Writing an equation
There is a standard method for writing an equation — and it is simple.
Three rules
- Writing reactants on the left and products on the right is the standard method.
- The direction the reaction runs in is shown by an arrow.
- When there are several substances on one side, the standard method is to put a (+) sign between them.
The shape of an equation
reactant + reactant → product + product
A single reaction may have several reactants and several products.
From words to formulae
The reactants and the products alike must be written using their chemical symbols and formulae.
The same reaction, two ways
magnesium + oxygen → magnesium oxide
Mg + O2 → MgO
The second is shorter, and it states the atom counts as well. But it is not yet complete — we find out why on the next page.
A common mistake
Oxygen gas must be written O2, not O — it exists as a diatomic molecule. The same goes for hydrogen, nitrogen and the halogens.