Teach lesson
Gay-Lussac: does pressure rise when gas is heated?
Observe a real Gay-Lussac run and use a few data rows to decide how pressure changes when a fixed-volume gas is heated.
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Learning Outcomes
Observe the Gay-Lussac remote run and describe how pressure and temperature change together.
Use 4 real data rows to support a qualitative claim.
Distinguish an evidence-based conclusion from an initial prediction.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
First, picture the gas inside the container
8 min
Warnings not to heat closed containers begin with a concrete physics question: if the volume cannot expand, what happens to gas pressure as temperature rises? You will not test a consumer product here; you will investigate that question with a controlled remote run. When gas is trapped in a rigid container, its particles hit the walls. To interpret the readings, you will begin with a simplified model that assumes a fixed amount of gas at fixed volume; at the end, you will check the limit of that assumption for an ethanol sample.
The real lab setup
The run heats an ethanol sample in a fixed-volume container and shows pressure and temperature during heating.
Before looking at the data, what do you predict will happen to pressure as temperature increases?
The container is rigid: its volume does not change during the run. This prevents expansion or compression of the container from introducing another cause of pressure change.
Explain in one or two sentences why you chose that prediction, taking into account that volume stays fixed.
Observe the real run
12 min
Open the lab from this activity and make one observation of the fixed-volume ethanol sample. Before starting, prepare two notes: near 00:30 and 03:30, you will record temperature in °C and pressure in kPa.
Open the Gay-Lussac lab
The sealed sample always contains the same total amount of ethanol, and the container keeps a fixed volume. The ideal model also treats the gas-phase amount as fixed; the lab records temperature and pressure, not the amount in each phase.
Open the lab from this activity's lab button.
On the configuration screen, select the only available sample: 0.014 mol of ethanol.
Start one observation, which takes about 4 minutes. During the run, record approximate temperature and pressure at the times shown in the following table.
Return to TEACH and complete that table before continuing with the analysis.
Lab readings
The times are already provided. Copy observed readings into the °C and kPa columns. Units appear in the headings.
| Run time (min:s) | Temperature °C | Pressure kPa |
|---|---|---|
Compare the endpoints of the heating run
8 min
The following two data points show the beginning and end of the reference run. Temperature is in degrees Celsius and pressure is in kPa. Use them to calculate the change between both measurements.
Reference data
- Measurement 1: T = 23.9 °C; P = 87.76 kPa.
- Measurement 61: T = 44.6 °C; P = 95.48 kPa.
Calculate the changes. Write ΔT = final T − initial T and ΔP = final P − initial P, both with units.
Comparing the beginning and end, how do temperature and pressure change?
What do you do with your initial prediction after reviewing the data?
Build a conclusion with limits
8 min
You do not need to prove the whole Gay-Lussac law. Complete four short steps: claim with evidence, particle explanation, model scope, and application limit. For the particle model, you may use these keywords: temperature, motion, collisions, walls, and fixed volume.
The total amount of ethanol in the sample stays fixed, but ethanol can be distributed between liquid and gas phases during heating.
Claim and evidence. In two sentences, state what happened to pressure and support it with both complete temperature-pressure pairs recorded at 00:30 and 03:30.
Reasoning. In one or two sentences, connect heating, particle motion, collisions with the walls, and fixed volume.
Model scope. Use the possible distribution between phases to explain why the run does not demonstrate that the particle model is the only possible explanation of the trend.
Application limit. Explain why this activity cannot calculate the failure temperature or pressure of a real container. Name one container property that was not tested.