Question 4.20: For the decomposition of azoisopropane to hexane and nitrogen at 543 K, the following data are obtained.
Calculate the rate constant.
Answer
Let initial pressure = po
And pressure after time t = pt
Amount of substance = a
Decomposed quantity = x
The decomposition of azoisopropane to hexane and nitrogen at 543 K is
In this problem we take pressure in place of concentration or quantity
Final pressure due to reactant = po - p = 2po - pt
Plug the values from the table we get
When t = 360 sec
k1 = 2.175 × 10−3 s−1
When t = 720 sec
K2= 2.235 × 10−3 sec−1
Hence, the average value of rate constant is
To get average value add both values and divide by 2 we get
k = (k1 +k2)/2
After calculation we get
k= 2.21 × 10−3 sec−1
Calculate the rate constant.
Answer
Let initial pressure = po
And pressure after time t = pt
Amount of substance = a
Decomposed quantity = x
The decomposition of azoisopropane to hexane and nitrogen at 543 K is
In this problem we take pressure in place of concentration or quantity
Final pressure due to reactant = po - p = 2po - pt
Plug the values from the table we get
When t = 360 sec
k1 = 2.175 × 10−3 s−1
When t = 720 sec
K2= 2.235 × 10−3 sec−1
Hence, the average value of rate constant is
To get average value add both values and divide by 2 we get
k = (k1 +k2)/2
After calculation we get
k= 2.21 × 10−3 sec−1
The blog is nice and informative but i have some problem with this particular question. first, the formula used to calculate k is for first order reaction(which is not specified in question), so how do we know that it is first order reaction. secondly why is the numerical answer different from NCERT textbook answer given at last pages. any help will be appreciated,thanks
ReplyDeleteSudhir Attri! I have the same question! How to know its first order reaction?
ReplyDeleteIf we analyze the data then reaction progress seems to be nearly independent of concentration. Hence..F.o.
ReplyDeletewe know it is a 1st order rxn because decomposition reactions generally tend to be 1st order rxns
ReplyDelete