Charles' Law (Volume and temperature relationship, P constant)
In this law, we will look at how Volume and Temperature are related for a fixed mass of gas in a sealed container.
In the above diagram, a fixed mass of gas within a piston is heated. As the temperature of the gas increases, the volume increases, pushing the piston upwards.
If we plot a graph of volume against temperature for the piston above we would generate the graph below:-
As can be seen from the graph above, when plotted using the Celsius scale, a proportional graph is generated. However, this graph is not directly proportional (doubling temperature does not double volume).
If the intercept on the x axis is found, however, it is shown to be the same value no matter the gas - absolute zero:-
Therefore, in order to generate a directly proportional graph, the Kelvin scale must be used:-
This graph does follow a linear relationship, which shows that:-
T1 = Temperature at start.
The video below gives a short summary of Charles' Law:-
A weather balloon is held at a constant pressure of 1 atmosphere before launch, with a volume of 4 m3. The temperature of the balloon when first inflated was 12 °C. By the time of launch the balloon's temperature had increased to 28 °C, what is the new volume of the balloon?
T1 = 12 °C = 12 + 273 = 285 K
T2 = 28 °C = 28 + 273 = 301 K
Kinetic Theory Explanation of Charles' Law
1. The gas particles have greater Kinetic Energy.
2. The particles will collide with the container walls more often.
3. Higher rate of collisions gives a larger Force applied to the walls.
4. Larger force pushes out the walls of the container giving a bigger volume.