The universal stoichiometry path
Every problem follows this route
grams A → moles A → (coefficient ratio) → moles B → grams B
Coefficients in a balanced equation are mole ratios — they say nothing about grams directly. That's why every mass must be converted to moles before the ratio applies, and back afterwards. Molar masses (from the molar mass calculator) are the exchange rate for both conversions.
Worked example
How many grams of NH₃ form from 28.0 g of N₂? (N₂ + 3H₂ → 2NH₃)
- Moles N₂ = 28.0 ÷ 28.01 = 1.00 mol
- Ratio NH₃:N₂ = 2:1 → 2.00 mol NH₃
- Mass = 2.00 × 17.03 g/mol
Answer: ≈ 34.1 g of ammonia.
Common mistakes
⚠ Common mistake: Applying the coefficient ratio to grams directly. 2 g of H₂ does not give 2 g of H₂O — ratios work on moles only.
⚠ Common mistake: Using an unbalanced equation. This tool balances for you, but on paper always balance first — wrong coefficients mean wrong ratios.
⚠ Common mistake: Grabbing the wrong molar mass in the final step — use the target substance's molar mass, not the known one's.