Adivision of "YIDYARTHIACADEMY PVT' LTD'" JEE & NEETReal Gases OEB Rr.lJn Ll eHATTEBJ E

1. Real gases deviate &om ideal gas behaviour because1 . Real gases molecules have a finite volume. (since on liquification real gases occupy a finitevolume)2. Inter molecular atraction force betneen real gas molecules is not zero. (Real gases can beconverted into liquid whereas ideal gases can't be )Deviation of real gases from ideal behaviour can be measured by using comperessibiliry factor

(PV)real * (PV,,)real =

(1. -)lr!L(z). z- (PV)ideal RT (V,,,)ideal

V-- volume of one mole ormolar volume.Variation ofZ with pressurc atconstant temperature

'Ht/Co2 9^o1d":i:*:N2 (i)Z:1 for ideal gas(rl)Z> I at all pressures for He/FI,

(iii)Z < 1 at low pressure (for all other gases)(ir)Z > I at high pressere (for all other gases).Z=l

He I I{,itleal

P

VanderWall Equation of Real Gases -The ideal gas equation does not consider rhe eff'ect of attractive forces and firrite molecularvolume. Vander *'aal corrected the ideal gas equation by taking the effect of(a) Molecularvloume(A) Volume Correction

(h) Molecular atffaction.

Ideal gas equation: PV, = nRTHere V. stands for the volume which is available for &ee mor,ement of the molecules or V,

is the volume ofthe containerbecause molecules are assumedto be point masses. But for a real gas Vr * voiume ofcontaimer beacuse molecules have a finite volurne andhence complete volume of container is not available forfree movement of molecules.The r,'olune that is not available

for free movement is called exclude d volumc. It is caiculatedasfollows:For molecule 2, the entire shaded region is excluded, as its cenlre of mass cannot entre thisregion. Ifboth molecules nere ideal then they would not have experierced any excluded volumebut this is not in the case of a real gas as the centre of mass of molecule 2 cannot entre theshaded region.Hence for the pair of real gas molecules ( 1 &2) as shou'n above.

Excruded volumepermolecule : !{!"r'"f} = -{i -'}b: excludedvolume permode of gas:For n moles excluded volume : nb

N ^4(+*,)

W = V - "blvolume

correction .

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