Thermodynamics
Isothermal compression
Compress at constant T: ΔU = 0, so Q = W.
Isothermal compression — interactive Thermodynamics simulation. Compress at constant T: ΔU = 0, so Q = W. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Isothermal process
Compress at constant T: ΔU = 0, so Q = W.
During an isothermal process the internal energy of an ideal gas depends only on temperature, so ΔU = 0. Any work done on the gas must leave as heat to the reservoir. Watch the P–V curve follow PV = constant as the piston moves.
- ΔU = 0
- Q = W
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
A gas is compressed to a smaller volume while its temperature is held constant (isothermal). Is more work required to compress it further?
Predictions to weigh
- Compressing to a smaller final volume requires less work.
- Compressing to a smaller final volume requires more work (a more negative Wgas).
- The work needed is the same no matter the final volume.
Variable roles
What you set:
- Final volume V₂ (L)
What you measure:
- Work done by gas W_gas (J)
How the investigation runs
- Open the isothermal-compression preset and press Reset. 1 mol of gas starts at 49.9 L, 300 K.
- Enable the work-done-on-gas readout.
- Set the target (final) volume for each trial and record the work done by the gas.
Governing equation
First Law of Thermodynamics — ΔU = Q − W
Internal energy change equals heat added minus work done by the gas: ΔU = Q − W. For an isothermal ideal-gas process, ΔU = 0, so all the work done on the gas leaves as heat.
What the printable worksheet asks students to work out
- For one trial, compute W_gas = nRT·ln(V₂/V₁) using n = 1 mol, R = 8.314 J/(mol·K), T = 300 K. Compare to the table.
- W_gas is negative in every trial. Explain what a negative value means physically for a gas being compressed, and why compressing to a smaller V₂ makes W_gas more negative.
Where this shows up beyond the lab
- Since ΔU = 0 for any isothermal process (temperature doesn't change), the first law says Q = W_gas here too. Is heat flowing into or out of the gas during this compression? Explain using your sign convention.
- To keep the gas at constant temperature while compressing it, real experiments need a heat reservoir in contact with the cylinder. Explain why compression would heat the gas up if that reservoir weren't there.
- AP Physics 2 — Unit 9: Thermodynamics
- IB Physics — B.4 Thermodynamics
- General High School Physics — Heat, temperature & gas laws
- NGSS High School Physics — Thermal energy transfer
- Welcome to Isothermal Compression
- Select the chamber
- Press Play
- Compression at constant T
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.