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± Half-life for First and Second Order Reactions The half-life of a reaction, t1/2, is the time it takes for the reactant concentration [A] to decrease by half. For example, after one half-life the concentration falls from the initial concentration [A]0 to [A]0/2, after a second half-life to [A]0/4, after a third half-life to [A]0/8, and so on. on. For a first-order reaction, the half-life is constant. It depends only on the rate constant k and not on the reactant concentration. It is expressed as t1/2=0.693k For a second-order reaction, the half-life depends on the rate constant and the concentration of the reactant and so is expressed as t1/2=1k[A]0
Part A) A certain first-order reaction (Aâproducts) has a rate constant of 5.40Ã10â3 sâ1 at 45 âC. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration? Express your answer with the appropriate units.
Part B) A certain second-order reaction (Bâproducts) has a rate constant of 1.15Ã10â3 Mâ1â sâ1 at 27 âC and an initial half-life of 282 s . What is the concentration of the reactant B after one half-life? Express your answer with the appropriate units.
For a first-order reaction, the half-life is constant. It depends only on the rate constant k and not on the reactant concentration. It is expressed as t1/2=0.693k For a second-order reaction, the half-life depends on the rate constant and the concentration of the reactant and so is expressed as t1/2=1k[A]0
Part A
A certain first-order reaction (Aâproducts) has a rate constant of 7.50Ã10â3 sâ1 at 45 âC. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration?
Part B
A certain second-order reaction (Bâproducts) has a rate constant of 1.10Ã10â3 Mâ1â sâ1 at 27 âC and an initial half-life of 204 s . What is the concentration of the reactant B after one half-life?