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The rate of a first-order reaction is 0.04 mol ℓ-1 s-1 at 10 seconds and 0.03 mol ℓ-1 s-1 at 20 seconds after initiation of the reaction. The half-life period of the reaction is :
  • a)
    54.1 s
  • b)
    24.1 s
  • c)
    34.1 s
  • d)
    44.1 s
Correct answer is option 'B'. Can you explain this answer?
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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.
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The rate of a first-order reaction is 0.04 molℓ-1 s-1 at 10 seconds and 0.03 mol ℓ-1 s-1 at 20 secondsafter initiation of the reaction. The half-life period of the reaction is :a)54.1 sb)24.1 sc)34.1 sd)44.1 sCorrect answer is option 'B'. Can you explain this answer?
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