What is the mass of the product? a. less than \(10 \mathrm{g}\) b. between 20 and 100 g c. between 100 and \(120 \mathrm{g}\) d. exactly \(120 \mathrm{g}\) e. more than \(120 \mathrm{g}\)

In chemical reactions, the limiting reactant is the substance that is totally consumed first, governing how much of the product can be formed. Imagine you are baking cookies, but run out of sugar after making just a dozen. Sugar is your limiting reactant because it limits the number of cookies you can bake. Similarly, in a chemical reaction, identifying the limiting reactant is critical, as it dictates the maximum quantity of products that can be made.
When multiple reactants are mixed, there often isn't a perfect amount of each. One will be in shorter supply relative to the amounts dictated by the balanced chemical equation. To find out which reactant will limit the reaction, a comparison is made between the reactants' molar amounts and the ratios in which they react. The one present in the least amount, according to these ratios, is the limiting reactant. Once it's used up, the reaction stops, regardless of how much of the other reactants remain, akin to our sugar and cookies analogy.

A balanced chemical equation is similar to a recipe for a reaction. Just as a recipe tells you how much of each ingredient to use, a balanced chemical equation shows the exact ratio of reactants needed to form products. Each molecule's representation comes with coefficients indicating the number of molecules involved. Balancing is crucial because it ensures that the law of conservation of mass is obeyed; the number of atoms for each element is the same on both sides of the equation.
Balancing equations enables us to perform stoichiometric calculations effectively. We can predict the amount of product formed from given quantities of reactants because the coefficients directly translate to molar ratios. These ratios can then be used as conversion factors in calculations. For example, if your equation suggests that one molecule of hydrogen reacts with one molecule of oxygen to produce two molecules of water (2H2 + O2 -> 2H2O), the balanced equation indicates it takes two molecules of hydrogen (2H2) to react completely with one molecule of oxygen (O2). Thus, hydrogen and oxygen are in a 2:1 ratio.

The molar mass is akin to the weight of one mole of a substance, measured in grams per mole (g/mol). A mole is a specific number of particles (6.022 x 10^23, known as Avogadro's number), making molar mass a bridge between the microscopic world of atoms and molecules and the macroscopic world we live in. Knowing the molar mass of a substance allows us to convert between the mass of a substance and the number of moles.
Molar mass is determined by adding up the atomic masses of all the atoms in a molecule. For example, water (H2O) has a molar mass of approximately 18 g/mol (16 for oxygen and 1 each for the two hydrogens). When doing stoichiometric calculations, molar mass serves as a conversion factor enabling the determination of how many grams are needed for a reaction or produced by it. It's a fundamental component in calculating the quantities involved in chemical reactions.

Stoichiometric calculations are the bread and butter of chemical stoichiometry. They are how we apply the balanced chemical equation to find out how much reactants will be consumed or how much product will be formed in a reaction. These calculations rely heavily on the concept of the mole and use molar mass as a conversion factor.
For instance, they allow us to determine the limiting reactant by comparing the mole ratio of the reactants used to the mole ratios in the balanced chemical equation. With this approach, students can apply known quantities, such as the mass of reactants, to find unknown quantities, like the mass of the product. The process generally involves converting mass to moles, using the molar ratios from the balanced equation to find the stoichiometry of the reaction, and then, if necessary, converting back to grams to find the mass of the products. It's like figuring out how many batches of cookies you can bake based on the amount of sugar and flour you have—knowing that you'll always need them in a specific ratio for your recipe to work out.