Pressure law or Gay Lussac’s Law

The behaviour of gases at constant volume when the pressure changes with respect to its absolute temperature is described in Gay-Lussac’s Law

Gay-Lussac’s Law or Pressure Law states that the pressure of a fixed mass of a gas at constant volume is directly proportional to its absolute temperature.

Mathematically,

Pressure P   Absolute temperature T

P    T

P=KT

Therefore,

Where   are the initial pressure and temperature respectively.

   are the final pressure and temperature respectively.

 Proof of Pressure Law

The bulb C is totally immersed in water . the flame is used to increase the temperature of the water so that the temperature of the gas in C  increases. The pressure gauge indicate the pressure of the gas while the thermometer read out the temperature.

As the temperature increases the pressure increases . The different reading of the thermometer and the corresponding readings of the pressure gauge were recorded simultaneously up to 10 times.

The graph of pressure is plotted against temperature. A straight line graph is obtained.

Precautions

1. The air and the bulb must be dry
2. The thermometer must be kept upright
3. The reading of the pressure gauge must be taken without error due to parallax

Example

The pressure of a gas at  is 200cmHg. Calculate the pressure at   with same volume.

Solution

=20+273 = 293K

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