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

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JEE Main Previous Year Questions (2021-2026): 
Chemical Equilibrium 
 
(January 2026) 
 
Q1: Observe the following equilibrium in a 1 L flask. 
A(g) ? B(g) 
At T(K), the equilibrium concentrations of A and B are 0.5 M and 0.375 M respectively. 0.1 
moles of A is added into the flask and heated to T(K) to establish the equilibrium again. 
The new equilibrium concentrations (in M) of A and B are respectively: 
A: 0.742, 0.557 
B: 0.367, 0.275 
C: 0.53, 0.4 
D: 0.557, 0.418 
Answer: D 
Explanation: 
 
Now 0.1 mole of A is added so reaction will move in forward direction. 
A ? B 
0.6 - x 0.375 + x 
 
Moles of A = 0.043 = 0.557 
Moles of B = 0.418 
 
Q2: Consider the following gaseous equilibrium in a closed container of volume ‘V’ at 
T(K). 
P 2(g) + Q 2(g) ? 2PQ(g) 
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JEE Main Previous Year Questions (2021-2026): 
Chemical Equilibrium 
 
(January 2026) 
 
Q1: Observe the following equilibrium in a 1 L flask. 
A(g) ? B(g) 
At T(K), the equilibrium concentrations of A and B are 0.5 M and 0.375 M respectively. 0.1 
moles of A is added into the flask and heated to T(K) to establish the equilibrium again. 
The new equilibrium concentrations (in M) of A and B are respectively: 
A: 0.742, 0.557 
B: 0.367, 0.275 
C: 0.53, 0.4 
D: 0.557, 0.418 
Answer: D 
Explanation: 
 
Now 0.1 mole of A is added so reaction will move in forward direction. 
A ? B 
0.6 - x 0.375 + x 
 
Moles of A = 0.043 = 0.557 
Moles of B = 0.418 
 
Q2: Consider the following gaseous equilibrium in a closed container of volume ‘V’ at 
T(K). 
P 2(g) + Q 2(g) ? 2PQ(g) 
2 moles each of P 2(g), Q 2(g) and PQ(g) are present at equilibrium. Now one mole each of 
P 2 and Q 2 are added to the equilibrium keeping the temperature at T(K). 
The number of moles of P 2, Q 2 and PQ at the new equilibrium, respectively, are: 
A: 2.56, 1.62, 2.24 
B: 2.67, 2.67, 2.67 
C: 1.21, 2.24, 1.56 
D: 1.66, 1.66, 1.66 
Answer: B 
Explanation: 
For the equilibrium 
 
1) Find K
c
  from the given equilibrium 
Initially at equilibrium: 
 n
P2
 = 2, ?n
Q2
 = 2, ?n
PQ
 = 2 
 
2) After adding 1 mol each of P
2
  and Q
2  
Immediately after addition: 
 n
P2
 = 3, ?n
Q2
 = 3, ?n
PQ
 = 2 
Let the reaction proceed forward by extent xxx: 
n
P2
 = 3 - x,n
Q2
 = 3 - x,n
PQ
 = 2 + 2x 
Apply K
c 
= 1