A first order reaction is found to have a rate constant, k = 5 . 5 × 10 - 14 s - 1 . Find the half life of the reaction.

Given : k = 5 . 5 × 10 - 14 s - 1 Solution : Half life period is the time in which the molar concentration of reactants is reduced to half. Half life period of first order reactions : t 1 2 = 0 . 693 k So, t 1 2 = 0 . 693 5 . 5 × 10 - 14 = 1 . 26 × 10 13 s Hence, the value of half life of the reaction comes out to be 1 . 26 × 10 13 s .

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The rate constant for a second order reaction is $k = \frac{2.303}{t (a - b)} \log \frac{b (a - x)}{a (b - x)}$ where $a$ and $b$ are initial concentrations of the two reactants $A$ and $B$ involved. If one of the reactants is present in excess, it becomes pseudo unimolecular. Explain how?

Important Questions on Chemical Kinetics

HARD

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The decomposition reaction $2 N_{2} O_{5} (g) \overset{∆}{\to} 2 N_{2} O_{4} (g) + O_{2} (g)$ is started in a closed cylinder under the isothermal isochoric condition at an initial pressure of $1 atm$ . After $\frac{Y}{10} \times 10^{3} s$ , the pressure inside the cylinder is found to be $1.45 a t m$ . If the rate constant of the reaction is $5 \times 10^{- 4} s^{- 1}$ , assuming ideal gas behaviour, the value of $Y$ is(nearest integer)

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The rate constant for the first order reaction is

60 s^{- 1} .

How much time will it take to reduce the concentration of the reactant to

\frac{1}{16} t h

value?

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

If the rate constant for a first order reaction is

k

, the time

(t)

required for the completion of

99 %

of the reaction is given by

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The rate constant of a first order reaction is

231 \times 10^{- 5} s^{- 1}

. How long will

4 g

of this reactant reduce to

2 g

EASY

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The rate constant for a first order reaction is

7 .0 \times 10^{- 4} s^{- 1} .

If initial concentration of the reactant is

0.080 M

, what is the half-life of the reaction?

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The plot of

t_{1 / 2}

v/s

[R]_{0}

for a reaction is a straight-line parallel to

x

-axis. The unit for the rate constant of this reaction is

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

During the nuclear explosion, one of the products is

^{90} S r

with half life of

6.93

years. If

1 μ g

^{90} S r

was absorbed in the bones of a newly born baby in place of

C a,

how much time, in years, is required to reduce it by

90 %

if it is not lost metabolically ____________.

HARD

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

Which of the following plots is(are) correct for the given reaction?

( $[P]_{0}$ is the initial concentration of $P$ )

Question Image

EASY

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

Which among the following reactions can be an example of pseudo first order reaction?

EASY

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

A first-order reaction has a specific reaction rate

10^{- 2} \sec^{- 1} .

How much time will it take for

20 g

the reactant to reduce to

5 g

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

75 %

of a first order reaction was completed in

90

minutes,

60 %

of the same reaction would be completed in approximately (in minutes) _____
(Take:

\log 2 = 0.30; \log 2.5 = 0.40

)

HARD

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

For a first order reaction

A (g) \to 2 B (g) + C (g)

at constant volume and 300 K, the total pressure at the beginning

(t = 0)

and at time are

p_{0} and p_{t}

, respectively. Initially, only A is present with concentration

{[A]}_{0}

, and

t_{\frac{1}{3}}

is the time required for the partial pressure of A to reach

1 / 3^{rd}

of its initial value. The correct option(s) is (are)
(Assume that all these gases behave as ideal gases)

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

A flask contains a mixture of compounds

A

and

B

. Both compounds decompose by first-order kinetics. The half-lives for

A

and

B

are

300 s

and

180 s

, respectively. If the concentrations of

A

and

B

are equal initially, the time required for the concentration of A to be four times that of

B

(in s) is :

(Use \ln 2 = 0.693)

HARD

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The reaction

2 N_{2} O_{5} (g) \to 4 N O_{2} (g) + O_{2} (g)

follows first order kinetics. The pressure of a vessel containing only

N_{2} O_{5}

was found to increase from 50 mm Hg to 87.5 mm Hg in 30 min. The pressure exerted by the gases after 60 min. Will be (Assume temperature remains constant) :

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The rate constant for a first order reaction is

4.606 \times 10^{- 3} s^{- 1}

. The time required to reduce

2.0 g

of the reactant to

0.2 g

is :

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

Under what condition a bimolecular reaction behaves kinetically first order reaction?

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

A first order reaction is found to have a rate constant,

k = 5.5 \times 10^{- 14} s^{- 1}

. Find the half life of the reaction.

HARD

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The half-life period of a first-order reaction is

15 minutes

. The amount of substance left after one hour will be

EASY

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

When initial concentration of a reactant is doubled in a reaction, its half-life period is not affected. The order of the reaction is:

MEDIUM

Chemistry>Physical Chemistry>Chemical Kinetics>Pseudo First Order Reactions

The rate of a first-order reaction is

0.04 m o l l^{- 1} s^{- 1}

10

second and

0.03 m o l l^{- 1} s^{- 1}

20

seconds after initiation of the reaction. The half-life period of the reaction is:

The rate constant for a second order reaction is k=2.303ta-blogba-xab-x where a and b are initial concentrations of the two reactants A and B involved. If one of the reactants is present in excess, it becomes pseudo unimolecular. Explain how?

Important Questions on Chemical Kinetics

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The rate constant for a second order reaction is $k = \frac{2.303}{t (a - b)} \log \frac{b (a - x)}{a (b - x)}$ where $a$ and $b$ are initial concentrations of the two reactants $A$ and $B$ involved. If one of the reactants is present in excess, it becomes pseudo unimolecular. Explain how?