Pressure & Temperature in Gases (Cambridge (CIE) O Level Chemistry): Revision Note

Pressure & Temperature in Gases

• A change in temperature or pressure affects the volume of gases

• As the air inside a hot air balloon is heated up, it expands and the balloon gets bigger

• This is because the volume of a gas increases as its temperature increases

As temperature increases gas volume increases. The density decreases as the volume increases so the balloon rises.

• If you have a gas stored inside a container that is squeezed, the pressure increases as you decrease the volume

• This is what happens in a bicycle pump

• As you compress the bicycle pump the high pressure allows you to inflate a tire

• You can feel the force of the high pressure if you put your finger on the end of the pump

Pressure increases as volume decreases in a bicycle pump

Kinetic Theory 

• Gaseous particles are in constant and random motion

• The pressure that gas creates inside a closed container is produced by the gaseous particles hitting the inside walls of the container

Moving particles of gas colliding with each other and the container walls

• An increase in temperature increases the kinetic energy of each particle, as the heat energy is transformed to kinetic energy, so they move faster

• As the temperature increases, the particles in the gas move faster, impacting the container's walls more frequently

• If the container walls are flexible and stretchy then the container will get bigger and bigger, just like the hot air balloon!

• If the container is made smaller, then the gas particles hit the wall more frequently

• So when there is a decrease in volume this causes an increase in gas pressure

Molecules collide more frequently with the container walls when the pressure is increased