compare them to the masses of the products, we notice that they are the same, indicating that mass is indeed conserved.
A balanced chemical equation always reflects this law by showing that the number of atoms for each element is the same on both sides of the equation. In terms of molar mass and moles, this relationship holds as well; the moles of reactants and products, when calculated using Avogadro's number, lead to the same total mass before and after a reaction. Consequently, in a chemical reaction, mass is neither created nor destroyed. This principle is a key aspect of stoichiometry, which involves the measurement of elements and the calculation of substances in a reaction.
It's important to note that small discrepancies like those seen in nuclear reactions, where a tiny fraction of mass may be converted to energy, don't apply to conventional chemical reactions and are outside the domain of classical chemistry.