Chemical Quantities: Conservation of Mass

Law of Conservation of Mass states that the total mass of reactants in a chemical reaction is always equal to the total mass of the products.
This means that no atoms are lost or made during a chemical reaction, and atoms are simply rearranged to form new substances.
With this understanding, we can balance chemical equations, which requires having equal numbers of each type of atom on both sides of the equation.
Molar calculations can often be used to calculate the mass of reactants or products in a chemical reaction. One mole of a substance is always equal to its relative formula mass in grammes.
The Avogadro constant (6.02 x 10^23) is the number of atoms, molecules or ions in one mole of a substance.
In chemical reactions, mass is conserved when a system is closed, meaning nothing enters or leaves the reaction system.
In cases where gas is involved in a reaction, the mass might seem to change if the system is not closed since the gas can escape.
In practical experimentation, such as when a metal reacts with an acid to produce a salt and hydrogen gas, it’s essential to ensure the system is closed to observe mass conservation.
Relative atomic mass allows us to calculate the mass of the reactants and the products in a chemical reaction. It is an average value, considering the isotopes of an element and their relative abundance.
Reactions that seem to involve a mass change, like when a metal reacts with oxygen to form a metal oxide, still obey the law of conservation of mass, but the mass of the oxygen from the air is often not accounted for in initial mass measurements.
Percent yield is a concept that measures the efficiency of a chemical reaction, comparing the actual yield of a reaction to the maximum possible yield, based on stoicheiometry. This is essential in industrial chemistry to maximise product and minimise waste.