Stoichiometry
Definition
The calculation of reactants and products in chemical reactions using balanced equations and molar ratios.
Why is Stoichiometry Important?
Stoichiometry is an essential chemistry concept used in laboratories, pharmaceutical development, environmental science, and industrial processes. Understanding this concept is critical for accurate chemical calculations, safe laboratory practices, and optimizing reactions.
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What is Stoichiometry?
Stoichiometry is the calculation of quantities of reactants and products in chemical reactions based on balanced chemical equations. It uses molar ratios from balanced equations to predict how much of each substance is needed or produced.
Stoichiometry Steps
| Step | Action | Example: 2H₂ + O₂ → 2H₂O |
|---|---|---|
| 1 | Balance the equation | Already balanced: 2:1:2 |
| 2 | Convert given to moles | 10 g H₂ ÷ 2.016 g/mol = 4.96 mol H₂ |
| 3 | Use molar ratio | 4.96 mol H₂ × (1 mol O₂ / 2 mol H₂) = 2.48 mol O₂ |
| 4 | Convert to desired units | 2.48 mol O₂ × 32.00 g/mol = 79.4 g O₂ |
Key Stoichiometry Concepts
- Molar ratio: Coefficients in balanced equation give the mole ratio (2H₂:1O₂:2H₂O)
- Limiting reagent: The reactant that runs out first, limiting the product formed
- Excess reagent: The reactant left over after the reaction completes
- Theoretical yield: Maximum product possible from stoichiometry
- Actual yield: What you actually collect (always less due to losses)
- Percent yield: (Actual / Theoretical) × 100%