conservation of mass – the law that states that no atoms are lost or made during a chemical reaction

To remember the meaning of conservation of mass, use the following mnemonic:

The zoo once focused on the conservation of these massive (conservation of mass) creatures, but now they are all dead. None will ever be lost or gained again.

Conservation of mass is a fundamental principle in chemistry which states mass cannot be created or destroyed during a chemical reaction. This means that the total mass of all the reactants at the start of the reaction must equal the total mass of all the product at the end of the reaction. For example, if you react 10 grams of magnesium with 6.58 grams of oxygen, the mass of magnesium oxide will be 16.58 grams.

In a closed system, no atoms are lost or gained during a reaction - they are simply rearranged to form new substances. This is why chemical equations must be balanced, as they need to show the same number of each type of atom on both sides of the equation to reflect this conservation of mass. Sometimes it may appear that mass has been gained or lost, such as when gas escapes from a container or when gas from the air reacts to a substance, but in reality the total mass of the material remains consistent.