Mrs. johnson's science class perform an experiment. they combine two substances that react with lots of fizzing and bubbling. the class determines the mass of the substances before and after the experiment and find that the substances have less mass after the experiment. hannah wants to know why the experiment didn't obey the law of conservation of mass, but chris says it did. who is right and why? hannah is right because the class may have made an error in determining the mass of the substances. chris is correct because the reactants and products do not have to have the same mass, but they do have to weigh the same. hannah is right because the mass of the reactants was different than the mass of the products. chris is right because some of the mass of the reactants escaped as gas.