Ideal Gases (Cambridge (CIE) A Level Physics): Revision Note

Ideal gases

• An ideal gas is one which obeys the relation:

$pV\propto T$

• Where:

  • p = pressure of the gas (Pa)

  • V = volume of the gas (m³)

  • T = thermodynamic temperature (K)

• According to the relation:

  • temperature is directly proportional to pressure, for a constant volume

  • temperature is directly proportional to volume, for a constant pressure

  • pressure and volume are inversely proportional to each other, for a constant temperature

Temperature and pressure

• For a constant volume

• When the temperature of a gas is increased

• Then the pressure is also increased

  • the molecules have a higher kinetic energy

  • so move about more and collide more with the walls of their container

  • creating more pressure

Temperature and volume

• For a constant pressure

• When the temperature of a gas is increased

• The volume is also increased

  • the molecules have a higher kinetic energy

  • so move about more and move further apart from each other

  • expanding to create a bigger volume

Pressure and volume

• For a constant temperature

• An increase in pressure comes from a decrease in volume

• The smaller container creates a smaller surface area

• There are more collisions which creates more pressure