Chemistry: Stoichiometry: Challenge

# Hard Level Guide Stretch thinking with multi-step problems, application questions, and deeper reasoning. # The Mole Concept One mole equals 6.02 × 10²³ particles (Avogadro's number). Molar mass in g/mol converts between grams and moles. For water, 18 g is one mole of H₂O molecules. # Balanced Chemical Equations Coefficients show mole ratios in a reaction. Balance by adjusting coefficients, never subscripts. A balanced equation obeys the law of conservation of mass: atoms are neither created nor destroyed. # Mole-to-Mole Calculations Use coefficients as conversion factors. If 2H₂ + O₂ → 2H₂O, then 2 mol H₂ produces 2 mol H₂O. Set up dimensional analysis: given → moles → moles product → grams if needed. # Limiting Reactant and Percent Yield The limiting reactant runs out first and caps product amount. Excess reactant remains. Percent yield = (actual yield / theoretical yield) × 100%. Real reactions rarely reach 100% due to side reactions and loss.