Chemical Calculations: Formula Masses, Moles, and Chemical Equations

Vocabulary terms covering formula masses, mole concepts, Avogadro's number, stoichiometry, and balancing chemical equations based on the lecture notes.

Formula mass

The sum of the atomic masses of all the atoms represented in the chemical formula of a substance, expressed in atomic mass units ($amu$).

Formula Weight (FW)

The sum of the atomic weights for the atoms in a chemical formula; for an element it is the atomic weight, and for an ionic compound, the empirical formula is used.

Molecular Weight (MW)

The sum of the atomic weights of the atoms in a molecule; it is the term used for formula weight when the substance is a molecule.

Mole (mol)

The amount of particles found in exactly $12\,g$ of $C-12$, representing a counting unit equal to Avogadro's number.

Avogadro’s number ($N_A$)

A value representing the number of atoms or molecules in one mole, used as a conversion factor; this text uses the value $6.02 \times 10^{23}$.

Molar mass

The mass, in grams, of 1 mole of a substance that is numerically equal to the substance’s formula mass.

Formula ratio

The ratio of the number of atoms of an element in a compound per one unit of the compound, derived from the subscripts of the chemical formula.

Chemical equation

A written statement that uses chemical symbols and chemical formulas instead of words to describe the changes that occur in a chemical reaction.

Reactants

The starting materials in a chemical reaction that undergo change, written on the left side of the chemical equation.

Products

The substances produced as a result of a chemical reaction, written on the right side of the chemical equation.

Equation coefficient

A whole number placed to the left of a chemical formula in an equation that changes the amount, but not the identity, of the substance.

Balanced chemical equation

A chemical equation that has the same number of atoms of each element involved in the reaction on both the reactant and product sides.

Law of Conservation of Mass

A law stating that mass is neither created nor destroyed during a chemical reaction, and that the sum of the masses of the reactants equals the sum of the masses of the products.

Molar ratio

A ratio of the coefficients expressed in moles for two different substances in the same balanced chemical reaction.

Theoretical yield

The maximum amount of a product that can be obtained from given amounts of reactants in a chemical reaction if no losses occur.

Actual yield

The amount of product actually obtained from a chemical reaction, which is typically less than the theoretical yield due to inefficiencies.

Percent yield

The ratio of the actual yield of a product to the theoretical yield multiplied by $100\%$. ($\text{Percent yield} = \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100\%$)