reactions-stoichiometrylisted

# Reactions and Stoichiometry Chemical reactions transform substances by breaking and forming bonds. Stoichiometry is the quantitative bookkeeping — tracking atoms, moles, and energy through these transformations. This skill covers equation balancing, reaction classification, mole-based calculations, acid-base chemistry, redox reactions, and thermochemistry. **Agent affinity:** lavoisier (chair, reactions and conservation of mass, primary) **Concept IDs:** chem-balancing-equations, chem-reaction-types, chem-acids-bases, chem-oxidation-reduction, chem-thermochemistry ## Conservation of Mass and Balancing Equations **Lavoisier's Law.** In a chemical reaction, matter is neither created nor destroyed. Every atom present in the reactants must appear in the products. **Balancing procedure:** 1. Write the unbalanced equation with correct formulas. 2. Balance one element at a time, starting with the most complex molecule. 3. Balance hydrogen and oxygen last (they appear in many compounds). 4. Use the smallest whole-number coefficients. 5. Verify: count every element on both sides. ### Worked Example: Combustion of Propane **Unbalanced:** C3H8 + O2 -> CO2 + H2O **Step 1.** Balance C: 3 carbons on left, so 3 CO2 on right. C3H8 + O2 -> 3 CO2 + H2O **Step 2.** Balance H: 8 hydrogens on left, so 4 H2O on right. C3H8 + O2 -> 3 CO2 + 4 H2O **Step 3.** Balance O: Right side has 3(2) + 4(1) = 10 oxygens. Left needs 10/2 = 5 O2. C3H8 + 5 O2 -> 3 CO2 + 4 H2O **Verify:** C: 3 = 3. H