Question

Which of the following equations violates the law of conservation of mass?

Answer 1

Answer: Option (D) is the correct answer.

Explanation:

Law of conservation of mass states that energy can neither be created nor it can be destroyed. It can only be transformed from one form to another.

Therefore, in a chemical reaction an equation can only be balanced if the number of reactants equal the number of products because energy required for reactants is utilized in the formation of the products.

For example, $2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}$ is a balanced equation because the number of reactant atoms equal the number of product atoms.

Thus, we can conclude that out of the given options, $3Ca + 2Cr(NO3)_3 \rightarrow 3Ca(NO3)_{3} + 2Cr$ equations violates the law of conservation of mass because number of reactant atoms does not equal the number of product atoms.

Answer 2

D is the answer.
On the left, there are 3 atoms of Ca, 2 atoms of Cr, 6 atoms of N, and 18 atoms of O.
On the right, there are 3 atoms of Ca, 9 atoms of N, 27 atoms of O, and 2 atoms of Cr.