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NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

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Question : 2
Total: 39
For the reaction : 2A + B → A‌2B the rate=k[A][B]2 with k =2.0×10–6 mol–2 L2 s–1. Calculate the initial rate of the reaction when [A] = 0.1 mol L‌–1, [B] = 0.2 mol L‌–1. Calculate the rate of reaction after [A] is reduced to 0.06 mol L‌–1.
Solution:  
Initial rate =k[A][B]2 =(2.0×10−6 )×(0.1)×(0.2)2 =8×10−9 mol L−1 s−1
When [A] is reduced from 0.10 molL–1 to 0.06 molL–1 , i.e.0.04 molL–1 of A has reacted. Then according to equation, amount of B reacted is half of A.
[B]=
1
2
×0.04 mol L−1 =0.02mol L−1
Hence, [B] =0.2−0.02=0.18 mol L−1
Now, again rate =k[A][B]2
∴‌ Rate = (2.0×10−6 )×(0.06)×(0.18)2 =3.89×10−9 mol L−1 s−1
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