High School Chemistry  ·  Practice by Skill

Stoichiometry Practice Problems

Stoichiometry is how you use a balanced equation to predict how much of a substance a reaction uses up or makes. Here you can practice the three skills it comes down to: mole ratios, limiting reactants, and percent yield. Try the problems below, check your answer, and read the full worked solution.

What you’ll practice

  • Mole-to-mole conversions: use the coefficients in a balanced equation to go from moles of one substance to moles of another.
  • Mass-to-mass problems: chain grams, moles, and a mole ratio together to go from grams of one substance to grams of another.
  • Limiting reactant: work out which reactant runs out first and how much product that allows.
  • Percent yield: compare what you actually collected with what the equation says was possible.

Learn the method first →

A quick example: a mole ratio

How many moles of NH3 form from 1.50 mol of H2?

Read the ratio from the balanced equation: 3 mol H2 makes 2 mol NH3.

Multiply by the ratio so the moles of H2 cancel: 1.50 mol H2 × (2 mol NH3 ÷ 3 mol H2).

N2+3 H2→2 NH3

That gives 1.00 mol NH3.

3 free stoichiometry problems

Give each one a real try before you open the solution. Your answer is checked as soon as you submit it, and the worked solution shows every step so you can see exactly where a setup went wrong.

#1Gram–Gram Stoichiometry
How many grams of CO2 are produced when 20.0 g of CH4 burns completely? CH4 + 2 O2 → CO2 + 2 H2O (MM: CH4 = 16.04 g/mol, CO2 = 44.01 g/mol)
#2Mole Ratio
In the equation CH4 + 2 O2 → CO2 + 2 H2O, how many moles of O2 are needed to react with 3 mol of CH4?
#3Limiting Reactant + Yield
2 H2 + O2 → 2 H2O. You have 3.00 g of H2 and 24.0 g of O2. Which is the limiting reactant, and what is the theoretical yield of H2O? (MM: H2 = 2.016, O2 = 32.00, H2O = 18.02 g/mol)

Questions you might have about stoichiometry

What is stoichiometry?
Stoichiometry is the math of chemical reactions. A balanced equation tells you the ratio of moles of each substance, and stoichiometry uses that ratio to work out how much of one substance you need, or how much you will make, from an amount of another.
How do I find the limiting reactant?
Convert the amount of each reactant to moles, then use the mole ratio to find how much product each one could make. The reactant that makes the least product is the limiting reactant, because it runs out first and stops the reaction.
What is percent yield?
Percent yield compares what you actually collected in the lab (actual yield) with the most the equation says you could make (theoretical yield). Divide actual by theoretical and multiply by 100. It is almost always under 100% because some product gets lost or side reactions happen.
How is stoichiometry different from mole conversions?
A mole conversion changes one substance between grams, moles, and particles using molar mass or Avogadro's number. Stoichiometry adds one more step: a mole ratio from a balanced equation that carries you from one substance to a different one. If you are still shaky on conversions, review the mole first.
High School Chemistry · Stoichiometry Practice Problems