Chemical Kinetics Questions — JEE Chemistry

Q1

\beta

- particle is emitted in radioactivity by

A conversion of proton to neutron

B from outermost orbit

C conversion of neutron to proton

D

\beta

-particle is not emitted

Correct Answer

Option C

Solution

{}_0{n^1} \to {}_{ + 1}{p^1} + {}_{ - 1}{e^{}}

Q2

The rate of a chemical reaction doubles for every 10oC rise of temperature. If the temperature is raised by 50oC , the rate of the reaction increases by about :

A 24 times

B 32 times

C 64 times

D 10 times

Correct Answer

Option B

Solution

Since for every

{10^ \circ }C

rise in temperature rate doubles for

{50^ \circ }C

rise in temp increase in reaction rate

= {2^5} = 32

times

Q3

In the transformation of

{}_{92}^{238}U

to

{}_{92}^{234}U

, if one emission is an α-particle, what should be the other emission(s)?

A Two

\beta^-

B Two

\beta^-

and one

\beta^+

C One

\beta^-

and one

\gamma

D One

\beta^+

and One

\beta^-

Correct Answer

Option A

Solution

{}_{92}^{238}U\overset{{ - \alpha }}\longrightarrow {}_{90}^{234}Th\overset{{\, - 2\beta }}\longrightarrow {}_{92}^{234}U

Q4

The half-life of a radioactive isotope is three hours. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 hours would be

A 8.0 g

B 12.0 g

C 16.0 g

D 4.0 g

Correct Answer

Option D

Solution

{t_{1/2}} = 3\,

hrs.

T=18

hours as

\,\,\,\,T = n \times {t_{1/2}}

$\therefore$

\,\,\,\,n = {{18} \over 3} = 6

Initial mass

\left( {{C_0}} \right) = 256\,g

$\therefore$

\,\,\,\,{C_n} = {{{C_0}} \over {{2^n}}} = {{256} \over {{{\left( 2 \right)}^6}}} = {{256} \over {64}} = 4g.

Q5

In respect of the equation k = Ae-Ea/RT in chemical kinetics, which one of the following statements is correct?

A A is adsorption factor

B Ea is energy of activation

C R is Rydberg’s constant

D k is equilibrium constant

Correct Answer

Option B

Solution

The Arrhenius equation reads

k = A\,e^{-\tfrac{E_a}{RT}}

Let’s check each term: A is the pre-exponential (or frequency) factor, not an adsorption factor. $E_a$ is indeed the activation energy.

R is the universal gas constant ( $\approx8.314$ \,J·mol⁻¹·K⁻¹), not Rydberg’s constant. k is the rate constant, not the equilibrium constant.

Hence, the correct statement is: Option B: $E_a$ is energy of activation.

Q6

For the reaction A + 2B

\to

C, rate is given by R = [A] [B]2 then the order of the reaction is

A 3

B 6

C 5

D 7

Correct Answer

Option A

Solution

NOTE : Order is the sum of the power of the concentrations terms in rate law expression. Hence the order of reaction is

=1+2=3

Q7

Units of rate constant of first and zero order reactions in terms of molarity M unit are respectively

A sec-1, Msec-1

B sec-1, M

C Msec-1, sec-1

D M, sec-1

Correct Answer

Option A

Solution

For a zero order reaction. rate

= k{\left[ A \right]^ \circ }\,\,\,

i.e. rate

=k

hence unit of

k = M.{\sec ^{ - 1}}

For a first order reaction. rate

= k\left[ A \right]

k=M.

{\sec ^{ - 1}}/M = {\sec ^{ - 1}}

Q8

For the reaction system: 2NO(g) + O2(g)

\to

2NO2(g) volume is suddenly reduce to half its value by increasing the pressure on it. If the reaction is of first order with respect to O2 and second order with respect to NO, the rate of reaction will

A diminish to one-eighth of its initial value

B increase to eight times of its initial value

C increase to four times of its initial value

D diminish to one-fourth of its initial value

Correct Answer

Option B

Solution

r = k\left[ {{O_2}} \right]{\left[ {NO} \right]^2}.

When the volume is reduced to

1/2,

the conc. will double $\therefore$

\,\,\,\,\,

New rate

= k\left[ {2{O_2}} \right]{\left[ {2NO} \right]^2} = 8k\left[ {{O^2}} \right]{\left[ {NO} \right]^2}

The new rate increases to eight times of its initial.

Q9

The radionucleide

{}_{90}^{234}Th

undergoes two successive

\beta

-decays followed by one

\alpha

-decay. The atomic number and the mass number respectively of the resulting radionucleide are

A 94 and 230

B 90 and 230

C 92 and 230

D 92 and 234

Correct Answer

Option B

Solution

{}_{90}^{234}Th\overset{{ - \beta }}\longrightarrow {}_{91}^{234}X\overset{{\, - \beta }}\longrightarrow {}_{92}^{234}Th\overset{{ - \alpha }}\longrightarrow {}_{90}^{230}Th

Q10

The rate equation for the reaction 2A + B

\to

C is found to be: rate k[A][B]. The correct statement in relation to this reaction is that the

A unit of K must be s-1

B values of k is independent of the initial concentration of A and B

C rate of formation of C is twice the rate of disappearance of A

D t1/2 is a constant

Correct Answer

Option B

Solution

The velocity constant depends on temperature only. It is independent of concentration of reactants.