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For the reaction R -> P, the concentration of R changes from 0.03 M to 0.02 M in 25 minutes. What is the average rate of reaction in M min^-1?
A8.0 x 10^-4
B4.0 x 10^-4
C2.0 x 10^-4
D6.0 x 10^-4
Answer & Solution
Correct answer: B. 4.0 x 10^-4
1. Average rate $= -\dfrac{\Delta[R]}{\Delta t}$.
2. $\Delta[R] = 0.02 - 0.03 = -0.01\ \text{M}$ over $\Delta t = 25\ \text{min}$.
3. $r_{av} = -\dfrac{-0.01}{25} = 4.0\times10^{-4}\ \text{M min}^{-1}$.
4. Distractor A (8.0 x 10^-4) wrongly omits dividing by time span fully or doubles the result.
_Source: NCERT Class 12 Chemistry Ch 3 "Chemical Kinetics", p.5_
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