How do we interpret a chemical equation ?
The equation of a chemical reaction makes possible the quantitative treatment of the reactants consumed and the products formed at the microscopic scale (number of atoms , ions and molecules ) and the macroscopic scale (number of moles ) . The equation of the formation of water from hydrogen and oxygen is :
2H2(g)+O2(g) –> 2H2O(g)
At the microscopic scale , this equation shows that two molecules of hydrogen react with one molecule of oxygen to give two molecules of water .
At the macroscopic scale , this equation shows that two moles of hydrogen react with one mole of oxygen to yield two moles of water .