Question

Which reaction illustrates conservation of mass?

A.
2 Cu + O2 → 2 CuO
B.
Fe + H2O → Fe3O4 + H2
C.
CH4 + Br2 → CBr4 + HBr

Answer 1

A, B, and C all illustrate conservation of mass because the number of atoms of each element is the same on both sides of the chemical equation, which means that the total mass of the reactants equals the total mass of the products. Therefore, the correct answer is all of the above.

Answer 2

A. 2 Cu + O2 → 2 CuO illustrates conservation of mass, as the total mass of the reactants (copper and oxygen) equals the total mass of the products (copper oxide). This is because in a chemical reaction, the total mass of the reactants must be equal to the total mass of the products.