Chemical Composition, Molar Mass, and Stoichiometry

Chemical Composition

• A mole is a counting unit for atoms
• $1 \text{ mol} = 6.022 \times 10^{23} \text{ things}$ where "things" can be molecules, atoms, ions, electrons
• The mass of 1 mol of "things" in grams equals the average mass of one "thing" in atomic mass units (amu)

Molar Mass

• Molar mass is the mass in grams of one mole of a substance
• Molar mass is numerically equal to the atomic mass in amu
• 1 mol of carbon-12 has a mass of 12 grams

Percent Composition

• Percent composition is the mass percent of each element in a compound
• $\text{Mass } % = \frac{\text{mass of element in 1 mol of compound}}{\text{mass of 1 mol of compound}} \times 100$

Stoichiometry

• Stoichiometry uses balanced chemical equations to determine the relative masses of reactants and products

Mole Ratios

• Mole ratios convert moles of one substance to moles of another
• Mole ratios are derived from the coefficients of a balanced chemical equation
• In the equation $aA + bB \rightarrow cC + dD$, mole ratios include: $\frac{a \text{ mol } A}{b \text{ mol } B}$, $\frac{a \text{ mol } A}{c \text{ mol } C}$, $\frac{a \text{ mol } A}{d \text{ mol } D}$

Limiting Reactant

• The limiting reactant is fully consumed in a chemical reaction
• The limiting reactant dictates the amount of product formed

Theoretical Yield

• Theoretical yield is the product amount formed when the limiting reactant is fully consumed

Percent Yield

• The actual yield is the amount of product obtained from a reaction
• $\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$ gives the percent yield, measuring reaction efficiency