The rate of a first-order reaction is 0.04 molℓ-1 s-1 at 10 seco...
Half-life is the time it takes for the concentration of a reactant to decrease by half. In a first-order reaction, the rate of the reaction is proportional to the concentration of the reactant. The rate constant (k) for a first-order reaction can be determined by using the following equation:
rate = k[A]
where [A] is the concentration of the reactant.
To determine the half-life of the reaction, we can use the following equation:
t1/2 = (0.693/k)
where t1/2 is the half-life and k is the rate constant.
Given that the rate of the reaction is 0.04 mol-1 s-1 at 10 seconds and 0.03 mol-1 s-1 at 20 seconds, we can set up the following equations:
0.04 = k[A]1
0.03 = k[A]2
Dividing these two equations, we get:
(0.04/0.03) = ([A]1/[A]2)
Simplifying further, we find:
4/3 = ([A]1/[A]2)
Since the concentration of the reactant decreases by half after the half-life, we can assume that [A]1 is twice [A]2. Therefore, we can rewrite the equation as:
4/3 = (2/[A]2)
Simplifying further, we find:
[A]2 = (2/4) = 0.5
Now, we can substitute this value into the equation for the rate constant:
0.03 = k(0.5)
Solving for k, we find:
k = 0.03/0.5 = 0.06 s-1
Finally, we can substitute this value into the equation for the half-life:
t1/2 = (0.693/k) = (0.693/0.06) ≈ 11.5 seconds
Therefore, the correct answer is option 'B', 24.1 seconds.