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Gas law PV=nrt


The ideal gas law states that

PV = nRT

  • The ideal gas law describes the relationship between pressure, volume, temperature and number of particles.
  • Therefore, regardless of the type of gas, the pressure is always going to be the same if the volume, temperature & number of gas particles are the same.
  • However, identical number of particles does not mean identical mass because molar mass varies with the type of gas. For hydrogen, 1 mole of gas weighs only 1 gram whereas for oxygen, 1 mole weighs 16 grams. 
  • Gas behaves differently from liquid and solid where the mass affects pressure.

What happens when you increase the amount of gas?

  • Well, as you fill the cylinder with more gas, not only the mass increases but the pressure also increases!
  • But the increase in pressure is not caused by the mass, the pressure increase is caused by the number of particles hitting against the walls of the container.


The house analogy

The more people living in a house, the more pressure they will experience!

Pressure is related to moles

  • The pressure of gas is related to the number of moles of gas because moles are related to number of particles.

    Mass is therefore not connected to pressure of gas. It is related to moles.

pressure is related to the number of moles and not mass in a gas