In a chemical reaction, what is the mass of the products?
The mass of the products is the same as the mass of the reactants in any chemical reaction.
Mass is conserved in every chemical reaction. If I start with 10 g of reactant, from all sources, I will finish with (at most!) 10 g of product (and of course most of the time I won't even get that due to handling losses). Every chemical reaction is evidence of this condition.
Are masses conserved in nuclear reactions?