Gas volume of balloons in liquid nitrogen

55 Gallon Drum Crush implosion

 Unit 2.5 – Charles’ Law 

For Charles’ Law, there is a relationship between temperature and volume, only if the pressure is held constant!

I remember there was this one time when I bought a helium balloon from a store on Valentine’s day. When I took the ballon from the store, it was firm and plump filled with gas, but as I walked to the car with the balloon, the balloon shrunk in size. I then realized that since I live in Canada, the temperature outside was about -25C at the time, and the temperature had a relationship with the volume of the balloon! That was Charles’ Law in action.

Charles’s study on the temperature and volume was also done by Gay-Lussac. But because Gay-Lussac was not as clear as Charles’ in his findings, the relationship was accredited to Charles instead of Gay-Lussac.

Charles’ Law:


Since the equation is displaying a ratio between volume and temperature, the relationship between them is actually directly proportional.  In other words, as the temperature goes up, so does the volume and vice versa.

More than just a math equation

Again, the unique part of this equation is not simply looking at the qualitative observations of how temperature affects volume but the quantitative relationship between the two. The quantitative relationship between temperature and volume now allows scientists or whoever is using the equation to accurate calculate the amount of temperature or volume needed for a particular parameter.

For example: Just like the Helium balloon example, since the balloon was inside at 22C with a volume of 400ml, we can now calculate how much the volume has changed by going outside to -25C mathematically, not just qualitatively!

Why use Kelvin

Whenever we are using these gas law equations, the temperature Unit, Kelvin, must be used. Why is that?

When Charles collected his results, he extrapolated and extended his results and saw that when the volume was equaled to 0ml, it was at -273.15C. The temperature scale, Kelvin, is the absolute zero scale, it is the only one that does not have negative units like in Fahrenheit or Celsius. If we were to use negative temperature scales like Celsius, we would have negative values, ultimately leading to negative volumes, which would not make sense.

This would only make sense since at absolute zero, there is no motion in any of the particles, giving us zero volume.


Here’s a great website from Nasa on Boyle’s Law

Phet’s awesome simulation of gas laws

Gas Properties