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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