Combined and Ideal Gas Laws
PV = nRT combines every gas law.
About this topic
The combined gas law merges Boyle's, Charles's and Gay-Lussac's laws: P1V1/T1 = P2V2/T2 for a fixed amount of gas. The ideal gas law, PV = nRT, includes the amount of gas, with R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K). It lets you find any one of pressure, volume, moles or temperature from the other three.
The combined law is handy when two or three variables change together. The ideal gas law works from a single set of conditions and can be used to find the molar mass of a gas (M = mRT / PV) or its density (d = PM / RT). Temperature must always be in kelvin, and the units of R must fit your pressure and volume. The ideal gas is a model: it works best at high temperature and low pressure, when particles are far apart.
Worked example: how many moles are in 5.00 L of gas at 2.00 atm and 300 K? n = PV / RT = (2.00 x 5.00) / (0.0821 x 300) = 0.406 mol. Standard molar volume of 22.4 L at STP follows from the same equation. Applications include inflating airbags, scuba tanks, weather balloons and industrial gas storage.
Typical mistakes are using Celsius, using the wrong value of R for the units, and applying the laws to liquids or solids. Remember that real gases deviate near condensation.
Key ideas
- R = 8.314 J/mol·K
- Use kelvin and consistent units
- Real gases deviate at high P, low T
Quick check
Use cases: where Combined and Ideal Gas Laws helps
- Homework: review the key idea behind Combined and Ideal Gas Laws before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Combined and Ideal Gas Laws without notes.
- Visual learning: play with the interactive lab to see how Combined and Ideal Gas Laws changes when you adjust its inputs.
- Teaching a friend: explain Combined and Ideal Gas Laws 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 Combined and Ideal Gas Laws?
PV = nRT combines every gas law.
What will I learn in Combined and Ideal Gas Laws?
R = 8.314 J/mol·K. Use kelvin and consistent units. Real gases deviate at high P, low T.
Is Combined and Ideal Gas Laws 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 Combined and Ideal Gas Laws 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 Combined and Ideal Gas Laws?
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.