Chemistry
Stoichiometry
Stoichiometry uses balanced chemical equations to relate amounts of reactants and products. The bridge is always the mole ratio — coefficients in the balanced equation.
How to Approach Stoichiometry
Balance the equation
You can't do stoichiometry on an unbalanced equation. Verify atoms balance on both sides before doing any math.
Convert to moles
Whatever you're given (grams, liters of gas, molecules), convert to moles first using molar mass, molar volume, or Avogadro's number.
Use the mole ratio
Multiply by the ratio of coefficients to get moles of the substance you want. Then convert moles back to your target unit (grams, liters, etc.).
Frequently Asked Questions
What's a limiting reactant?+
The reactant that runs out first — it determines how much product you can make. Find it by computing how much product each reactant could produce on its own; the smaller number wins.
What's percent yield?+
(Actual yield / Theoretical yield) × 100. Real reactions never give 100% yield — losses come from incomplete reaction, side products, or losses during purification.
Do I need to memorize molar masses?+
No — use a periodic table. Sum the atomic masses of each atom in the formula, weighted by subscripts.
Related Topics
More step-by-step guides in Chemistry and adjacent subjects.
Stuck on a Stoichiometry problem?
Snap a photo or type the question. ScanSolve walks you through every step — same as the worked examples above. 5 free solves per day, no card required.