Thermodynamics
Adiabatic expansion
Expand with no heat exchange: the gas cools.
Adiabatic expansion — interactive Thermodynamics simulation. Expand with no heat exchange: the gas cools. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Adiabatic expansion
Expand with no heat exchange: the gas cools.
In an adiabatic process Q = 0, so expansion work drains internal energy from the gas. Molecules slow down, temperature drops, and the P–V path is steeper than an isotherm because no heat enters to sustain pressure.
- Q = 0
- TV^(γ−1) = const
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 expands quickly, with no time to exchange heat with its surroundings (adiabatic). Does the gas's temperature change even though no heat enters or leaves?
Predictions to weigh
- The gas cools down — it does work on its surroundings using its own internal energy.
- The temperature stays the same, since no heat is exchanged.
- The gas heats up as it expands.
Variable roles
What you set:
- Final volume V₂ (L)
What you measure:
- Work done by gas W_gas (J)
- Final temperature T₂ (K)
How the investigation runs
- Open the adiabatic-expansion preset and press Reset. 1 mol of diatomic nitrogen (f = 5) starts at 24.9 L, 300 K.
- Enable the final-temperature readout on the chamber.
- Set the target (final) volume for each trial, and record the final temperature and the work done.
Governing equation
Adiabatic Process — ΔU = Q − W
With no heat exchanged (Q = 0), the first law reduces to ΔU = −W_gas: an expanding gas can only do work by spending its own internal energy, so it must cool. Pressure and volume follow P·V^γ = constant.
What the printable worksheet asks students to work out
- For one trial, compute T₂ = T₁·(V₁/V₂)^(γ−1) using γ = (f+2)/f = 1.4, T₁ = 300 K, V₁ = 24.9 L. Then compute W_gas = −ΔU = −(f/2)nR(T₂ − T₁). Compare both to the table.
- With Q = 0 in every trial, the first law gives ΔU = −W_gas exactly. Explain, in terms of energy conservation, why an expanding gas that does positive work must cool down when it can't draw in heat.
Where this shows up beyond the lab
- An aerosol spray can feels cold as gas rushes out and expands rapidly — too fast to exchange much heat with the surroundings. Explain why this is a real-world (if imperfect) example of adiabatic cooling.
- Compare your final temperatures here to what isothermal-compression's reverse (an isothermal expansion) would give for the same volume change: isothermal keeps T constant, but this adiabatic case doesn't. Why does removing the heat-exchange assumption change the outcome?
- 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 Adiabatic Expansion
- Select the chamber
- Press Play
- Expansion with no heat flow
- 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.