The PhET Gas Properties lab is one of the best ways to make the gas laws visible. Instead of memorizing PV = nRT, students pump particles into a box, heat it, shrink it and watch the pressure gauge respond in real time. The free simulation from the University of Colorado Boulder runs in any browser, so it works on Chromebooks, laptops and tablets with no installation.
This guide gives you a complete, classroom-ready structure: a pre-lab question, four investigations that match the simulation’s screens, a data table, analysis questions and quick answers to common teacher questions. It fits chemistry and physical science classes and takes one or two 50-minute periods.
In this guide11 sections
- What students learn
- Getting started
- Investigation 1: What causes pressure? (Explore screen)
- Investigation 2: Boyle’s law (Ideal screen)
- Investigation 3: Charles’s and Gay-Lussac’s laws
- Investigation 4: Speed and energy (Energy screen)
- Sample data table
- Analysis questions
- Differentiation tips
- Frequently asked questions
- Wrapping up
What students learn
- Gas pressure comes from particles colliding with the container walls.
- Temperature is related to the average kinetic energy of the particles.
- At constant temperature, pressure and volume are inversely related (Boyle’s law).
- At constant pressure, volume increases with temperature (Charles’s law).
- At constant volume, pressure increases with temperature (Gay-Lussac’s law).
Getting started
Search for “Gas Properties” on the PhET website and open the HTML5 version. The simulation has four screens: Ideal, Explore, Energy and Diffusion. Give students five minutes of free play first; they will find the pump handle, the heat-and-cool control under the box and the handle that changes the container width on their own. If you use other PhET labs, the routine will feel familiar, as in our States of Matter simulation lab.
Pre-lab question
Ask: “A sealed bag of chips puffs up when you drive into the mountains. What do you think is happening to the gas inside?” Students write a prediction they will revisit at the end.
Investigation 1: What causes pressure? (Explore screen)
- Pump in one squirt of heavy particles and watch them bounce.
- Turn on the collision counter if available, or simply observe the pressure gauge.
- Add more particles in equal pumps and record the pressure after each.
Students should conclude that more particles means more wall collisions per second and therefore higher pressure.
Investigation 2: Boyle’s law (Ideal screen)
- Set “Hold Constant” to Temperature.
- Add a fixed number of particles and wait for the pressure to settle.
- Use the width handle to make the container smaller in steps, recording the width and pressure each time.
- Calculate pressure × width for each trial.
The product stays roughly constant, which is the signature of an inverse relationship. Have students graph pressure against width and then pressure against 1/width to see the straight line.
Investigation 3: Charles’s and Gay-Lussac’s laws
Constant pressure
Set “Hold Constant” to Pressure ↕ V. Heat the gas in steps and record the temperature and container width. The container expands as the temperature rises.
Constant volume
Set “Hold Constant” to Volume. Heat and cool the gas and record pressure and temperature. Students should notice that the relationship only becomes directly proportional when temperature is measured in kelvins.
Investigation 4: Speed and energy (Energy screen)
Add a mix of heavy and light particles at the same temperature. Students compare the speed histograms and discover that lighter particles move faster on average even though both types have the same average kinetic energy. The Diffusion screen extends this idea by letting two gases mix after a divider is removed.
Sample data table
| Trial | Held constant | Variable changed | Measured result | Pattern |
|---|---|---|---|---|
| 1 | Temperature | Container width (smaller) | Pressure rises | Inverse (Boyle) |
| 2 | Pressure | Temperature (higher) | Width increases | Direct (Charles) |
| 3 | Volume | Temperature (higher) | Pressure rises | Direct (Gay-Lussac) |
| 4 | Volume and temperature | Number of particles | Pressure rises | Direct (Avogadro) |
Analysis questions
- Use the particle model to explain why squeezing a gas increases its pressure.
- Why must temperature be in kelvins for gas law calculations?
- A tire gauge reads higher after a long drive. Which investigation explains this?
- Return to the chip bag. Revise your prediction using evidence from the lab.
For a quick check of understanding, close with one of these exit ticket ideas, or turn the analysis questions into a think-pair-share.
Differentiation tips
- Support: give a partially completed table and sentence frames such as “When ___ increased, ___ increased because ___.”
- Extension: have students derive the combined gas law from their three data sets, or predict a result before running a trial.
- Groups: assign roles such as recorder, operator and checker using our group work roles.
Frequently asked questions
Is the PhET Gas Properties simulation free?
Yes. PhET simulations are free to use and run in a web browser. Students do not need accounts.
How long does this lab take?
Plan one period for investigations 1 and 2 and a second period for investigations 3 and 4 plus analysis. A condensed version covering only Boyle’s and Charles’s laws fits in a single period.
What grade level is this for?
The lab suits high school chemistry and physical science. Middle school classes can use the Explore screen qualitatively without the calculations.
Why don’t my students’ numbers match the gas law exactly?
The simulation shows individual particles, so pressure fluctuates. Have students wait a few seconds and record an average reading.
Wrapping up
Gas laws stop being abstract when students can see every collision. Run the four investigations, have students explain each pattern with the particle model, and they will understand the “why” behind the equations. Browse more free labs on our classroom simulations page, including the Balancing Chemical Equations lab.
