The mass of the product would be equal to the sum of the masses of the reactants given there is only one product. The mass would be 47.0 g XY2 product. This is in accordance with the law of conservation of mass where it states that mass cannot be created or destroyed. So, in a certain process, what mass goes in should be equal to the mass that goes out whether a reaction or a physical process is happening in the process. This is also applicable for chemical reactions. The mass of the product should be equal to the mass of the reactants.