van der waal equation

[superduper12]

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So here is the van der waal equation for real gases

P = (nRT)/(V-nb) - (an^2)/V^2

So suppose we double by number of moles in a container by PV = nRT the pressure would double. BUT this could cause more molecules closer together and thus increase the intermolecular force/attraction. So the pressure wouldn't completely double. That's why this is subtracted (an^2)/V^2 which represents the intermolecular attraction.

Now I don't understand why we substract nb from V?

b/c if real volume is greater than ideal volume, shouldn't we add do V + nb?

 

[niranjan162]

the -nb is due to the actual gas molecules having volume in themselves which takes away from volume that they have to move. where b is a constant associated with whatever type of gas it is.

i wouldnt worry to much about memorizing everything about this equation as it will def be given in a passage. but understanding it cant hurt.