Question

If you were to measure the mass of magnesium and hydrochloric acid before combining them in the test tube, how would that mass compare to the mass of reactants left in the test tube after the reaction? Explain your answer and how it corresponds to the law of conservation of mass.

Answer 1

The balanced chemical reaction for the system given is as follows:

2Mg + 2HCl = 2MgCl + H2

The mole ratio of the reactants is one is to one which means with a given amount of magnesium requires the same amount of hydrochloric acid to have a complete reaction. If supplied exactly, then after the reaction, all of the reactants are consumed and formed into the products.

Answer 2

Answer:

The mass of left over reactants after the reaction will be less than that of the mass of Magnesium and hydrochloric acid before the reaction as the reactants react to form the products.

Explanation:

The balanced chemical equation representing the reaction of Mg and HCl:

$Mg (s) + 2 HCl (aq) --> MgCl_{2}(aq)+H_{2}(g)$

As per the Law of conservation of mass, the total mass of reactants before the reaction will be equal to the total mass of products after the reaction. So, if one of the reactant is present in excess, it would be left unconsumed after the reaction and the mass of the left over reactant will be less than the initial mass of the reactants as the reactants undergo stoichiometric chemical reaction to form the products. But if we consider the mass of reactants and mass of products formed it must be equal as per the Law of conservation of mass which states that mass is neither created nor destroyed it changes.