Question

What is the half-life of a first-order reaction with a rate
constant of 4.20×10^{−4} s−1? (the answer is 1650s)

What is the rate constant of a first-order reaction that takes 458 seconds for the reactant concentration to drop to half of its initial value?

Answer #1

The relation between half life (t^{1/2}) and rate
constant k can be given as:

t^{1/2} = 0.693 / k

k = 4.2 X 10^{-4} s^{-1} (given)

So, for first question, t^{1/2} = 0.693 / 4.2 X
10^{-4}

^{
} t^{1/2} = 0.165 X 10^{4} = 1650
s

Similarily,

From above eq. rate constant for 1st order reaction,
**when t = t ^{1/2}**

k =0.693 / t^{1/2}

and t = t^{1/2} = 458 s (given)

So, k =0.693 / 458 = 0.00151 s

k = 1.51 X 10^{-3} s

Half-life equation for first-order reactions:
t1/2=0.693k
where t1/2 is the half-life in seconds (s), and
kis the rate constant in inverse seconds (s−1).
a) What is the half-life of a first-order reaction with a rate
constant of 8.10×10−4 s^−1? Express your answer with the appropriate
units.
b) What is the rate constant of a first-order
reaction that takes 151 seconds for the reactant concentration to
drop to half of its initial value? Express your answer with the appropriate
units.
c) A...

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 (A→products) has a rate constant
of 4.20×10−3 s−1 at 45 ∘C. How many minutes does it take
for the concentration of the reactant, [A],...

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 (A→products ) has a rate constant
of 5.10×10−3 s−1 at 45 ∘C . How many minutes does it
take for the concentration of the...

Part A
A certain first-order reaction (A→products) has a rate constant
of 7.20×10−3 s−1 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?
Express your answer with the appropriate units.
Answer:
6.42 min
Part B
A certain second-order reaction (B→products) has a rate constant
of 1.35×10−3M−1⋅s−1 at 27 ∘Cand an initial
half-life of 236 s . What is the concentration of the reactant B
after...

Part A : A certain first-order reaction (A→products) has a rate
constant of 9.30×10−3 s−1 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?
Part B : A certain second-order reaction (B→products) has a rate
constant of 1.10×10−3M−1⋅s−1 at 27 ∘C and an
initial half-life of 278 s . What is the concentration of the
reactant B after one half-life?

PLEASE MAKE SURE YOUR ANSWERS ARE CORRECT
Part A
What is the half-life of a first-order reaction with a rate
constant of 7.60×10−4 s−1?
Express your answer with the appropriate units.
Part B
A certain first-order reaction has a rate constant of
1.50×10−3 s−1. How long will it take for the reactant
concentration to drop to 18 of its initial value?
Express your answer with the appropriate units.

A) The rate constant for a certain reaction is k = 2.60×10−3 s−1
. If the initial reactant concentration was 0.200 M, what will the
concentration be after 16.0 minutes
B)A zero-order reaction has a constant rate of
4.20×10−4M/s. If after 60.0 seconds the
concentration has dropped to 9.00×10−2M, what
was the initial concentration

The integrated rate law allows chemists to predict the reactant
concentration after a certain amount of time, or the time it would
take for a certain concentration to be reached. The integrated rate
law for a first-order reaction is: [A]=[A]0e−kt Now say we are
particularly interested in the time it would take for the
concentration to become one-half of its initial value. Then we
could substitute [A]02 for [A] and rearrange the equation to:
t1/2=0.693k This equation calculates the time...

The integrated rate law allows chemists to predict the reactant
concentration after a certain amount of time, or the time it would
take for a certain concentration to be reached. The integrated rate
law for a first-order reaction is: [A]=[A]0e−kt Now say we are
particularly interested in the time it would take for the
concentration to become one-half of its inital value. Then we could
substitute [A]02 for [A] and rearrange the equation to: t1/2=0.693k
This equation caculates the time...

The decomposition of hydrogen peroxide (H2O2) is a first order
reaction with a rate constant 1.8×10-5 s -1 at 20°C.
(a) What is the half life (in hours) for the reaction at
20°C?
(b) What is the molarity of H2O2 after four half lives if the
initial concentration is 0.30 M?
(c) How many hours will it take for the concentration to drop to
25% of its initial value?
*Help please!!!*

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