Stoichiometry is the quantitative side of chemistry — writing formulae, balancing equations, and calculating masses, moles, and concentrations in chemical reactions.
Chemical formulae show the ratio of atoms in a compound. Empirical formula: simplest whole number ratio. Molecular formula: actual number of atoms. Balancing equations: same number of each type of atom on both sides. State symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution. Ionic equations show only the ions that change.
Mole: 6.02 × 10²³ particles (Avogadro\'s number). Molar mass M (g/mol) = relative formula mass. n = m/M (moles = mass/molar mass). Molar gas volume: 24 dm³ at room temperature and pressure. n = V/24. Use balanced equations to convert between moles of different substances. Percentage composition = (mass of element / molar mass of compound) × 100%.
Concentration c = n/V (mol/dm³) or c = m/V (g/dm³). Dilution: c₁V₁ = c₂V₂. Titration calculations: use balanced equation to find unknown concentration. Percentage yield = (actual yield / theoretical yield) × 100%. Yield < 100% due to: incomplete reaction, side reactions, losses during transfer/purification.
The empirical formula is the simplest whole-number ratio of atoms in a compound (e.g., CH₂O). The molecular formula shows the actual number of each atom (e.g., C₆H₁₂O₆ = glucose). To find the molecular formula from the empirical: divide the relative molecular mass by the empirical formula mass to get a multiplier, then multiply subscripts. Some compounds have the same empirical and molecular formula (e.g., H₂O).
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