Unit 4 covers chemical reactions — classifying them, writing net ionic equations, and performing stoichiometric calculations including limiting reagent and percent yield problems.
Synthesis (A + B → AB), decomposition (AB → A + B), single replacement (A + BC → AC + B), double replacement (AB + CD → AD + CB). Precipitation: insoluble product forms. Acid-base: H⁺ + OH⁻ → H₂O. Redox: electron transfer (oxidation = loss, reduction = gain). Net ionic equations: remove spectator ions, show only species that change.
Mole ratio from balanced equation. Convert: mass → moles → mole ratio → moles → mass. Molar mass from periodic table. Limiting reagent: reactant that runs out first — determines product amount. Excess reagent: leftover after reaction. Percent yield = (actual/theoretical) × 100%. Solution stoichiometry: moles = molarity × volume (in L). Dilution: M₁V₁ = M₂V₂.
Method: (1) Convert each reactant to moles (mass/molar mass or M×V for solutions). (2) Use the balanced equation to find the mole ratio required. (3) Determine which reactant provides fewer moles of product — that is the limiting reagent. Alternative: divide each reactant\'s moles by its coefficient; the smallest value identifies the limiting reagent. All calculations (product mass, percent yield) are based on the limiting reagent. The other reactant is in excess — calculate how much is left over by finding how much reacted.
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