Stoichiometry

Moles and Formulas

The mole ($6.022 \times 10^{23}$ particles) links mass to particle count through molar mass: $n = \frac{m}{M}$ Percent composition and combustion data yield the empirical formula; the molecular formula is a whole-number multiple of it, found by comparing empirical mass to molar mass.

Limiting Reagent and Yield

Convert every reactant to moles, divide by its coefficient, and the smallest ratio identifies the limiting reagent, which fixes theoretical yield. Percent yield is actual over theoretical times 100. Recognize reaction types: combination, decomposition, single/double displacement, and combustion.

Solutions and Gases

Molarity ($\text{mol/L}$) drives solution stoichiometry, and dilutions conserve moles of solute: $M_1V_1 = M_2V_2$ Gas problems use the ideal gas law $PV = nRT$ with STP molar volume $22.4\ \text{L}$, Dalton's law for partial pressures ($P_i = X_iP_{total}$), and Faraday's law to convert charge passed ($q = It$) into moles of electrons and deposited metal. Real gases deviate at high pressure and low temperature.

Key Takeaways

• Mole ratios from the balanced equation are the bridge in every calculation.
• The limiting reagent, not the total reactants, sets the theoretical yield.
• Dilution and titration problems conserve moles: $M_1V_1 = M_2V_2$.
• One mole of ideal gas occupies 22.4 L at STP; deviations grow when molecules attract or crowd.