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NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

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Question : 10
Total: 39
In a reaction between A and B, the initial rate of reaction (r0) was measured for different initial concentrations of A and B as given below :
 A/mol L‌–1  B/mol L‌–1   r0/mol L‌−1 s ‌−1
 0.20  0.30   5.07 × 10‌−5
 0.20  0.10  5.07 × 10‌−5
 0.40  0.05  1.43 × 10‌−4
What is the order of the reaction with respect to A and B ?
Solution:  
dx
dt
=k[A]x[B]y
5.07×10−5=k(0.2)x(0.3)y‌‌‌‌‌‌‌‌‌...(i)
5.07×10−5=k(0.2)x(0.10)y‌‌‌‌‌‌‌...(ii)
Dividing (i) by (ii), we get
‌‌1=3y⇒30=3y⇒y=0
5.07×10−5=k(0.2)x(0.1)0‌‌‌‌‌‌‌‌‌...(iii)
1.43×10−4=k(0.4)x(0.05)0‌‌‌‌‌‌‌...(iv)
Dividing (iv) by (iii), we get 2.8 = 2‌x
‌‌‌‌‌‌log‌2.8=x‌log‌2
or ‌‌x=
log‌2.8
log‌2.0

‌‌‌‌‌‌=
0.4472
0.3010
=1.48≈1.5
The order of reaction is 1.5 with respect to ‘A’ and zero with respect to ‘B’.
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