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If it takes 30 seconds for a reactant concentration to decrease from 1.0 M to 0.5 M in a first-order chemical reaction, then what is the rate constant for the reaction? A. 0.033 s^–1 B. 0.046 s^–1 C. 0.023 s^–1 D. 43 s^–1

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The answer is A. For a first-order chemical reaction, the rate constant k has a relationship with concentration C as follow: dC/dT=k*C. So in this reaction, (1-0.5)/30=k*0.5. So k=0.033

Answer: 0.023 s^-1

Explanation:

Using the equation: ln(No/N) =kt, we can get k=[ln(No/N)] /t

Thus, k=ln(1/0.5)/30=(ln2)/(30 s) = 0.023 s^-1

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