Question

please show all work i need to know how to do this for a test

The reaction AB is first order in (A). Consider the following data. Time (s) 0.0 5.0 10.0 15.0 20.0 [A] (M) 0.20 0.14 0.10 0.071 0.050 The concentration of A is Mafter 40.0 s. 1.3 e-2 O 0.17 O 3.5 e-4 0 0.025 1.2

Answer 1

For the first order reaction

ln(A0/At) = kt

We can see that the concentration drops from 0.20M to 0.10M in 10 seconds, hence the half-life is 10 seconds. After 40 seconds, it will be 4 half lifes

Concentration after 40 seconds = 0.20/2^4 = 0.0125 (hence the correct answer is 1.3* 10^(-2) or 1.3 e-2)

First option is correct answer.

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