Stoichiometry is the study of quantitative relationships in chemical reactions. The coefficients in a balanced equation give the mole ratios of reactants and products.
Core Equations
\( n = \frac{m}{M} \) (mass → moles)
\( n = cV \) (solution: concentration × volume in dm³)
\( n = \frac{V}{V_m} \) (gas at STP: Vm = 22.7 dm³ mol⁻¹)
The Stoichiometry Bridge
Convert → Moles of known → Mole ratio → Moles of unknown → Convert
Worked Example
What mass of CO₂ forms when 10.0 g of CaCO₃ decomposes?
CaCO₃(s) → CaO(s) + CO₂(g)
1. Moles CaCO₃ = 10.0 / 100.09 = 0.0999 mol
2. Mole ratio CaCO₃ : CO₂ = 1 : 1
3. Moles CO₂ = 0.0999 mol
4. Mass CO₂ = 0.0999 × 44.01
= 4.40 g
Think About It
In the above example, what volume would the CO₂ occupy at STP?
V = n × Vm = 0.0999 × 22.7 = 2.27 dm³