Identify the reactants and products in the photosynthesis process. The reactants are carbon dioxide (CO2), water (H2O), and light energy. The products are glucose (C6H12O6) and oxygen (O2).
Write the unbalanced chemical equation for photosynthesis: CO2 + H2O + light energy β C6H12O6 + O2.
Count the number of each type of atom on both sides of the equation. Initially, you have 1 carbon, 2 hydrogens, and 3 oxygens on the reactant side, and 6 carbons, 12 hydrogens, and 8 oxygens on the product side.
Balance the carbon atoms by ensuring there are 6 carbon atoms on both sides. This requires 6 CO2 molecules on the reactant side: 6CO2 + H2O + light energy β C6H12O6 + O2.
Balance the hydrogen and oxygen atoms. You need 6 H2O molecules on the reactant side to balance the hydrogens, and this will also balance the oxygens when you have 6 O2 molecules on the product side: 6CO2 + 6H2O + light energy β C6H12O6 + 6O2.