Stoichiometry — Molar Ratios & Conversions
Calculate molar ratios, convert between moles, grams, and molecules. Solve stoichiometric problems using balanced chemical equations.
Why This Scientific Calculation Matters
Why: Stoichiometry predicts quantities in chemical reactions. Molar ratios from balanced equations connect reactants and products.
How: Enter a balanced equation, given substance, target substance, amount, and units. Convert through moles using molar ratios.
- ●Always convert to moles first
- ●Molar ratio = coeff_target / coeff_given
- ●N_A = 6.022×10²³
⚗️ Quick Examples — Click to Load
Input Values
🧪 Scientific Discoveries
One mole of water = 6.022×10²³ molecules
— IUPAC
Mole concept by Ostwald, 1893
— History
Haber-Bosch: 150M tons NH₃/yr
— Industrial
📋 Key Takeaways
- • Stoichiometry is the quantitative relationship between reactants and products in chemical reactions
- • Molar ratios come directly from coefficients in balanced equations — 2H₂ + O₂ → 2H₂O means 2:1:2 ratio
- • Always convert to moles first, then use molar ratios, then convert to desired units
- • Avogadro's number (6.022 × 10²³) connects moles to actual particle counts
- • Molar mass (g/mol) converts between grams and moles — essential for all stoichiometry
💡 Did You Know?
📖 How Stoichiometry Works
Stoichiometry allows you to predict quantities in chemical reactions using balanced equations and molar relationships.
Step 1: Balance the Equation
Ensure atoms are conserved: 2H₂ + O₂ → 2H₂O (not H₂ + O₂ → H₂O). Coefficients tell you the molar ratios.
Step 2: Convert to Moles
Convert your given quantity to moles: grams → moles (divide by molar mass), molecules → moles (divide by Avogadro's number).
Step 3: Apply Molar Ratio
Use coefficients to find moles of target: n_target = n_given × (coefficient_target / coefficient_given).
Step 4: Convert to Desired Units
Convert moles to grams (multiply by molar mass) or molecules (multiply by Avogadro's number).
📐 Key Formulas
🎯 Expert Tips
💡 Always Check Units
Molar mass has units g/mol. When converting grams to moles, grams cancel out: g ÷ (g/mol) = mol. Always track units to catch errors!
💡 Limiting Reagent
The limiting reagent determines maximum product. Calculate moles of product from each reactant — the smallest result is your answer.
💡 Significant Figures
Your answer should match the precision of your input. If given 2.0 moles, report to 2 significant figures. Molar masses are typically known to 3-4 sig figs.
💡 Percent Yield
Actual yield is often less than theoretical (from stoichiometry) due to side reactions, incomplete reactions, or losses. Percent yield = (actual/theoretical) × 100%.
⚖️ Common Molar Masses Reference
| Substance | Formula | Molar Mass (g/mol) | Common Use |
|---|---|---|---|
| Water | H₂O | 18.015 | Solvent, life |
| Carbon Dioxide | CO₂ | 44.009 | Respiration, photosynthesis |
| Ammonia | NH₃ | 17.031 | Fertilizer production |
| Methane | CH₄ | 16.043 | Natural gas, fuel |
| Sodium Chloride | NaCl | 58.443 | Table salt |
| Calcium Carbonate | CaCO₃ | 100.087 | Limestone, antacids |
| Glucose | C₆H₁₂O₆ | 180.156 | Energy in cells |
| Ethanol | C₂H₅OH | 46.069 | Alcohol, fuel |
❓ Frequently Asked Questions
What is stoichiometry?
Stoichiometry is the calculation of quantities in chemical reactions using balanced equations. It allows you to predict how much product forms from given reactants, or how much reactant is needed for desired products.
How do I find molar mass?
Molar mass is the sum of atomic masses in a compound. For H₂O: 2×H (1.008) + O (15.999) = 18.015 g/mol. Look up atomic masses from the periodic table and multiply by subscripts.
What is Avogadro's number?
Avogadro's number (6.022 × 10²³) is the number of particles (atoms, molecules, ions) in one mole. It connects the macroscopic world (grams) to the microscopic world (molecules).
How do I balance chemical equations?
Balance by adjusting coefficients so atoms are conserved. Start with elements that appear in only one compound on each side. Use trial and error or algebraic methods. This calculator requires already-balanced equations.
What is a limiting reagent?
The limiting reagent is the reactant that runs out first, limiting product formation. Calculate moles of product from each reactant using stoichiometry — the smallest result identifies the limiting reagent.
Can I convert directly between grams and molecules?
No, you must go through moles: grams → moles (÷ molar mass) → molecules (× Avogadro's number). Moles are the "bridge" between mass and particle count.
📊 Stoichiometry by the Numbers
📚 Official Data Sources
⚠️ Disclaimer: This calculator requires balanced chemical equations. Complex formulas with polyatomic ions, hydrates, or organic compounds may require manual verification. Molar masses are approximate — use exact values from NIST for precise work. Always verify equation balancing before calculations.
⚠️For educational and informational purposes only. Verify with a qualified professional.