Pressure & Temperature in Gases (Cambridge International IGCSE Chemistry)

Spec point — 1.1.3 · Describe the effects of temperature and pressure on the volume of a gas

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

Spec point — 1.1.3 · Explain, in terms of kinetic particle theory, the effects of temperature and pressure on the volume of a gas

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!

Exam Hint If you are talking about the particles, then make sure that you talk about them spreading out.

If you are talking about the material, then you can use the word expand.

You will lose a mark in an exam if you talk about particles expanding!

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