PV=nRT this is the ideal gas eqation . no gas can be an ideal gas. but we use this equation in almost all types of problems. how can we consider some gas as an ideal gas? all gases are real gases,how can we use this eq for real gases? so are we actually using d wrong formula? if this is the case then this gas equation doesnt have any meaning at all.then why are we having such an eq?

Dear ‚ÄčSukanya Roy,

Ideal gases does not exist but few gases like Hydrogen and helium and some what nitrogen behave ideally at high T and low P. 
By considering real gas as ideal (at high T and low P) the different law have been put forwarded and by their combination gas law has been proposed.

The defination ideal gas is based on few points like; gases do not have attraction and repulsion, follow ideal gas equaion at all ranges of T & P, can not be liquified or difficult to liquify. These are the main classes for defining ideal gas. 

So hypothetically the law have been proposed; when the same law has been followed for real gas some error obtained in that formula. 
After that vander waal equation was prepared for the real gas which covered maximum gases. 

Real gases occupy volume and have attraction as well as repulsion between two molecles. 

So the logic is simple if you are getting exact result for your experiment by following real gas equation the gas is ideal & if not then the gas is real. 



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Hi again!

                  The question you arose seems legitimate on first look.Why is this equation used if there are no ideal gases?.Well,the answer is simple and a bit complicated,at the same time.For example,To reach the Model of Atom we are using these days (The Quantum-Mechanical model of the Atom) scientists proposed many models.Somehow,we reached this model which mostly relies on probabilities,like: probability density region where the electron "can be" found.It's because of the Heisenberg Uncertainty principle(but I guess You already know about all of this,right?).So,there's a question! Why don't we exactly locate the electron by some other model? Why can't we have clear-cut image of an atom to which we can point at and say "Hey! This is what an atom looks like!".Well,till this date we haven't reached to that point.There is no other model that arose in the minds of the great scientists because it is as close as we got in about 300-400 years.(But I'm not saying we can't do that).So,We all rely on a "Probable-picture" of atom,which seems theoretical and a really,really good approximation to the real atom to us,doesn't it?But,we still use this model to reach as closest to the picture of the atom as we can,and,guess what,it works too! :) Similarly,there are a lot of cases like that,one of which is the Ideal Gas equation. We got a bit close as to how the real gases behave.The equation is,somewhat,a good approximation to the behaviour of the real gasses.But,still,it has some limitations (So does the quantum mechanical model,but not that much because if we follow it,it only confuses us sometimes).To overcome these limitations,a new equation called "The Van der Walls equation of state" is also proposed,about which,I guess,we'll study later on.

                 So at the end, I guess you'll conclude that this equation is not completely real (Of Course!) and not completely hypothetical.It has certain limitations which The Van der Walls equation overcame.We moved one step ahead! That's how science works.We move one step ahead,and while doing so,we "master" the previous step. We Learn from previous mistakes!

                      I guess that cleared you're doubt.

                                                                                                                                                                                                                                                                                                                                 Hope It helps! :)
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