Final answer:
The mass of the products of a chemical reaction in a closed system must be equal to the mass of reactants according to the law of conservation of mass, which in this case is 35 grams.
Step-by-step explanation:
According to the law of conservation of mass, the mass of products in a chemical reaction must be equal to the mass of reactants in a closed system. Therefore, if the mass of the reactants was measured at 35 grams before the reaction, the mass of the products after the reaction must also be 35 grams. This law indicates that matter, in the form of atoms and molecules, cannot be created or destroyed in a chemical reaction; it can only be transformed from one form to another.
An example of the law of conservation of mass can be observed in the simple synthesis of water from hydrogen and oxygen gases. If we start with 2 grams of hydrogen and 16 grams of oxygen, after the reaction to form water, we will still have a total of 18 grams of water, demonstrating that mass is conserved.