Introduction to Dalton’s law of partial pressures 

As per Dalton’s law, we understand the relationship between two gases in a container. 

Dalton’s law of partial pressures has a lot of applications.It is one of the most conventional methods to measure the pressure exerted by two gases and calculate the partial and total pressures.

With the help of this law, we understand that pressure in a container consisting of a mixture of gases could be found by calculating the sum of partial pressures of each of these gases. 

The partial pressure between these gases is exerted individually only when they occupy the volume of the mixture at the same temperature. 

So we can say Dalton’s law allows us to find the pressure exerted by two gases in a container.

While you are asking your local tire shop owner to check the pressure of your tires, have you ever thought about what he does? You might have noticed that they use a tire gauge to measure the pressure in the tube of your tire.

Why exactly?

Because it helps them measure and adjust the physical properties of a large number of gases in our tires and maintain the right pressure, that’s not possible to tell by some other method. 

On this kind of molecular level, the pressure that we are measuring comes from the force of the individual gas molecules that collide with other objects (in this case, the walls of the tube of the tire.) This is where Dalton’s law of partial pressures is implemented.

John Dalton, an English chemist, stated “Dalton’s law of partial pressure”. 

Dalton’s law (or Dalton’s law of partial pressure) has been adopted as the universal method to calculate the partial and the total pressure of gases.

Dalton’s law also doesn’t assume any chemical interaction between the component gases. 

So let’s understand the explanation of Dalton’s law of partial pressure in detail.

The Partial Pressure of a gas

The entire thought about this theory occurred to John Dalton when he was on vacation, and the weather was too humid. This made him question the humidity and the particles in the air.

In this observation, he realised that each gas has a distinct behaviour in a mixture of gases. The observation could be summarised in the following statement –

If there’s a container that contains 10 Nitrogen molecules, they will exist independently. If we were to add 10 oxygen molecules to this container, the pressure would increase to 20 mmHg. Now, if we were to remove 5 molecules of oxygen from this container, we would have 10 Nitrogen molecules and 5 oxygen molecules, and the pressure would decrease to 15 mmHg.

Even though the number of particles is changed, every particle will still fly around and hit the walls of the container, contributing individually to the pressure of the container yet not interfering with other particles at all. This means the more gas particles there are in a container, the higher the pressure is in that container. At the same time, the lower particles, the lower pressure. 

The individual pressure from both these gases refers to partial pressure.

What is Dalton’s law of partial pressures – An explanation

As Dalton understood partial pressures, the phenomenon was named after him. 

According to the law of Dalton, we can conclude that a mixture filled with multiple gases exert partial pressures on each other. The total pressure equals the sum of partial pressures that each gas exerts.

This fundamental could also be illustrated with a figure.