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CBSE Class 12 Chemistry 2019 Delhi Set 1 Solved Paper

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Question : 13 of 27
Marks: +1, -0
SECTION - C
The decomposition of NH3\mathrm{NH}_3 on platinum surface is zero order reaction. If rate constant k is 4×10−3  Ms−4 \times 10^{-3} \; \mathrm{Ms}^{-} 1{}^1, how long will it take to reduce the initial concentration of NH3\mathrm{NH}_3 from 0.1  M0.1\; \mathrm{M} to 0.064  M0.064\; \mathrm{M}.
Solution:  
The equation for the zero order reaction is:
[A]=[A0]−kt[A] = [A_0] - k t
Given:
[A0]  =0.1  M[A_0] \; = 0.1\; \mathrm{M}
[A]  =0.064[A] \; = 0.064
k  =4×10−3  M/sk \; = 4 \times 10^{-3} \; \mathrm{M} / \mathrm{s}
Putting the values in the equation, and solving the equation for tt, we get:
0.064  =0.1−(4×10−3×t)0.064 \; = 0.1 - (4 \times 10^{-3} \times t)
0.064−0.1  =−(4×10−3×t)0.064 - 0.1 \; = - (4 \times 10^{-3} \times t)
−0.036  =−(4×10−3×t)-0.036 \; = - (4 \times 10^{-3} \times t)
t  =−0.036−4×10−3  =9 st \; = \frac{-0.036}{-4 \times 10^{-3}} \; = 9\ \mathrm{s}
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