Teach lesson
Gay-Lussac: graphing pressure and temperature
Use real Gay-Lussac data to build a pressure versus absolute temperature graph and interpret the pattern.
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Learning Outcomes
Prepare a graph of pressure versus temperature in kelvin.
Use real rows spread across the run to interpret an approximately linear pattern.
Distinguish an observed relationship from an extrapolation of the ideal model.
Submit a reviewable graph with clear axes, units, and data source.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
What can a graph show?
5 min
A technician must decide whether pressure rises regularly as a rigid container is heated. A list of separate readings does not make the pattern easy to judge: the technician needs a graph that combines reference data with observations from the run. You will build an eight-point graph from five supplied points and three points you observe. The five-point reference list already expresses temperature in kelvin (K = °C + 273.15); in the observation table, convert the display's Celsius readings and round K to one decimal place.
Before building the graph, what direction do you predict for the points as temperature in kelvin increases?
Explain your prediction in one or two sentences. Relate temperature and pressure, or mention that the container keeps a fixed volume.
Collect three points from the run
10 min
Open the lab and take three readings spread across the heating run. Before starting, prepare notes for 00:30, 02:00, and 03:30: at each time, you will record temperature in °C and pressure in kPa. You will then combine them with five reference points from the same run.
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. Then convert each temperature to K and round to one decimal place.
| Run time (min:s) | Temperature °C | Pressure kPa | Temperature K |
|---|---|---|---|
The table is also graded. After completing it, use this format: Lowest: time ___, T = ___ K. Highest: time ___, T = ___ K. Those elapsed times will identify your points on the graph.
Five reference points
- Point A: T = 297.0 K; P = 87.76 kPa.
- Point B: T = 300.9 K; P = 88.98 kPa.
- Point C: T = 308.0 K; P = 91.36 kPa.
- Point D: T = 312.6 K; P = 93.10 kPa.
- Point E: T = 317.8 K; P = 95.48 kPa.
Build, check, and submit your graph
25 min
Use a spreadsheet and follow this route:
1. Create three columns: T (K), Reference P (kPa), and Observed P (kPa).
2. In the first five data rows below the headings, copy reference T and P into the first two columns; leave the third blank.
3. In the next three data rows, copy your observed T into the first column and their P into the third; leave the second blank.
4. Select all three columns and insert an XY scatter graph. Google Sheets and other spreadsheets will create two series with one shared temperature column.
5. Keep T on the horizontal axis and P on the vertical axis. Use a different style for each series and a legend naming reference points and lab observations. Add units and a numerical scale covering all eight points.
6. Aim to build and format the graph in 15 minutes, use 5 to check it with the following fields, and reserve 5 to export and attach the file.
Axis template
The image does not show the answer. Use it to check axes and units; you add the scale and points in your submission.
Direction. As you move toward higher temperatures, what do the pressure points do overall?
Shape. Which description best fits the points within the displayed interval?
Isolated points. Which description matches your graph?
Write one sentence explaining why you described the shape as straight, curved, or without a pattern. Use the placement of the points as evidence.
After seeing the graph, what do you do with your initial prediction?
Your pressure-temperature graph
Attach the PDF or spreadsheet file. The graph must show pressure on the vertical axis, temperature in kelvin on the horizontal axis, units, a numerical scale, the five supplied points, and your three observations in a different style with a legend identifying both sets.
File check. Which description matches the graph you just attached?
Interpret without overstating
10 min
A good graph does more than say whether something rises. It also helps decide how much we can claim.
Claim. In two sentences, state the relationship shown between pressure and temperature and limit the claim to the approximate displayed interval.
Why must gas amount and volume stay fixed when studying the relationship between P and T?
Limitation. Name one specific limitation of the work and explain how it reduces what you can conclude from the graph.
To analyze temperatures far beyond the data, use this foundation: the ideal model states absolute pressure / T(K) = constant when amount and volume are fixed. Decide whether the measured interval tests a prediction near 0 K and what could change in a real substance.
Extrapolation. Do the data from 297 K to 318 K test what happens near 0 K?
In one or two sentences, state what the ideal model predicts for absolute pressure near 0 K and explain why real ethanol or the narrow measured interval may prevent testing it.