Do I need to install anything?

No. It runs in any modern browser, free, with no account required.

For Students · Entropy

Entropy for a plastic bottle

Built for students learning it for a class or exam. See the concept move instead of memorizing formulas — and check your homework intuition. Simulate a plastic bottle live below — adjust the inputs and watch it respond, right in your browser.

Entropy & Free ExpansionLive

the second law in action

Controls

Speed1×

Gas confined to one half rushes to fill the whole box the instant the partition is removed — and never spontaneously crowds back. That irreversibility is the second law: entropy, a measure of disorder, always increases. For doubling the volume the entropy rises by nR·ln2, purely because there are vastly more ways to be spread out than packed in.

▶ Run in Python

Data Inspector

Fraction on left100%

ΔS (per mole)0.00 J/K

Stateconfined

Governing equation

Δ S = n R ln \frac{V _{f}}{V _{i}} = R ln 2 = 0.00 J/K

Reading this result: All 120 particles are trapped in the left half — entropy is at its lowest. Remove the partition to watch it climb.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

or unlock everything with Pro →

Also for:Researchers Educators Engineers Hobbyists & Makers K-12 Students First Responders General version →

More with Entropy

Entropy for a steel beam Entropy for an aluminum frame Entropy for a concrete mix Entropy for a carbon-fiber panel Entropy for a rubber seal Entropy for a glass pane Entropy for a copper wire Entropy for a titanium implant

Frequently asked questions

Is this good for students?: Yes — this version of "Entropy for a plastic bottle" is framed for students learning it for a class or exam. See the concept move instead of memorizing formulas — and check your homework intuition.
Do I need to install anything?: No. It runs in any modern browser, free, with no account required.