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Why is van der waal constant 'b' not excluded for hydrogen and helium even if their gas molecules are extensively small?

Why is van der waal constant 'b' not excluded for hydrogen and helium even if their gas molecules are extensively small?

Grade:11

3 Answers

Shivangi Khatter
askIITians Faculty 468 Points
5 years ago
because it will still have some volume. may it be very less
Susmita
425 Points
5 years ago
You may have heard about liquification--like liquification of petrolium gas so that you get LPG.In the same process H,He,CO2 can be liquified.
When you apply high pressure on a gas,ie,compress it,its volume reduces.But you can never make V=0,no matter how high pressure you apply.Because gas molecules of a real gas are incompressible,they have a finite size,say size of atoms.Atoms cannot be compressed.b is that finite volume.So even if you can neglect b at low pressure but you cannot neglect it at high pressure.
It is very important in liquification process.There is a certain temperature T=3b above which you cannot liquify a gas no matter how high pressure you apply.
 
Susmita
425 Points
5 years ago
Sorry that T=8a/27Rb.
........................................................................................hope the previous answer helps.
 

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