Chemical reactions are reversible and may reach a dynamic equilibrium. The direction of reversible reactions can be altered by changing the reaction conditions. Ammonia is made by the Haber process.
Many chemical reactions are reversible reactions. This means that the products can be changed back into the original reactants. This is not obvious when a reaction 'goes to completion', where very little or no reactants are left.
Examples of reactions that go to completion are:
It is more obvious in reactions that do not go to completion that the reaction is reversible. This is the case when the reaction mixture contains both reactants and products.