# Transcribed Image Text: I Review | Constants | Periodic Table

Transcribed Image Text: I Review | Constants | Periodic Table
The half-life of a reaction, t12, 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]o to [A]o/2, after a second half-life to [A]o/4:
after a third half-life to Alo /8, and so on. on.
Value
min
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Part B
A certain second-order reaction (B→products) has a rate constant of 1.80×103 M-s-1 at 27°C and an
initial half-life of 246 s. What is the concentration of the reactant B after one half-life?
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HA
Value
M

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]o to [A]o/2, after a second half-life to [A]o/4;
after a third half-life to [Ao/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
0.693
t1/2
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 =
Part A
A certain first-order reaction (A→products) has a rate constant of 3.60x103s at 45 °C. How many
minutes does it take for the concentration of the reactant, A, to drop to 6.25% of the original concentration?