Determine the number of moles of the compound and determine the number of moles of each type of atom in each of the following: (a) 2.345 mol LiCl (b) 0.0872 mol acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) \(3.3 \times 10^{-2} \mathrm{mol} \mathrm{Na}_{2} \mathrm{CO}_{3}\) (d) \(1.23 \times 10^{3}\) mol fructose, \(C_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (e) 0.5758 mol \(\operatorname{FeSO}_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{7}\)

Stoichiometry is a branch of chemistry that deals with the quantitative relationship between reactants and products in a chemical reaction. It allows us to calculate the amounts of substances involved in reactions based on balanced chemical equations. Think of it as a form of 'chemical accounting', where the mole concept plays a crucial role.

In essence, stoichiometry connects the macroscopic world we can measure (like mass in grams) to the microscopic world of atoms and molecules, using the mole as a bridging unit. A mole is like a chemist's dozen, a standard quantity (Avogadro's number, which is approximately \(6.022 \times 10^{23}\)) of particles. Knowing that each molecule of a substance contains a definite number of atoms, stoichiometry uses this information to work out the detailed atomic accounting within chemical reactions.

For example, if a reaction requires one mole of hydrogen gas (\(H_2\)) and yields two moles of water (\(H_2O\)), stoichiometry helps determine the amount of each reactant required to produce a desired amount of product.

Atomic composition refers to the type and number of atoms that constitute a particular chemical species (like an element or compound). In a molecular formula, the subscript after each element symbol indicates the number of atoms of that element in one molecule of the compound. Understanding the atomic composition is vital for executing chemical calculations and stoichiometry.

When solving chemical problems, we often use molecular formulas to infer the atomic composition. This information helps us calculate the number of moles of each element in a given mass or number of moles of a compound. The exercise given, demonstrates how to derive the number of moles of individual atoms from the number of moles of the compound, highlighting the direct relationship between the molecular formula and the mole ratio of its constituent elements.

Molecular composition describes the type and quantity of atoms making up a molecule. Unlike atomic composition, which only details the types of atoms, molecular composition explains how these atoms are bonded together. For example, \(C_6H_{12}O_6\) indicates not just the presence of carbon, hydrogen, and oxygen, but also that these elements are connected in a specific arrangement to form a fructose molecule.

In the context of the given exercise, understanding the molecular composition allows us to determine the number of moles of individual elements present in a mole of the compound. It involves multiplying the number of moles of the compound by the number of atoms of each element represented in the compound's molecular formula.

Chemical calculations are the backbone of understanding and predicting the outcomes of chemical reactions. These calculations typically rely on the mole concept and balanced chemical equations to ensure that the law of conservation of mass is observed. One of the main calculation types is determining the number of moles of reactants and products.

As illustrated in the solution steps for various compounds, such calculations may involve converting mass to moles or moles to particles and vice versa. By following a methodical approach to solving these problems, such as identifying the correct molecular or empirical formulas and using stoichiometric coefficients from balanced equations, we can accurately quantify substance amounts throughout chemical processes. These skills are fundamental for both practical laboratory work and theoretical studies in chemistry.