text: given the following unbalanced chemical equation ch4+o2=co2 +h2o? what is the chemical formula of the limiting reagent or reactant if 35 grams ch4 are mixed with and react with 53 grams o2? well, i won't do it for you - but here is how to do it.  you have one c on each side so that is good.  but you have 4 hs on the left side so you need 2 h2os on the right to balance the hs.  now you have 4 os on the right, so you need to make your 2 o2s on the left to balance the oxygen.  ch4 + 2 o2   =   co2 + 2 h2o  now - using the atomic weights of h=1, c=12, o=16, you get molecular weights for methane = 16 and 02 = 32.  convert the weights of menthane and o2 into moles using the molecular wieghts - whichever is the smaller # of moles is the limiting reagent - meaning that the reaction will stop when this reagent has been used up.