Mole Ratios
Coefficients give mole ratios between substances.
About this topic
Mole ratios come from the coefficients in a balanced equation and tell how many moles of one substance react with or form from another. In 2H2 + O2 → 2H2O, the ratios are 2 mol H2 : 1 mol O2 : 2 mol H2O. They are the bridge in every stoichiometry calculation.
A mole ratio is written as a fraction, with the substance you want on top and the substance you have on the bottom, so units cancel. For example, to find the moles of water from 3.0 mol of hydrogen, multiply by 2 mol H2O over 2 mol H2, giving 3.0 mol H2O. The ratio only works if the equation is balanced, which is why balancing comes first. Ratios are about moles, not grams or litres of liquids and solids; for gases at the same conditions, volume ratios match mole ratios.
Think of a recipe: two slices of bread and one slice of cheese make one sandwich, so with 10 slices of bread you can use 5 slices of cheese. Chemists use this to decide how much reactant to buy and how much product to expect. In the Haber process, N2 + 3H2 gives 2NH3, so three times as much hydrogen as nitrogen is needed.
A common error is using the subscripts instead of coefficients, or using a ratio from an unbalanced equation. Also, do not compare masses directly; always convert to moles first.
Key ideas
- 2H₂ + O₂ → 2H₂O
- Use ratios to convert
- Core of stoichiometry
Quick check
Use cases: where Mole Ratios helps
- Homework: review the key idea behind Mole Ratios before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Mole Ratios without notes.
- Visual learning: play with the interactive lab to see how Mole Ratios changes when you adjust its inputs.
- Teaching a friend: explain Mole Ratios in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Mole Ratios?
Coefficients give mole ratios between substances.
What will I learn in Mole Ratios?
2H₂ + O₂ → 2H₂O. Use ratios to convert. Core of stoichiometry.
Is Mole Ratios part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Mole Ratios lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Mole Ratios?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.