text: chemistry question...in reactions, do the reactants weigh more, less, or the same as the product? take for example this reaction:  2nacl + 2h2o --> 2naoh + cl2 + h2  do the reactants  weigh more because cl2 and h2 are gases weigh the same as the products weigh more than the products because the reaction isn't perfect their is no loss or gain of atoms, once you balance the equation, so the products weight the same as the reactants.  the fact that h2 and cl2 are gases doesn't affect the weight of the compounds used, as long as the reaction is done in a closed container and you don't lose any.