Gas Stoichiometry
Gas volumes relate to moles at the same conditions.
About this topic
Gas stoichiometry applies mole ratios to reactions involving gases. At STP (0 °C, 1 atm), one mole of any ideal gas occupies 22.4 L. For other conditions, use PV = nRT with R = 0.0821 L·atm/(mol·K) to convert between moles and volume. Gay-Lussac's law says that gas volumes in a reaction at constant conditions are in the same ratio as the coefficients.
The method is: convert what you are given to moles, use the mole ratio, then convert to the quantity you want, such as volume of gas. Temperature must be in kelvin. Avogadro's law explains why gas volumes in simple ratios match mole ratios: equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
Worked example: how much hydrogen forms when 6.54 g of zinc reacts with acid? Zn + 2HCl gives ZnCl2 + H2, and 6.54 g of zinc is 0.100 mol, so 0.100 mol of H2 forms, which is 2.24 L at STP. Car airbags rely on sodium azide decomposing to give nitrogen gas rapidly: engineers calculate exactly how much solid is needed to fill a bag with about 60 litres.
Students often use 22.4 L/mol at room temperature (it is about 24.5 L there) or forget to convert degrees Celsius to kelvin.
Key ideas
- 22.4 L/mol at STP
- Use PV = nRT otherwise
- Avogadro's law
Quick check
Use cases: where Gas Stoichiometry helps
- Homework: review the key idea behind Gas Stoichiometry before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Gas Stoichiometry without notes.
- Visual learning: play with the interactive lab to see how Gas Stoichiometry changes when you adjust its inputs.
- Teaching a friend: explain Gas Stoichiometry 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 Gas Stoichiometry?
Gas volumes relate to moles at the same conditions.
What will I learn in Gas Stoichiometry?
22.4 L/mol at STP. Use PV = nRT otherwise. Avogadro's law.
Is Gas Stoichiometry 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 Gas Stoichiometry 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 Gas Stoichiometry?
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.