Question

q.3 why is the number of moles of hcl divided by 2 when it is compared to the number of moles of magnesium for determining the limiting reactant?

Explanation:

The reaction between magnesium (\(Mg\)) and hydrochloric acid (\(HCl\)) is \(Mg + 2HCl=MgCl_{2}+H_{2}\uparrow\). According to the stoichiometric ratio in the chemical equation, the mole ratio of \(Mg\) to \(HCl\) is \(1:2\). When determining the limiting reactant, we need to compare the available moles of reactants based on their stoichiometric relationship. So, the moles of \(HCl\) are divided by \(2\) (its stoichiometric coefficient) to make it comparable to the moles of \(Mg\) (with a stoichiometric coefficient of \(1\)).

Answer:

Because in the chemical reaction \(Mg + 2HCl = MgCl_{2}+H_{2}\uparrow\), the stoichiometric ratio of \(Mg\) to \(HCl\) is \(1:2\). Dividing the moles of \(HCl\) by \(2\) allows for a direct comparison with the moles of \(Mg\) (on a per - “reaction unit” basis) to determine which reactant will be consumed first (the limiting reactant).