Disclaimer: Due to unforeseen difficulties, we have had to take down the images on this notes page. They will be replaced shortly. We apologise for the inconvenience, but hope that the new images will provide you with an even better learning experience.


  1. Relate the change in volume of a gas to change in pressure applied to the gas at constant temperature and use the equation PV = constant at constant temperature.

When volume increases at a constant temperature, the gas molecules have to travel further to collide with the surface of the container. Therefore, there are fewer collisions, and thus the pressure the gas exerts on the surface of the container is less.

On the other hand, when we reduce the volume at a constant temperature, the gas molecules will collide with the container surface more frequently, increasing the pressure.

In equation form, this is represented as PV = k,

Where P is pressure in Pascals (Pa), V is volume in m3 and k is a constant.

The constant k changes according to the gas, so if the exam question doesn’t provide you with a value for k, you’ll have to calculate it using P and V. Always make sure the units are correct.

Note that this equation is only valid when the temperature and the number of moles of gas in the container is kept constant.



Notes submitted by Sarah.

Click here to go to the next topic.

Click here to go to the previous topic.

Click here to go back to the Science menu.