Stoichiometry

Converting between mass, moles, and particles using balanced equations

Golden Rule: Everything goes through moles. Mass → moles (÷ molar mass) → moles of target (× mole ratio) → desired unit.

• Step 1: Write and balance the chemical equation — Balance by adjusting stoichiometric coefficients — never change subscripts. The coefficients give the mole ratios between all species.
• Step 2: Convert given quantity to moles — From mass: n = mass / M. From volume of solution: n = C × V (use consistent units, liters for C in mol/L). From gas at STP: n = V / 22.4 L.
• Step 3: Apply the mole ratio — From the balanced equation, write: n(target) = n(given) × [coefficient of target / coefficient of given].
• Step 4: Convert moles to requested unit — To mass: m = n × M. To particles: N = n × 6.022 × 10²³. To volume (gas at STP): V = n × 22.4 L. To solution volume: V = n / C.