A student starts a reaction with two solids and measures the mass to be 100 grams. The reaction ends with one solid and a gas as the product. The mass of the product’s solid is 90 grams. Mass is conserved in a balanced chemical reaction. What happened? Why is the mass of the products not equal to that of the reactants?
In this scenario, the gas that is produced during the reaction is not accounted for in the initial mass measurement. Gases have mass, but since they are not contained or measured in this experiment, the total mass of the products (90g solid + gas) appears to be less than the initial mass of the reactants (100g solid).
To account for the total mass of the products, the mass of the gas must also be considered. If the mass of the gas is measured, the total mass of the products would be equal to the total mass of the reactants, thus upholding the principle of mass conservation in chemical reactions.