Ammonia is a principal nitrogen fertilizer. It is prepared by the reaction between hydrogen and nitrogen.$$3 \mathrm{H}_{2}(g)+\mathrm{N}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$$In a particular reaction, 6.0 moles of \(\mathrm{NH}_{3}\) were produced. How many moles of \(\mathrm{H}_{2}\) and how many moles of \(\mathrm{N}_{2}\) were reacted to produce this amount of \(\mathrm{NH}_{3} ?\)

Chemical reaction balancing is an essential skill one needs to master when studying chemistry. It ensures that the law of conservation of mass is obeyed in a chemical equation. In simple terms, what goes into a reaction must equal what comes out, and this includes every atom involved in the process. For example, in the ammonia synthesis reaction provided,
\(3H_2(g) + N_2(g) \longrightarrow 2NH_3(g)\),
we can see that there are 6 hydrogen atoms on the left side (3 moles of \(H_2\), with each \(H_2\) having 2 hydrogen atoms) and 6 hydrogen atoms on the right side (2 moles of \(NH_3\), with each \(NH_3\) having 3 hydrogen atoms). The nitrogen atoms also balance with 2 on both sides.

Counting Atoms for Balancing

When balancing a chemical equation, it is important to count the number of atoms for each element on both sides of the equation and adjust the coefficients to balance them. Coefficients are the numbers placed before the chemical formulas and represent the moles of that substance. Adjusting the coefficients changes the number of atoms or molecules in the chemical equation so that the reactants and products have the same number of each type of atom. This balanced equation becomes the blueprint for any further calculations related to the reaction.

The mole concept is a way of expressing the amount of a substance. It is part of the international system of units and is defined as the amount of substance that contains as many entities (atoms, ions, molecules, etc.) as there are atoms in exactly 12 grams of carbon-12. This amounts to Avogadro's number (approximately \(6.022 \times 10^{23}\) entities). Understanding the mole concept allows chemists to count particles by weighing them.
In the ammonia production exercise, we are told that 6.0 moles of ammonia are produced. Using six moles isn't about the weight of the ammonia but about the number of molecules. One mole of any substance always contains the same number of entities – Avogadro's number. This concept helps in establishing a link between the microscopic particles and the macroscopic amounts we can measure, allowing us to quantify the amount of reactants used and products formed in a chemical reaction.

Stoichiometric calculations involve using the relationships in a balanced chemical equation to determine the quantities of reactants and products. By applying the mole concept to the coefficients in the balanced equation, we can calculate how much of each reactant is needed to produce a desired amount of product.

Stoichiometric Ratios

In the given ammonia synthesis example, the stoichiometric ratio between hydrogen and ammonia is 3:2, and between nitrogen and ammonia is 1:2. These ratios tell us how many moles of each reactant are needed per mole of product formed. Therefore, if we produce 6 moles of ammonia, we can quickly determine the moles of hydrogen and nitrogen used in the reaction by using these fixed ratios. The concept is vital in chemical manufacturing and laboratory work because it allows for the precise calculation of reactant amounts, minimizing waste and optimizing reaction conditions. By mastering stoichiometry, one can confidently scale-up reactions from the lab bench to industrial production levels.