Upper secondary · 10 min

Gas in a piston: pressure, volume, temperature

Squeeze and heat a gas made of moving particles and see why PV = nRT holds.

Goal

Test Boyle’s and Gay-Lussac’s laws and connect them to the motion of particles.

Apparatus and reagents

A cylinder with a movable piston containing an ideal gas; a thermometer and a pressure gauge.

Procedure

At T = 300 K and n = 1 mol, move V from 10 L to 5 L. Note the pressure.
Return to V = 10 L and raise T from 300 K to 600 K.
Double the amount of gas at fixed T and V.

What to observe

Halving V doubles P (2.49 → 4.99 bar); doubling T doubles P; doubling n doubles P.
Particles move faster when T is higher (speed grows like √T) and hit the walls more often when V is smaller.

Explanation

Pressure comes from countless collisions with the walls. A smaller volume means more collisions per second, so $P \propto 1/V$ at fixed $T$ and $n$ . A higher temperature means faster particles that hit harder and more often, so $P \propto T$ at fixed $V$ ; more particles means more collisions, so $P \propto n$ . Together: $PV = nRT$ . The displayed pressure comes from this law, and the particles illustrate it: they do not collide with each other, as in an ideal gas.

History of the experiment

Robert Boyle trapped air in a J-shaped tube in 1662 and found that pressure and volume move in opposite directions — the first quantitative gas law. Gay-Lussac and Charles then showed that heated gases expand in strict proportion to absolute temperature, and Avogadro added the missing variable: the particle count

n

. Clapeyron fused the results into

PV = nRT

in 1834, the same law the piston in this simulation obeys.

Chemists behind it

Robert Boyle Joseph Louis Gay-Lussac Amedeo Avogadro