In a chemical reaction, the total mass of the products is equal to the total mass of the reactants.
This idea is called the conservation of mass.
Mass is conserved (kept the same) because no atoms are lost or made.
Chemical symbol equations must always be balanced to show this, i.e. there must be the same number of atoms of each element on both sides of the equation.
Due to conservation of mass, the sum of the relative formula masses of all the reactants is always equal to the sum of the relative formula masses of all the products.
