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Half life of a first order reaction is 4 s and the initial concentration of the reactants is 0.12 M. The concentration of the reactant left after 16 s is

1. 0.0075 M
2. 0.06 M
3. 0.03 M
4. 0.015 M

Correct answer: 0.03 M

Solution

For a first-order reaction, the concentration after time t can be calculated using the formula: [A] = [A]₀ × (1/2)^(t/t₁/₂). Here, t = 16 s, t₁/₂ = 4 s, and [A]₀ = 0.12 M. Substituting, [A] = 0.12 × (1/2)^(16/4) = 0.12 × (1/2)^4 = 0.12 × 1/16 = 0.03 M.

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