now that we understand how to notate chemical equations we need to know how to balance them this involves finding the correct coefficients for each substance involved in the reaction we need to find these coefficients in order to accurately describe what is occurring in the reaction because the chemistry will strictly obey these ratios for example in the combustion of methane we can see that the coefficients are 1 2 1 and 2 because these are the number of molecules we will need of each substance in order to ensure that there are the same number of atoms of each element on each side this is important because chemistry obeys conservation of mass this means that in a chemical reaction atoms are not created or destroyed they simply rearrange their combinations so the atoms that are present on the reactant side must all be accounted for on the product side counting up the atoms on the reactants side of this reaction there is one carbon atom four hydrogen atoms and two oxygen atoms since this is also the case for the products this equation is balanced let's look at an unbalanced equation so we can practice electrolysis of water can produce hydrogen gas and oxygen gas as is illustrated by this equation but we need to know the ratios of each substance involved so let's balance these elements one at a time there are two hydrogen atoms on the left and two on the right so far so good but for oxygen there is one on the left and two on the right so we can balance that by placing a two in front of water because two water molecules will give us two oxygen atoms on the left but now there are four hydrogen atoms on the left as well so we will need to put a two in front of hydrogen to get four hydrogen atoms on the right now this equation is balanced there are the same number of each type of atom on each side let's try one more for this one nitrogen looks good as it is but for oxygen we have a 2 to 5 ratio let's put a 5 here and a 2 here so that there are 10 oxygen atoms on each side let's check on nitrogen again nitrogen became unbalanced when we added the 2 on the right side of the equation now there are 4 on the product side so we need to put a 2 here to get 4 on the reactant side too and now we know how to balance chemical equations