4.0 moles of argon and 5.0 moles of PCl5 are introduced into an evacuated flask of 100 litre capacity at 610K. The system is allowed to equilibrate. At equilibrium, the total pressure of mixture was found to be 6.0‌atm. The Kp for the reaction is [Given : .R=0.082L‌atm‌K−1‌mol−1]
Here 4 moles of inert gas argon also present. ∴ Total moles of mixture present at equilibrium, nT=5+x+4 =9+x At equilibrium, total pressure (pT)=6‌atm Volume (v)=100L Temperature =610K ∴ using ideal gas equation, PTV=nTRT ⇒6×100=(9+x)×0.082×610 ⇒x=3 Now, KP=‌
PPCl3×PCl2
PPCl5
=‌
[
3
9+3
×6]×[
3
9+3
×6]
[‌
5
9+3
×6]
=‌
27
12
=‌
9
4
=2.25‌atm Note : Inert gas always contribute to total mole and pressure calculation.