Chemists need to write equations. These equations tell us what happens in a chemical reaction. They come in two types.
A word equation-this just tells us the names othr reactants+products.
eg. Magnesium+Oxygen= Magnesium Oxide
A symbol equation which tells us the formulae of the substances and how much of each reactant is neede or product is formed.
Since the universe is governed by a law called the Conservation of Matter ( which ststes matter cammot be created nor destroyed) we have tobalence the equation. Add large numbers. (as above) to make sure there are the same number of each type of atom on both sides of the equal sign/arrow.