IIT JEE past question Kinetics 4

The vapour pressure of two miscible liquids A and B are 300 and 500 mm Hg respectively.

In a flask10 moles of A is mixed with 12 moles of B.
However as soon as B is added A starts polymerizing into a completely insoluble solid. The polymerization follows first order kinetics. After 100 minutes, 0.525 mole of a solute is dissolved which arrests the polymerization completely. The final vapour pressure of the solution is 400 mm of Hg . Estimate the rate constant of the polymerization reacton.

Assume negligible volume change on mixing and polymerization and ideal behaviour for the final solution.

21 Answers

1
JOHNCENA IS BACK ·

nishant sir,plz check the solution.

1
skygirl ·

yep i did this q myself today ...

and i got 1X10^-4 ... which suddenly clicked that gagar bhaiya too told about this ans...

but how come the ans published everywhere is given 1.2X10^-2 ??

1
JOHNCENA IS BACK ·

ya,but frankly speaking it is not tough although i must have checked the values.

1
JOHNCENA IS BACK ·

yes,i admit my mistake.i had done kinetics far back and star marked a few important as well as worng ques.(which i was not getting ans) when i saw the ques. i thought i had done it as i had star marked it but i had marked it for wrong ans. instead.so,in a hurry i did not check the values and posted the solution.

after solving it i get answer 1.013*10-4 min-1

1
gagar.iitk ·

skygirl the solution from johncena is correct a minor calculation mistake though, i am repeating it .............

let no. of moles of A after 100 min=x
just before addition of solute,A=x and B=12

vapor pressure of solution,p°=x/x+12 *300 + 12/x+12 * 500.........(i)

after adding solute,p=400

p°-p/p°=0.525/0.525+x+12......................................................(ii)

from (i) and (ii) get x=9.9

now for polymerisation reaction(first order)

k=2.303/100 *log(10/9.9)

k=1*10-4

1
skygirl ·

ans is dat only bhaiya[s] ....

i told the ans from RC Mukherjee.

but their they did it how only Mr. Mukherjee knows!!

if anyone has the book and can figure out the solution,,,,'

dooooooooo tell!

62
Lokesh Verma ·

john.. gaurav pointed out an error in it..

Your calculation is flawed.. please check it again....

I am also getting x=9.9 as gaurav pointed out to me in private!

Somehow I also got biased becasue FIITJEE has the same answer and both your equations were correct!

1
skygirl ·

ohhh!! great!

62
Lokesh Verma ·

this was a ten mark question in IIT JEE 2001!

62
Lokesh Verma ·

yes john.. awesome work :)

1
JOHNCENA IS BACK ·

helloooooooooooooooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!is anyone there.

1
skygirl ·

this is a question !!....... i am dying to understand ...!! for many days now....

i even have the solution.. but cudn understand one word of it!

1
JOHNCENA IS BACK ·

is my ans. correct,nishant sir.

1
JOHNCENA IS BACK ·

very easy question.....

let no. of moles of A after 100 min=x
just before addition of solute,A=x and B=12

vapor pressure of solution,p°=x/x+12 *300 + 12/x+12 * 500.........(i)

after adding solute,p=400

p°-p/p°=0.525/0.525+x+12......................................................(ii)

from (i) and (ii) get x=2.84

now for polymerisation reaction(first order)

k=2.303/100 *log(10/2.84)

k=1.2 * 10-2 min-1

1
skygirl ·

no bhaiya ans is 1.2X10-2 min-1 ..

john did u get it ?

1
JOHNCENA IS BACK ·

ans. is 1.2 *10 -2 min-1

1
gagar.iitk ·

K=1*10-4

do tell me if my ans is right then i will post the solution

1
skygirl ·

arey pls dun do it !

a cordial request!

nothing can i understand.......... .. all looks so dirty ..

62
Lokesh Verma ·

hmm.. john you are right.. i had thought about that.. but then it becomes very clumsy handling those questions..

what i will do is put a single thread with all those questions together :)

11
Mani Pal Singh ·

@CENA
HE IS NO DUDE

HE IS A TEACHER AND NOT A STUDENT
SI HE DESERVES RESPECT

AND THE PURPOSE OF MAKING SO MANY THREADS IS TO MAKE IT CLEAN AND CLEAR
AND NOT DO HOTCH POCH

SO BETTER TRY TO ANSWER THE QUESTIONS RATHER THAN COMPLAINING[1]

1
JOHNCENA IS BACK ·

HEY DUDE I THINK THAT IT WUD HAVE BEEN BETTER IF U HAD POSTED ALL KINETICS DOUBT UNDER ONE THREAD INSTEAD OF MAKING SO MANY TOPICS.

IT WUD HAVE SERVED AS A NICE COLLECTION AS WELL AS HELPED TO KEEP THE FORUM NEAT AND CLEAN.

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