Q. For the reaction : 2NO(g) +Cl(g) $\to$2NOCl (g)
The following data were collected. All the measurements were taken at 263 K.

Exp. No.	Initial [NO] [M]	Initial[$C{l}_2$](M)	Initial rate of disapp. Of $C{l}_2$(M/min)
1.	0.15	0.15	0.60
2.	0.15	0.30	1.20
3.	0.30	0.15	2.40
4.	0.25	0.25	?

(i) Write the expreseon for rate law. 
(ii) Calculate the value of rate constant and specify its units. 
(iii) What is the initial rate.of disappearance of $C{l}_2$ in exp. 4? 

 

Dear student,



Let the rate law is given as : Rate  =  K [NO]^a  [Cl₂]^b
(i) Now from the given datas : when we determine the order of reaction with respect to Cl₂ , then we have to choose two such experimental data of NO in which its concentration remains constant and vice- versa for the order of NO .
  Now from the experiment 1 and 2 , concentration of NO remains constant and at the same time Cl₂  make their concentration double and if we see the values of rate it will also make double , indicates that variation of rate is directly proportinal to the variation of concentration of Cl₂ , which means order of reaction with respect to Cl₂ is 1st order and similarly for NO from experiment 1 and 3 variation order of reaction with respect to NO is 2nd order 
    Then the rate law is  :  Rate = K [NO]² [Cl₂]¹
(ii) In the above given law , on putting the values from any experiment ( say from 1 )
             1.20  = K [0.15]² [0.15]  Then K =  4 $\times$ 10² L²mol^-2s^-1
(iii)  From the above given rate law : Rate =  4 $\times$ 10²  [0.25]² [0.25]  = 6.25 mol L^-1s^-1
  Regards