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## 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.