In a laboratory investigation, a student mixes a solution containing 20.8 g of barium chloride (BaCl2\text{BaCl}_2BaCl2) with a solution containing 14.2 g of sodium sulfate (Na2SO4\text{Na}_2\text{SO}_4Na2SO4). A white precipitate of barium sulfate (BaSO4\text{BaSO}_4BaSO4) and a solution of sodium chloride (NaCl\text{NaCl}NaCl) are formed:
BaCl2(aq)+Na2SO4(aq)→BaSO4(s)+2NaCl(aq) \text{BaCl}_2(aq) + \text{Na}_2\text{SO}_4(aq) \rightarrow \text{BaSO}_4(s) + 2\text{NaCl}(aq) BaCl2(aq)+Na2SO4(aq)→BaSO4(s)+2NaCl(aq)The combined mass of the reactants before mixing is 35.0 g. After the reaction is complete, the total mass of the resulting mixture is also found to be exactly 35.0 g.
Explain, in terms of atoms, why the total mass of the products must be exactly equal to the total mass of the reactants.
