Respuesta :
Answer:
According to the law of conservation of mass, the masses of the products and reactants must be the same. Adding calcium to the product side is considered a mistake if it is not in the reactant side of a particular chemical equation because it is impossible to produce calcium from thin air (unless this is a nuclear reaction).
Explanation:
The law states that the total mass before a chemical reaction is the same as the total mass after a chemical reactionExothermic reactions do not require any activation energy.