Question

why does the total mass of reactants equal the total mass of products in a chemical reaction?
some of the reactant atoms are converted into energy.
the products are always in a different state of matter.
new atoms are created that are equal in mass to the reactants.
the atoms of the reactants are rearranged to form the products.

Explanation:

In a chemical reaction, atoms are neither created nor destroyed. The law of conservation of mass states that mass is conserved. Reactant atoms are just rearranged to form products. If atoms were converted to energy (violates mass - energy equivalence in normal chemical reactions, which is negligible for mass - conservation in chemistry), or new atoms created (contradicts atomic theory), or state of matter (state change doesn't affect mass conservation in this context) were the reasons, it would be incorrect. Rearrangement of atoms (which have mass) explains mass conservation.

Answer:

The atoms of the reactants are rearranged to form the products.