﻿ NEET Important Questions of Chemical Kinetics | Zigya

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# Chemical Kinetics

#### Multiple Choice Questions

1.

The rate of a reaction doubles when its temperature changes from 300K to 310K. Activation energy of such a reaction will be (R = 8.314 JK–1 mol–1 and log 2 = 0.301)

• 53.6 kJ mol-1

• 48.6 kJ mol-1

• 58.5 kJ mol-1

• 60.5 kJ mol-1

A.

53.6 kJ mol-1

By using Arrhenius equation,

Given, T2 = 310; T1 = 300K
On putting values in Eq (i), we get

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2.

Decomposition of H2O2 follows a first order reaction. In fifty minutes the concentration of H2O2 decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of H2O2 reaches 0.05 M, the rate of formation of O2 will be:

• 6.93×10−4 mol min−1

• 2.66 L min−1 at STP

• 1.34×10−2 mol min−1

• 6.93×10−2 mol min−1

A.

6.93×10−4 mol min−1

For first order reaction

Alternative Method:
If fifty minutes, the concentration of H2O2 decreases from 0.5 to 0.125 M or in one half-life, concentration of H2O2 decreases from 0.5 to 0.25 M. In two half-lives, concentration of H2O2 decreases from 0.5 to 0.125 M or 2t1/2 = 50 min
t1/2 = 25 min
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3.

The resistance of 0.2 M solution of an electrolyte is 50 Ω. The specific conductance of the solution of 0.5 M solution of the same electrolyte is 1.4 S m-1 and resistance of the same solution of the same electrolyte is 280 Ω. The molar conductivity of 0.5 M solution of the electrolyte in Sm-2 mol-1 is

• 5 x 10-4

• 5 x 10-3

• 5 x 103

• 5 x 102

A.

5 x 10-4

For first solution,
k = 1.4 Sm-1, R =50 Ω , M =0.2
specific conductance

588 Views

4.

Two reactions R1 and R2 have identical pre-exponential factors. Activation energy of R1 exceeds that of R2 by 10 kJ mol–1. If k1 and k2 are rate constants for reactions R1 and R2 respectively at 300 K, then ln(k2/k1) is equal to-
(R = 8.314 J mol–1K–1)

• 8

• 12

• 6

• 4

D.

4

From Arrhenius equation

1338 Views

5.

Rate law for the reaction, A+ B → product is rate = k[A]2[B] What is the rate constant; if rate of reaction at a given temperature is 0.22 Ms-1, when [A]= 1 M band [BJ= 0.25 M?

• 3.52 M-2s-1

• 0.88  M-2s-1

• 1.136  M-2s-1

• 0.05  M-2s-1

B.

0.88  M-2s-1

6.

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

• 10 times

• 24 times

• 32 times

• 64 times

C.

32 times

For every 10o C rise of temperature, the rate is doubled. Thus, temperature coefficient of the reaction = 2 when temperature is increased by 50o rate becomes

200 Views

7.

For the non- stoichiometric reaction 2A + B → C + D, the following kinetic data were obtained in three separate experiment, all at 298 K.

 Initial concentration (A) Initial concnetration (B) Initial rate of formation of C (mol L-1 S-1) 1 0.1 M 0.1 M 1.2 x 10-3 2 0.1 M 0.2 M 1.2 x 10-3 3 0.2 M 0.1 M 2.4 x 10-3
The rate law for the formation of C is

D.

where x = order of reaction w.r.t A
y = order of reaction w.r.t B
1.2 x 10-3 = k (0.1)x (0.1)y
1.2 x 10-3 = k (0.1)x (0.2)y
2.4 x 10-3 = k(0.2)x (0.1)y
R = k [A]1[B]0

As shown above, rate of reaction remains constant as the concentration of  reactant (B) changes from 0.1 M to 0.2 M and becomes double when concentration of A change from 0.1 to 0.2
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8.

Higher order (>3) reactions are rare due to:

• the increase in entropy and activation energy as more molecules are involved.

• shifting of equilibrium towards reactants due to elastic collisions

• loss of active species on a collision

• low probability of simultaneous collision of all the reacting species

A.

the increase in entropy and activation energy as more molecules are involved.

Conditions for the occurrence of a reaction:

(i)  Proper orientation and effective collision of the reactants.
(ii)  the chances of simultaneous collision with proper orientation between more than 3 species are very rare, so reaction with order greater than 3 are rare.

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9.

For a first order reaction, (A) → products, the concentration of A changes from 0.1 M to 0.025 M in 40 minutes. The rate of reaction when the concentration of A is 0.01 M is

• 1.73 x 10–5 M/ min

• 3.47 x 10–4 M/min

• 3.47 x 10–5 M/min

• 1.73 x 10–4 M/min

B.

3.47 x 10–4 M/min

By first order kinetic rate constant,

550 Views

10.

The time for half life period of a certain reaction A → Products is 1 hour. When the initial concentration of the reactant ‘A’ is 2.0 mol L–1, how much time does it take for its concentration to come from 0.50 to 0.25 mol L–1 if it is a zero order reaction?

• 1 h

• 4 h

• 0.25 h

• 0.5 h

C.

0.25 h

Given that [A]o = 2 mol L-1

342 Views