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For a first order reaction (A) → products the concentration of A changes from 0.1 M to 0.025 M in 40 minutes. The rate of reaction when the concentration of A is 0.01 M is :

1. 1.73 × 10⁻⁵ M/min
2. 3.47 × 10⁻⁴ M/min
3. 3.47 × 10⁻⁵ M/min
4. 1.73 × 10⁻⁴ M/min

Correct answer: 1.73 × 10⁻⁵ M/min

Solution

The rate of a first-order reaction is directly proportional to the concentration of the reactant. By calculating the rate constant from the change in concentration over time and applying it to the concentration of A at 0.01 M, we find that the rate is 1.73 × 10⁻⁵ M/min.

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