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Chemical formulas are crucial in chemistry as they provide a shorthand way of representing the composition of molecules and compounds. These formulas indicate the type and number of atoms in a molecule. For example, in the original exercise, the chemical formula of tetrahydrocannabinol (THC) is \(\text{C}_{21}\text{H}_{30}\text{O}_{2}\). This illustrates that each molecule of THC consists of 21 carbon atoms, 30 hydrogen atoms, and 2 oxygen atoms.
The subscripts in a chemical formula convey the moles of each element in one mole of the compound. By understanding chemical formulas, scientists can easily determine the proportions of different elements in a substance and calculate properties like molar mass. Recognizing these formulas is essential for performing further calculations based on the mole concept or other chemical principles.

The mole concept is a fundamental principle in chemistry that allows chemists to count particles, such as atoms and molecules, using a measurable quantity. One mole of any substance contains the same number of particles, which facilitates calculations between the mass and number of atoms in a sample.
The mole concept ties the macroscopic world of grams and liters to the microscopic world of atoms and molecules. By using the formula \(\text{moles} = \frac{\text{mass}}{\text{molar mass}}\), we can determine the number of moles of a substance when given the mass and the molar mass. In the exercise, converting 25 碌g of THC into moles helps us transition from a tiny mass into an understandable quantity on the mole scale. This allows us to further compute how many molecules we are considering.

Avogadro's number is a key constant in chemistry, defined as \(6.022 \times 10^{23}\) particles per mole. It provides the link between the macroscopic scale (that we can measure) and the atomic scale (which we cannot directly observe).
For instance, once we know the number of moles of THC, Avogadro's number allows us to calculate the exact number of molecules in that amount. By multiplying the moles obtained from the mass by Avogadro's number \((\text{moles} \times 6.022 \times 10^{23})\), students can transition from grams to individual molecules. This tool is invaluable for understanding reactions as it bridges the gap between the scale of laboratory measurements and molecular interactions.