We have to use Dalton's law of partial pressures which states that in a mixture of gases each gas will exert its partial pressure corresponding to its molar fraction

In this case mixture consists of hydrogen4moles,helium 3 moles and krypton 2 moles packed in a cylinder of 9 litres and total pressure is 13atm

So partial pressure due to krypton is its mole fraction multiplied by total pressure

As krypton mole fraction is 2/9 its partial pressure is 2/9x13=26/9 atm=2.8888 atm

Now if we introduce 4 moles of xenon into the present system as vol and temperature are fixed

it will result in increase in total pressure corresponding to the moles added.

As the number of moles added are 4,the total moles increases from 9 to 13 and the total pressure in the cylinder will be

13X13/9=169/9 ATM

pkr= its changed mole fraction xchanged total pressure

=(2/13)x(169/9)=26/9 atm =2.8888atm

so it remains unchanged even if xenon is added

Now if we introduce 2 moles of krypton into the system without any change of temperature and volume

The total moles become 13+2=15 and the total pressure will be 169/9x15/13=195/9 atm

Krypton molar fraction now is 4/15

hence its partial pressure is molar fractionx total pressure

=(4/15)x(195/9)=52/9 atm=5.7777 atm

Nov 8th, 2014

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