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Karnataka Board PUCPUC Science 2nd PUC Class 12

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: What is the order of the reaction with respect to A and B?

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Question

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 0.20 0.20 0.40
B/mol L−1 0.30 0.10 0.05
r0/mol L−1 s−1 5.07 × 10−5 5.07 × 10−5 1.43 × 10−4

What is the order of the reaction with respect to A and B?

Numerical
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Solution

Suppose the order of the reaction with respect to A is m and with respect to B is n.

∴ Rate (r0) = k[A]m [B]n

For the given data, we have,

Rate (r1) = 5.07 × 10−5

= k (0.20)m × (0.30)n    ...(i)

Rate (r2) = 5.07 × 10−5

= k (0.20)m × (0.10)n    ...(ii)

Rate (r3) = 1.43 × 10−4

= k (0.40)m × (0.05)n    ...(iii)

Dividing eq. (i) by eq. (ii), we have,

`(5.07 xx 10^-5)/(5.07 xx 10^-5) = (k (0.20)^m xx (0.30)^n)/(k (0.20)^m xx (0.10)^n)`

⇒ 1 = (3)n

⇒ n = 0

Dividing eq. (iii) by eq. (ii) and putting the value of n, we get,

`(1.43 xx 10^-4)/(5.07 xx 10^-5) = (k (0.40)^m xx (0.05)^0)/(k (0.20)^m xx (0.10)^0)`

⇒ `(1.43 xx 10^-4)/(5.07 xx 10^-5)` = 2m

⇒ (2)m = 2.82

⇒ m log10 2 = log10 2.82 = 0.45

⇒ m = `0.45/(log_10 2)`

= `0.45/0.3010`

= 1.49

= 1.50

Hence, the order with respect to A is 1.5, and the order with respect to B is 0.

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Chapter 3: Chemical Kinetics - Exercises [Page 86]

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NCERT Chemistry Part 1 and 2 [English] Class 12
Chapter 3 Chemical Kinetics
Exercises | Q 3.10 | Page 86
Nootan Chemistry [English] Class 12 ISC
Chapter 3 Chemical Kinetics
'NCERT TEXT-BOOK' Exercises | Q 4.10 | Page 279

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