Question

If 16g if a radioactive substance are present initially and 5yr later only 8g remain how much substance will be present after 5yr

Answer 1

4.59 g will be the amount of substance that will be present after 5 year.

Given: 16g of radioactive substance

            8g left after 8 year

Concept: In a chemical reaction, the half-life of a species is the time it takes for the concentration of that substance to drop to half its original value. In a first-order reaction, the half-life of the reactant is ln(2)/λ, where λ (also referred to as k) is the reaction rate constant.

The half-life is given as 5 years, so the amount remaining after 9 years will be found by using the steps done below:

Remaining amount of radioactive substance = initial × (1/2)^(t/(half-life))

Remaining substance = (16 g)×(1/2)^(9/5) ≈ 4.59 g

After 9 years i.e., after 8 years have passed

About 4.59 g of the substance remains.

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