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For the first order reaction N2O5 -> 2NO2 + 1/2 O2 at 318 K, [N2O5] falls from 1.24 x 10^-2 to 0.20 x 10^-2 mol L^-1 in 60 minutes. What is the rate constant? (log 6.2 = 0.792)
A0.0304 min^-1
B0.0792 min^-1
C0.0152 min^-1
D0.0608 min^-1
Answer & Solution
Correct answer: A. 0.0304 min^-1
1. $k = \dfrac{2.303}{t}\log\dfrac{[R]_0}{[R]}$.
2. $\dfrac{[R]_0}{[R]} = \dfrac{1.24\times10^{-2}}{0.20\times10^{-2}} = 6.2$.
3. $k = \dfrac{2.303}{60}\times\log 6.2 = \dfrac{2.303}{60}\times0.792$.
4. $= 0.03838\times0.792 = 0.0304\ \text{min}^{-1}$.
5. Distractor B forgets to divide by t (60); distractor C halves the correct answer.
_Source: NCERT Class 12 Chemistry Ch 3 "Chemical Kinetics", p.13_
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