Pressure & Temperature in Gases (Cambridge (CIE) IGCSE Chemistry)

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 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

Pressure increases as volume decreases in a bicycle pump

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

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

Gases & kinetic theory

Extended tier only

• Gaseous particles are in constant and random motion

• The pressure that a 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

How does temperature affect the volume of a gas?

• Increasing the temperature increases the kinetic energy of each particle

  • Remember: The thermal energy from increasing the temperature is converted to kinetic energy in the particles

• As the temperature increases, the particles in the gas move faster and spread out more

• If the gas particles are inside a container, they will collide with the container 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!

How does pressure affect the volume of a gas?

• Pressure is about the number of particles in a given volume

• Increasing the pressure means that there are the same number of particles but in a smaller volume

  • Conversely, decreasing the pressure means that there are the same number of particles but in a larger volume

When the pressure increases, the volume decreases. This means that the molecules collide with the container walls more frequently 

• Since the volume is decreased, the gas particles hit the container walls more frequently

  • If the pressure is too high, this can result in the container leaking gas or exploding