Why Do We Add Constants in the Van der Waals Equation?

[jd12345]

In reality pressure of a gas is lower than what is expected and volume is larger than expected - as ideal gas equation neglected volume of gas molecules and forces between them. Van der waal corrected it but:-

I need to know then why do we add the constant n^2a/V^2 in pressure and subtract nb in volume


Shouldnt we subtract n^2a/V^2 from pressure as it is lower than what was expected

similarly we should add nb in volume as it is more than what was expected

Im a bit confused over van der waal's equation. Cannot understand it

 

[Zefram]

.
Thank you for bringing up this interesting question about the Van der Waals equation. As you have correctly pointed out, the ideal gas equation does not take into account the volume of gas molecules and the attractive forces between them, resulting in a lower pressure and larger volume than expected in real gases.

To correct for this, the Van der Waals equation introduces two correction terms: n^2a/V^2 in the pressure term and nb in the volume term. Let's take a closer look at these terms and their effects on the equation.

The term n^2a/V^2 is known as the Van der Waals constant for pressure and it takes into account the attractive forces between gas molecules. This term is added to the ideal gas pressure term, resulting in a higher pressure than expected. This makes sense because the attractive forces between gas molecules would cause them to come closer together and therefore increase the pressure.

On the other hand, the term nb is known as the Van der Waals constant for volume and it takes into account the volume of gas molecules. This term is subtracted from the ideal gas volume term, resulting in a lower volume than expected. This is because the volume of gas molecules themselves would take up space and therefore decrease the overall volume of the gas.

In summary, the Van der Waals equation accounts for both the attractive forces between gas molecules and the volume of the molecules themselves, resulting in a more accurate representation of real gases. This is why the correction terms are added to the pressure term and subtracted from the volume term.

I hope this helps clarify your confusion about the Van der Waals equation. Keep asking questions and exploring the world of science!