Gas Laws

Summary

The basic gas law relationships …
- The pressure of a gas is inversely proportional to its volume when temperature is constant.
  - This relationship is known as Boyle's law or Mariotte's law.
- The volume of a gas is directly proportional to its temperature when pressure is constant.
  - This relationship is known as Charles' law or Gay-Lussac's law.
- The pressure of a gas is directly proportional to its temperature when volume is constant.
  - This relationship is not associated with any particular scientist.

Combine these relationships into one law, which can be written in two different ways …


functional thermodynamics version			statistical thermodynamics version
PV = nRT			PV = NkT
where …
P =	absolute pressure
T =	absolute temperature
V =	volume
and …			or …
n =	number of moles		N =	number of particles
R =	gas constant = 8.315 J/mol K		k =	Boltzmann's constant = 1.382 J/K

Thermodynamic changes with special names …
- An isobaric process is one that takes place without any change in pressure.
- An isochoric process is one that takes place without any change in volume.
- An isothermal process is one that takes place without any change in temperature.
  - Isothermal processes are often described as "slow".
  - The pressure of a gas is inversely proportional to its volume only if the change takes place isothermally.
- An adiabatic process is one that takes place without any exchange of heat.
  - Adiabatic processes are often described as "fast".
  - The pressure of a gas is not inversely proportional to its volume if the change takes place adiabatically.

The Physics Hypertextbook

No condition is permanent.

© 1998–2012 Glenn Elert