Chemical Kinetics: JEE Main Previous Year Questions (2021-2026)

 Page 1


JEE Main Previous Year Questions (2021-2026): 
Chemical Kinetics   
 
(January 2026) 
Q1: An organic compound undergoes first order decomposition. The time taken 
for decomposition to (1/8)
th
 and (1/10)
th
 of its initial concentration are t
1/8 
 and t
1/10
  
respectively. 
What is the value of ? 
(log  2 = 0.3) 
A: 30 
B: 9 
C: 3 
D: 0.9 
Answer: B 
Explanation: 
For a first order reaction, the integrated rate law is 
 
Page 2


JEE Main Previous Year Questions (2021-2026): 
Chemical Kinetics   
 
(January 2026) 
Q1: An organic compound undergoes first order decomposition. The time taken 
for decomposition to (1/8)
th
 and (1/10)
th
 of its initial concentration are t
1/8 
 and t
1/10
  
respectively. 
What is the value of ? 
(log  2 = 0.3) 
A: 30 
B: 9 
C: 3 
D: 0.9 
Answer: B 
Explanation: 
For a first order reaction, the integrated rate law is 
 
 
 
 
 
Q2: A ? D is an endothermic reaction occurring in three steps (elementary). 
(i) A ? B?H
i
 = +ve 
(ii) B ? C?H
ii
 = -ve 
(iii) C ? D?H
iii
 = -ve 
Which of the following graphs between potential energy (y-axis) vs reaction 
coordinate (x-axis) correctly represents the reaction profile of A ? D? 
Page 3


JEE Main Previous Year Questions (2021-2026): 
Chemical Kinetics   
 
(January 2026) 
Q1: An organic compound undergoes first order decomposition. The time taken 
for decomposition to (1/8)
th
 and (1/10)
th
 of its initial concentration are t
1/8 
 and t
1/10
  
respectively. 
What is the value of ? 
(log  2 = 0.3) 
A: 30 
B: 9 
C: 3 
D: 0.9 
Answer: B 
Explanation: 
For a first order reaction, the integrated rate law is 
 
 
 
 
 
Q2: A ? D is an endothermic reaction occurring in three steps (elementary). 
(i) A ? B?H
i
 = +ve 
(ii) B ? C?H
ii
 = -ve 
(iii) C ? D?H
iii
 = -ve 
Which of the following graphs between potential energy (y-axis) vs reaction 
coordinate (x-axis) correctly represents the reaction profile of A ? D? 
A:  
B:  
C:  
D:  
Answer: D 
Explanation: 
Given: 
A ? D; ?
r
H = (+)ve = E
D
 - E
A
 ? E
D
 > E
A
 
Mechanism 
A ? B; ?
r
H = (+)ve ? E
B
 > E
A
 
Page 4


JEE Main Previous Year Questions (2021-2026): 
Chemical Kinetics   
 
(January 2026) 
Q1: An organic compound undergoes first order decomposition. The time taken 
for decomposition to (1/8)
th
 and (1/10)
th
 of its initial concentration are t
1/8 
 and t
1/10
  
respectively. 
What is the value of ? 
(log  2 = 0.3) 
A: 30 
B: 9 
C: 3 
D: 0.9 
Answer: B 
Explanation: 
For a first order reaction, the integrated rate law is 
 
 
 
 
 
Q2: A ? D is an endothermic reaction occurring in three steps (elementary). 
(i) A ? B?H
i
 = +ve 
(ii) B ? C?H
ii
 = -ve 
(iii) C ? D?H
iii
 = -ve 
Which of the following graphs between potential energy (y-axis) vs reaction 
coordinate (x-axis) correctly represents the reaction profile of A ? D? 
A:  
B:  
C:  
D:  
Answer: D 
Explanation: 
Given: 
A ? D; ?
r
H = (+)ve = E
D
 - E
A
 ? E
D
 > E
A
 
Mechanism 
A ? B; ?
r
H = (+)ve ? E
B
 > E
A
 
B ? C; ?
r
H = (-)ve ? E
C
 < E
B
 
C ? D; ?
r
H = (-)ve ? E
D
 < E
C 
 
 
Q3: At 27°C in presence of a catalyst, activation energy of a reaction is lowered 
by 10 kJ mol ?¹. The logarithm of ratio of  
(Consider that the frequency factor for both the reactions is same) 
A: 1.741 
B: 0.1741 
C: 17.41 
D: 3.482 
Answer: A 
Explanation: 
Arrhenius equation (NCERT): 
 
Given: catalyst lowers activation energy by 10 kJ mol
-1 
= 10000 J mol
-1
 and frequency 
factor A is same. 
So, 
At 27°C, T = 300 K and R = 8.314 J mol ?¹ K ?¹: 
Page 5


JEE Main Previous Year Questions (2021-2026): 
Chemical Kinetics   
 
(January 2026) 
Q1: An organic compound undergoes first order decomposition. The time taken 
for decomposition to (1/8)
th
 and (1/10)
th
 of its initial concentration are t
1/8 
 and t
1/10
  
respectively. 
What is the value of ? 
(log  2 = 0.3) 
A: 30 
B: 9 
C: 3 
D: 0.9 
Answer: B 
Explanation: 
For a first order reaction, the integrated rate law is 
 
 
 
 
 
Q2: A ? D is an endothermic reaction occurring in three steps (elementary). 
(i) A ? B?H
i
 = +ve 
(ii) B ? C?H
ii
 = -ve 
(iii) C ? D?H
iii
 = -ve 
Which of the following graphs between potential energy (y-axis) vs reaction 
coordinate (x-axis) correctly represents the reaction profile of A ? D? 
A:  
B:  
C:  
D:  
Answer: D 
Explanation: 
Given: 
A ? D; ?
r
H = (+)ve = E
D
 - E
A
 ? E
D
 > E
A
 
Mechanism 
A ? B; ?
r
H = (+)ve ? E
B
 > E
A
 
B ? C; ?
r
H = (-)ve ? E
C
 < E
B
 
C ? D; ?
r
H = (-)ve ? E
D
 < E
C 
 
 
Q3: At 27°C in presence of a catalyst, activation energy of a reaction is lowered 
by 10 kJ mol ?¹. The logarithm of ratio of  
(Consider that the frequency factor for both the reactions is same) 
A: 1.741 
B: 0.1741 
C: 17.41 
D: 3.482 
Answer: A 
Explanation: 
Arrhenius equation (NCERT): 
 
Given: catalyst lowers activation energy by 10 kJ mol
-1 
= 10000 J mol
-1
 and frequency 
factor A is same. 
So, 
At 27°C, T = 300 K and R = 8.314 J mol ?¹ K ?¹: 
 
So, 
 
 
Q4: 
 
Given above is the concentration vs time plot for a dissociation reaction : A ? 
nB. 
Based on the data of the initial phase of the reaction (initial 10 min ), the value of 
n is ________. 
A: 2 
B: 5 
C: 4 
D: 3 
Answer: D 
Explanation: 
From the graph, in the first 10 minutes the concentration of A decreases from 0.05 to 
0.04. 
So, the amount of A dissociated in 10 minutes = 0.05 - 0.04 = 0.01. 
For the reaction A ? nB, when 0.01 of A reacts, B formed = 0.01 × n. 
From the graph, in the same time interval, concentration of B formed becomes 0.03. So 
we equate 0.01 × n to 0.03 and find n. 
A ? nB 
0.05  0