Gay-Lussac's Law: Pressure and Temperature

A sealed, rigid vessel holds a fixed amount of gas. Its walls never move, so the volume is fixed — and at fixed volume the absolute pressure of an ideal gas is proportional to its absolute temperature: P1/T1 = P2/T2, with every temperature in kelvin. Set the pressure and temperature at which the vessel was sealed, then change the temperature and watch the gauge needle, the molecules and the point on the pressure-against-temperature line move. The line is straight, and it runs back to zero pressure at −273.15 °C — which is how the kelvin scale was inferred in the first place. The volume never changes; that is the whole lesson.

Change since sealing+0.0 kPa
Percentage change+0.0 %
Mean molecular speed1.000×
Absolute zero-273.15 °C
where this line reaches zero pressure (0 K)

WhySame temperature, same molecular speed, same pressure: nothing to see until you move the temperature.

What the reading meansNothing has changed yet — move the temperature slider and watch the gauge, not the walls.

Fixed by the physics: absolute zero -273.15 °C (0 K) · standard atmosphere 101.325 kPa · 1 bar = 100 kPa · 1 psi = 6.894757 kPa. The gauge reading uses the STANDARD atmosphere, which is not the same as the local atmospheric pressure where you are.
Tip: load the car tyre, then drop the current temperature to -5 °C. The gauge falls from 259.7 kPa to 203.0 kPa without a molecule leaking out — which is why tyre pressures are specified cold.
Pressure now  P2 = P1 T2 / T1
101.3 kPa
= 1.013 bar · 14.69 psi
Gauge pressure
0.0 kPa
= 0.0 psi gauge
Pressure ratio
1.000
= T2 / T1 = 293.15 K / 293.15 K
The constant  P / T
0.3456 kPa/K
P divided by T: the same before and after
Sealed pressure101.3 kPa
= 0.0 kPa gauge · 0.0 psi
Sealing temperature20 °C
in kelvin: 293.15 K
Current temperature20 °C
in kelvin: 293.15 K
Load a sealed container
custom setup