What volume of 2.0 M hydrochloric acid solution will be consumed when it reacts with 5 grams of magnesium to form magnesium chloride and hydrogen gas? 2HCl + Mg -> MgCl2 + H2​

Explanation:

Remember, matter can neither be created nor destroyed, so every atom of reactant the leftt side of the equation must be accounted for in the products on the right side of the equation. With  magnesium and hydrochloric acid we have:  Mg  +  2HCl   →  MgCl2  +  H2(g).  Magnesium is divalent, and so requires two chloride ions to form magnesium chloride.  Hydrogen gas is a diatomic molecule, so the reaction requires the product to be H2.  Going across the equation from left to right we have 1 atom of magnesium (accounted for on the right side of the equation), and on the left, 2 moles of hydrochloric acid; the two hydrogens represented on the left of the equation are accounted for on the right of the equation.  Likewise, the two chloride anions on the left of the equation are accounted for in the formation of MgCl2 on the right. When all the atoms are accounted for on both sides of the equation, we say the equation is "balanced".