Half-life period of a first-order reaction is 10 minutes. Starting with 10 mol L−1, rate after 20 minutes will be

To find the rate after 20 minutes, we need to use the concept of half-life in a first-order reaction.

The half-life of a first-order reaction is the time it takes for the concentration of the reactant to decrease by half. In this case, the half-life period is given as 10 minutes.

Since the initial concentration is 10 mol L−1, after one half-life (10 minutes), the concentration will be reduced to 5 mol L−1.

Now, we need to determine how many half-lives have passed in 20 minutes. Since each half-life is 10 minutes, we can divide the total time (20 minutes) by the half-life period (10 minutes) to find the number of half-lives.

20 minutes / 10 minutes = 2 half-lives

Therefore, after 20 minutes, two half-lives have passed.

To find the rate after 20 minutes, we need to determine the concentration after two half-lives.

After the first half-life, the concentration is reduced to 5 mol L−1. After the second half-life, the concentration is reduced by half again:

5 mol L−1 / 2 = 2.5 mol L−1

So, the rate after 20 minutes will be 2.5 mol L−1.