Zinc and hydrochloric acid react according to the reaction : $$ \mathrm{Zn}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq} .) \longrightarrow \mathrm{ZnCl}_{2}(\mathrm{aq} .)+\mathrm{H}_{2}(\mathrm{~g}) $$ If \(0.30\) mole of \(\mathrm{Zn}\) are added to hydrochloric acid containing \(0.52\) mole HCl, how many moles of \(\mathrm{H}_{2}\) are produced?

Understanding the concept of the limiting reactant is crucial in predicting the amount of products formed in a chemical reaction. It's the substance that is totally consumed when the chemical reaction is complete, determining the maximum amount of product that can be produced. In practical terms, imagine baking cookies: if your recipe calls for one egg per batch and you have five eggs but enough flour for ten batches, you can only make five batches of cookies because eggs are the limiting reactant.
In our zinc and hydrochloric acid reaction, by comparing the moles of each reactant and the stoichiometry, we can identify the limiting reactant. Since hydrochloric acid (HCl) is available in fewer moles than required according to the reaction's stoichiometric ratio, HCl is the limiting reactant. Knowing the limiting reactant is vital for accurate stoichiometry calculations since it allows us to calculate the exact number of moles of products produced in the reaction.

Stoichiometry calculations are mathematical techniques used to determine the amounts of reactants required or products formed in a chemical reaction. These calculations are based on the balanced chemical equation, which provides the mole ratios of reactants and products. In essence, stoichiometry is like a recipe for chemistry. Just as you would use a recipe to find out how much flour and sugar you need for a cake, you use stoichiometry to find out how much of each reactant you need to get your products.
In our exercise, we used the mole ratios from the balanced equation for zinc and hydrochloric acid to calculate the theoretical yield of hydrogen gas (H₂) from Zn and HCl. Such calculations require a clear understanding of the mole concept and the ability to apply the mole ratios to determine the amount of product from a given amount of reactant, which brings us to the mole concept.

The mole concept is one of the central ideas in chemistry and serves as a bridge between the microscopic world of atoms and molecules and the macroscopic world of grams and kilograms that we can measure. One mole is defined as Avogadro's number (\(6.022 \times 10^{23}\)) of particles, whether they are atoms, molecules, ions, or others. It's similar to a dozen eggs being 12 eggs; one mole of any substance is always the same number of particles.
The importance of the mole lies in its ability to relate mass to a count of atoms or molecules. In the context of chemical reactions, being able to convert from moles to grams and vice versa is essential for stoichiometry calculations. Our exercise demonstrated this by converting moles of reactants to moles of products using the balanced equation as the guide.

Chemical reactions involve the transformation of one or more substances into new substances. These changes occur during the breaking and forming of chemical bonds, leading to products that have different properties from the reactants. Every chemical reaction is governed by conservation of mass and follows a balanced equation where the number of atoms of each element in the reactants equals the number of atoms in the products.
In our zinc and hydrochloric acid reaction, the solid zinc reacts with aqueous hydrochloric acid to form aqueous zinc chloride and gaseous hydrogen. This reaction is a type of single displacement reaction, where an element displaces another element in a compound, producing a new compound and an element. Understanding the types of reactions and their mechanisms enables us to predict the products and to carry out appropriate stoichiometry calculations.