Gas Laws

Charles Law:

Charles’s Law states that, at constant pressure, the volume of a gas is directly proportional to its absolute temperature. 

Imagine a balloon being warmed up. As the air molecules inside gain heat energy, they move faster and collide more frequently with the balloon’s walls. This increased molecular activity results in the balloon expanding or inflating. Conversely, if the balloon is cooled, the molecules lose energy, move slower, and collide less frequently, causing the balloon to deflate. 

The term “absolute temperature” refers to temperature measured on the Kelvin scale, where absolute zero, the lowest possible temperature, is 0 K. In Charles’s Law, this Kelvin scale is crucial. According to the law, if you double the absolute temperature of a gas, its volume will also double, provided the pressure remains constant. 

In the context of Charles’s Law, the Kelvin scale is indispensable for understanding the relationship between absolute temperature and the volume of a gas. Absolute zero, denoted as 0 K on the Kelvin scale, is considered the lowest achievable temperature, at which molecular motion theoretically ceases. This reference point allows scientists to quantify temperatures without any negative values, making it a more consistent and comprehensive scale for thermodynamic studies. 

Now, let’s delve into the specifics of Charles’s Law. The law states that, at constant pressure, the volume of a gas is directly proportional to its absolute temperature. This proportionality is a key aspect of the law and can be expressed mathematically as 

 V ∝ T or V/T = constant 

where V is the volume and T is the absolute temperature.

In the given diagram, we can take multiple readings by keeping the pressure constant. The initial reading can be  ​V1 and T1 ​ representing the initial volume and temperature respectively, and then we can take a final reading as   V2 ​ and T2​ representing the final volume and temperature respectively.

Since their ratios are supposed to be constant, so we can say that

V1⁄T1=V2⁄T2 ​

This relationship helps us understand how gases respond to changes in temperature, providing a fundamental principle in the study of thermodynamics and the behaviour of matter.

A Change of Temperature at Constant Volume: 

Increasing temperature causes gas molecules to gain kinetic energy, leading to faster and more frequent collisions with the container walls. This increased collision frequency results in higher pressure. 

A Change of Volume at Constant Temperature: 

Decreasing volume confines gas molecules into a smaller space, causing them to collide more frequently with the container walls, resulting in higher pressure. Conversely, increasing volume reduces collision frequency and lowers pressure.