JEE Main Previous Year Questions (2016- 2024): Equilibrium PDF Download

Q.1. The ammonia (NH₃) released on quantitative reaction of 0.6 g urea (NH₂CONH₂) with sodium hydroxide (NaOH) can be neutralized by    (2020)
(1) 200 mL of 0.4 N HCl
(2) 200 mL of 0.2 N HCl
(3) 100 mL of 0.2 N HCl
(4) 100 mL of 0.1 N HCl
Ans. (3)
From the stoichiometry of the reaction,

1 mol of urea liberates 2 moles of ammonia

Thus, moles of ammonia formed = 2×0.01 = 0.02 mol
Since, 1 mol HCl is required to neutralized 1 mol of ammonia. So, 0.02 moles of HCl is required to neutralized 0.02 moles of ammonia.
From the given concentration of HCl, 100 mL of 0.2 N is equivalent to 0.02 moles of ammonia.
⇒ Moles of HCl = 0.1 × 0.2 = 0.02 moles

Q.2. 3 g of acetic acid is added to 250 mL of 0.1 M HCl and the solution made up to 500 mL. To 20 mL of this solution 1/2mL of 5 M NaOH is added. The pH of the solution is ______.
[Given: pK_a of acetic acid = 4.75, molar mass of acetic acid = 60 g mol^–1, log 3 = 0.4771]
Neglect any changes in volume.    (2020)
Ans. (5.23)
Millimoles of AcOH in 20 mL solution = 2
Millimoles of 0.05 M HCl in 20 mL solution = 1
Millimoles of 0.5 mL of 5 M NaOH in 20 mL solution = 2.5
Thus, remaining millimoles of NaOH react with acetic acid in the solution

From the Henderson Hasselbalch equation
 ...(i)
Substituting the value in Eq. (1), we get

⇒ pH = 4.75 + 0.4771   [Given: log 3 = 0.4771]
⇒ pH = 5.23

Q.3. The stoichiometry and solubility product of a salt with the solubility curve given below is, respectively    (2020)

(1) X₂ Y, 2 x 10^-9 M³
(2) XY₂, 4 x 10^-9 M³
(3) XY₂, 1 x 10^-9 M³ 
(4) XY₂, 2 x 10^-6 M³
Ans. (2)
From the graph

Stoichiometry of the compound is XY₂
Solubility product
= 4 x 10^-9 M³

Q.4. Assertion: The pH of water increases with increase in temperature.
Reason: The dissociation of water into H⁺ and OH⁻ is an exothermic reaction.    (2020)
(1) Both assertion and reason are true, and the reason is the correct explanation for the assertion.
(2) Both assertion and reason are false.
(3) Both assertion and reason are true, but the reason is not the correct explanation for the assertion.
(4) Assertion is not true, but reason is true.
Ans. (2)
With increasing in temperature, the pH of the water will decrease.

The dissociation of water is an endothermic process.

Q.5. The Ksp for the following dissociation is 1.6 × 10⁻⁵
PbCl₂ (s) ⇌ Pb²⁺ (aq) 2Cl^- (aq)
Which of the following choices is correct for a mixture of 300 mL 0.134 M Pb(NO₃)₂ and 100 mL 0.4 M NaCl?    (2020)
(1) Not enough data provided
(2) Q < K_sp
(3) Q > K_sp
(4) Q = K_sp
Ans. (3)
Given,
K_sp (PbCl₂) = 1.6 x 10^-5
The concentration of Pb2+ from the given solution of Pb(NO₃)₂

The concentration of Cl^– from the given solution of NaCl

Thus, for the reaction

The ionic product is

Thus, Q > K_sp.

Q.6. The solubility product of Cr(OH)₃ at 298 K is 6.0 × 10⁻³¹. The concentration of hydroxide ions in a saturated solution of Cr(OH)₃ will be    (2020)
(1) (2.22 x 10^-31)^1/4
(2) (18 x 10^-31)^1/4
(3) (18 x 10^-31)^1/2
(4) (4.86 x 10^-29)^1/4
Ans. (2)
Given, K_sp = 6.0 x 10^-31


⇒ K_sp = S x (3S)³ = 27S⁴ ...(i)
Substituting the value in Eq. (i), we get

 ...(ii)
The concentration of hydroxide ions in a saturated solution
[OH^-] = 3S ...(iii)
Substituting the value from Eq. (2) in Eq. (3), we get

⇒ [OH^-] = (18.0 x 10^-31)^1/4

Q.7. In the figure shown below reactant A (represented by square) is in equilibrium with product B (represented by circle). The equilibrium constant is    (2020)

(1) 4
(2) 8
(3) 1
(4) 2
Ans. (4)
From the given figure,
Equilibrium constant (Keq) =  = 12/6 = 2

Q.8. The first and second ionization enthalpies of a metal are 4.96 and 4560 kJ mol⁻¹, respectively. How many moles of HCl and H₂SO₄, respectively, will be needed to react completely with 1 mol of the metal hydroxide?    (2020)
(1) 1 and 1
(2) 2 and 0.5
(3) 1 and 2
(4) 1 and 0.5
Ans. (4)
Since, the difference between first and second ionization enthalpies is extremely large, so, the metal must an alkali metal. For the completely neutralization of metal hydroxide with HCl and H₂SO₄.
MOH + HCl → MCl + H₂O
2MOH + H₂SO₄ → M₂SO₄ + 2H₂O
For 1 mol of MOH, 1 mol of HCl and 0.5 mol of H₂SO₄ is required.

Q.9. Consider the following reversible chemical reactions:

The relation between K₁ and K₂ is:    (2019)
(1) K₁K₂ = 1/3
(2) K₂ = K₁³
(3) K₂ = K₁^-3
(4) K₁K₂ = 3
Ans. (3)
Given:

The relation between K₁ and K₂ is K₂ = K₁^-3

Q.10. The values of K_p/K_c for the following reactions at 300 K are, respectively: (At 300 K, RT = 24.62 dm³ atm mol^-1)
N₂(g) + O₂(g) ⇌ 2NO(g)
N₂O₂(g) ⇌ 2NO₂(g)
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)    (2019)
(1) 1, 24.62 dm³ atm mol^-1, 606.0 dm⁶ atm² mol^-2
(2) 1, 24.62 dm³ atm mol^-1, 65 x 10^-3 dm^-6 atm^-2 mol²
(3) 1,4.1 x 10^-2 dm^-3 atm^-1 mol, 606 dm⁶ atm² mol^-2
(4) 24.62 dm³ atm mol^-1, 606.0 dm⁶ atm² mol^-2, 1.65 x 10^-3 dm^-6 atm^-2 mol²
Ans. (2)

Δn_g = No. of gaseous moles of products - No. of gaseous moles of reactants



 

Q.11. 5.1 g NH₄SH is introduced in 3.0 L evacuated flask at 327°C, 30% of the solid NH₄SH decomposed to NH₃ and H₂S as gases. The K_p of the reaction at 327°C is (R = 0.082 L atm mol^-1 K^-1, molar mass of S = 32 g mol^-1, molar mass of N = 14 g mol^-1)    (2019)
(1) 0.242 x 10^-4 atm²
(2) 1 x 10^-4 atm²
(3) 4.9 x 10^-3 atm²
(4) 0.242 atm²
Ans. (4)
Concerned reaction:
NH₄SH → NH₃(g) + H₂S (g)
Initial moles = 5.1/51 = 0.1 mol
Moles at equillibrium

∴

Q.12. Consider the reaction
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
The equilibrium constant of the above reaction is K_p. lf pure ammonia is left to dissociate, the partial pressure of ammonia at equilibrium is given by (Assume that P_NH3 <<P_total at equilibrium)    (2019)
(1)
(2)
(3)
(4)
Ans. (1)




Q.13. In a chemical reaction,  the initial concentration of B was 1.5 times of the concentration of A, but the equilibrium concentrations of A and B were found to be equal. The equilibrium constant (K) for the above chemical reaction is:    (2019)
(1) 4
(2) 16
(3) 1/4
(4) 1
Ans. (1)

⇒ x = 1
∴ [C] = 2, [D] = 1, [A] = 1, [B] = 1
∴

Q.14. Two solids dissociate as follows
A(s) → B(g) + C(g); K_P1 = x atm² 
D(s) → C(g) + E(g); K_P2 = y atm²
The total pressure when both the solids dissociate simultaneously is:    (2019)
(1)
(2)
(3) (x + y)atm
(4) x² + y² atm
Ans. (2)




Q.15. For the following reactions, equilibrium constants are given:

The equilibrium constant for the reaction,    (2019)

(1) 10¹⁵⁴
(2) 10¹⁸¹
(3) 10²⁵
(4) 10⁷⁷
Ans. (3)

To get equation (iii) follow (ii) - 2 (i),


Q.16. For the reaction,

Which of the following statement is INCORRECT?    (2019)
(1) The equilibrium constant is large suggestive of reaction going to completion and so no catalyst is required.
(2) The equilibrium will shift in forward direction as the pressure increases.
(3) The equilibrium constant decreases as the temperature increases.
(4) The addition of inert gas at constant volume will not affect the equilibrium constant.
Ans. (1)
Equilibrium constant has no relation with catalyst. Catalyst only affects the rate of the reaction.
Catalyst V₂O₅ in the given reaction, is used to speed up the reaction.

Q.17. In which one of the following equilibria, K_p ≠ K_c?    (2019)
(1) 2C(s) + O₂(g) ⇌ 2C0(g)
(2) 2HI(g) ⇌ H₂(g) + I₂(g)
(3) NO₂(g) + SO₂(g) ⇌ NO(g) + SO₃(g)
(4) 2NO(g) ⇌ N₂(g) + O₂(g)
Ans. (1)
We know that,



Q.18. 20 mL of 0.1 M H₂SO₄ solution is added to 30 mL of 0.2 M NH₄OH solution. The pH of the resultant mixture is: [pK_b of NH₄OH = 4.7].    (2019)
(1) 522
(2) 9.0
(3) 5.0
(4) 9.4
Ans. (2)
milli mol of H₂SO₄ = 20 x 0.1 = 2
milli mol of NH₄OH = 30 x 0.2 = 6
H₂SO₄ + 2NH₄OH → (NH4)₂SO₄+ 2H₂O


= 4.7 + log 2 = 5
pH= 14 - pOH
pH = 14 - 5 = 9

Q.19. For the equilibrium
 the value of ΔG° at 298 K is approximately:    (2019)
(1) 100 kJ mol^-1 
(2) -80 kJ mol^-1 
(3) 80 kJ mol^-1 
(4) -100 kJ mol^-1
Ans. (3)
ΔG = ΔG° + RT In Q
At equilibrium; ΔG = 0 and Q = K_eq 
⇒ ΔG° = - 2.303 RT log K_w 
= -2.303 x 8.314 x 298 x log 10^-14 
= 79.9 kJ/mol ≈ 80 kJ/mol

Q.20. If K_sp of Ag₂CO₃ is 8 x 10^-12, the molar solubility of Ag₂CO₃ in 0.1 M AgNO₃ is:    (2019)
(1) 8 x 10^-12M
(2) 8 x 10^-11 M
(3) 8 x 10^-10 M
(4) 8 x 10^-13 M
Ans. (3)
As AgNO₃ dissociates completely,
therefore in 0.1 M AgNO₃ solution, [Ag⁺] = 0.1 M



Q.21. If solubility product of Zr₃(PO₄)₄ is denoted by K_sp and its molar solubility is denoted by S, then which of the following relation between S and K_sp is correct?    (2019)
(1)
(2)
(3)
(4)
Ans. (2)


Q.22. In an acid base titration, 0.1 M HCI solution was added to the NaOH solution of unknown strength. Which of the following correctly shows the change of pH of the titration mixture in this experiment?    (2019)
 



(1) (B)
(2) (A)
(3) (C)
(4) (D)
Ans. (2)
Graph A and B, both represents the titration curve between strong acid and strong base, i.e., HCI and NaOH but, the pH of NaOH is more than 7 and during the titration it decreases, so graph (A) is correct.

Q.23. Consider the following statements    (2019)
(a) The pH of a mixture containing 400 mL of 0.1 M H₂SO₄ and 400 mL of 0.1 M NaOH will be approximately 1.3.
(b) Ionic product of water is temperature dependent.
(c) A monobasic acid with K_a-10^-5 has a pH = 5. The degree of dissociation of this acid is 50%.
(d) The Le Chatelier’s principle is not applicable to common-ion effect.
The correct statements are :
(1) (a) (b) and (d)
(2) (a) (b) and (c)
(3) (b) and (c)
(4) (a) and (b)
Ans. (2)

(b) Ionic product of water increases with increase in temperature because ionisation of water is endothermic.



Q.24. The pH of a 0.02 M NH₄Cl solution will be [given K_b(NH₄OH)=10^-5 and log 2 = 0.301]    (2019)
(1) 2.65
(2) 4.35
(3) 4.65
(4) 5.35
Ans. (4)

pH = 5.35

Q.25. What is the molar solubility of Al(OH)₃ in 0.2 M NaOH solution? Given that, solubility product of Al(OH)₃ = 2.4 x 10^-24:    (2019)
(1) 3 x 10^-19
(2) 12 x 10^-21
(3) 3 x 10^-22
(4) 12 x 10^-23
Ans. (3)
Let the solubility of Al(OH)₃ in 0.2M NaOH solution be s.
Then,




Q.26. The molar solubility of Cd(OH)₂ is 1.84 x 10^-5 M in water. The expected solubility of Cd(OH)₂ in a buffer solution of pH= 12 is:    (2019)
(1) 1.84 x 10^-9 M
(2)
(3) 6.23 x 10^-11 M
(4) 2.49 x 10^-10 M
Ans. (4)

Solubility in buffer solution having pH = 12
[OH^-] = 10^-2
 

Q.27. An aqueous solution contains 0.10 M H₂S and 0.20 M HCl. If the equilibrium constants for the format ion of HS^- from H₂S is 1.0 x 10^-7 and that of S^2- from HS^- ions is 1.2 x 10^-13 then the concentration of S^2- ions in aqueous solution is:     (2018)
(1) 5 x 10^-8 
(2) 3 x 10^-20 
(3) 6 x 10^-21 
(4) 5 x 10^-19 
Ans. (2)



Q.28. An aqueous solution contains an unknown concentration of Ba²⁺. When 50 mL of a 1M solution of Na₂SO₄ is added, BaSO₄ just begins to precipitate. The final volume is 500 mL. The solubility product of BaSO₄ is 1 x 10^-10. What is the original concentration of Ba²⁺ ?      (2018)
(1) 5 x 10^-9 M 
(2) 2 x 10^-9 M 
(3) 1.1 x 10^-9 M 
(4) 1.0 x 10^-10 M 
Ans. (3)




Q.29. Which of the following are Lewis acids?      (2018)
(1) PH₃ and BCl₃ 
(2) AlCl₃ and SiCl₄ 
(3) PH₃ and SiCl₄ 
(4) BCl₃ and AlCl₃ 
Ans. (4)
Both BCl₃ and AlCl₃ are Lewis acids as both ‘B’ and ‘Al’ has vacant p-orbitals. SiCl₄ is also a Lewis acid as silicon atom has vacant 3d-orbital.Therefore,both b and d options are possible. 

Q.30. Which of the following salts is the most basic in aqueous solution?      (2018)
(1) Al(CN)₃ 
(2) CH₃COOK 
(3) FeCl₃ 
(4) Pb(CH₃COO)₂ 
Ans. (2)
CH₃COOK is a salt of weak acid and strong base. Hydrolysis of potassium acetate gives strong base KOH

Q.31. In which of the following reactions, an increase in the volume of the container will favour the formation of  products?    (2018)
(1) 3O₂(g) ⇌ 2O₃(g) 
(2) 2NO₂(g) ⇌ 2NO(g) + O₂(g) 
(3) 4NH₃(g) + 5O₂(g) ⇌ 4NO(g) + 6H₂O(I) 
(4) H₂(g) + I₂(g) ⇌ 2HI(g) 
Ans. (2)
Volume increases P decreases reaction proceed in that direction where number of gaseous moles increases.


Q.32. The minimum volume of water required to dissolve 0.1g lead (II) chloride to get a saturated solution (K_sp of PbCl₂ = 3.2 x 10^-8; atomic mass of Pb= 207 u) is:    (2018)
(1) 0.18 L 
(2) 0.36 L 
(3) 17.98 L 
(4) 1.798 L 
Ans. (1)



Q.33. For which of the following reactions, ΔH is equal to ΔU?    (2018)
(1) N₂(g) + 3H₂(g) → 2NH₃(g) 
(2) 2NO₂(g) → N₂O₄(g) 
(3) 2SO₂(g) + O₂(g) → 2SO₃(g) 
(4) 2HI(g) → H₂(g) + I₂(g) 
Ans. (4)
ΔH = ΔU + Δn_gRT.  
[If Δn_g = 0 then ΔH =ΔU] 

Q.34. At 320 K, a gas A₂ is 20 % dissociated to A(g). The standard free energy change at 320 K and 1 atm in J mol^–1 is approximately : (R = 8.314 JK^–1 mol^–1 ; ln 2 = 0.693 ; ln 3 = 1.098)    (2018)
(1) 1844
(2) 2068
(3) 4281
(4) 4763
Ans. (3)


ΔGº = –2.303 × 8.314 × 320 log₁₀ 0.2 = 4281 J/mole 

Q.35. The gas phase reaction 2NO₂(g) → N₂O₄(g) is an exothermic reaction. The decomposition of N₂O₄, in equilibrium mixture of NO₂(g) and N₂O₄(g), can be increased by:    (2018)
(1) addition of an inert gas at constant pressure. 
(2) lowering the temperature 
(3) increasing the pressure 
(4) addition of an inert gas at constant volume. 
Ans. (1)
2NO₂(g) → N₂O₄(g) ΔH = (–) 
By addition of an inert gas at constant pressure, volume increases, so reaction moving in backward direction and decomposition of N₂O₄ increases. 

Q.36. pK_a of a weak acid (HA) and pK_b of a weak base(BOH) are 3.2 and 3.4, respectively, The pH of their salt (AB) solution is    (2017)
(1) 7.2
(2) 6.9
(3) 7.0
(4) 1.0
Ans. 2


= 6.9 

Q.37. In the following reactions, ZnO is respectively acting as a/an    (2017)
(a) ZnO + Na₂O → Na₂ZnO₂
(b) ZnO + CO₂ → ZnCO₃ 
(1) Base and acid 
(2) Base and base 
(3) Acid and acid 
(4) Acid and base 
Ans.  (4)
In (a), ZnO acts as acidic oxide as Na₂ 
O is basic oxide. 
In (b), ZnO acts as basic oxide as CO₂  is acidic oxide. 

Q.38. Addition of sodium hydroxide solution to a weak acid (HA) results in a buffer of pH 6. If ionisation constant of HA is 10^–5, the ratio of salt to acid concentration in the buffer solution will be:    (2017)
(1) 10 : 1
(2) 4 : 5
(3) 5 : 4
(4) 1 : 10
Ans. (1)
HA ⇌ H⁺ + A^-
(Unionised, weak acid and common ion effect)
HA + NaOH → NaA + H₂O


Q.39. 50 mL of 0.2 M ammonia solution is treated with 25 mL of 0.2 M HCl. If pK_b  of ammonia solution is 4.75, the pH of the mixture will be:    (2017)
(1) 8.25
(2) 9.25
(3) 3.75
(4) 4.75
Ans. (4)
NH3 + HCI → NH₄CI
moles of HCI = 0.2 M x 25 x  10^-3 L = 0.005 moles HCI (total consumed)
moles of NH₃ = 0.2 M x 50 x 10^-3 L = 0.01 moles HCI
excess NH₃ = 0.01 - 0.005 = 0.005 moles
1 mole ammonia = 1 mole NH₄CI
0.005 NH₃ = 0.005 NH₅CI

pOH = 4.75
pH = 14 - pOH ⇒ pH = 4.75

Q.40. The following reaction occurs in the Blast Furnace where iron ore is reduced to iron metal:
Fe₂O₃(s) + 3CO(g) ⇌ 2Fe(I) + 3CO₂(g)
Using the Le Chatelier’s principle, predict which one of the following will not disturb the equilibrium?    (2017)
(1) Addition of CO₂
(2) Removal of CO₂
(3) Addition of Fe₂O₃
(4) Removal of CO
Ans. (3)


Q.41. The equilibrium constant at 298 K for a reaction A + BC + D is 100. If the initial concentration of all the four species were 1M each, then equilibrium concentration of D (in mol L^-1) will be:    (2016)
(1) 0.182
(2) 0.818
(3) 1.818
(4) 1.182
Ans. (3)



Q.42. For the reaction, A(g) + B(g) → C(g) + D(g), ΔH⁰ and ΔS⁰ are, respectively, -29.8kJ mol^-1 and -0.100 kJ K^-1 mol^-1 at 298 K. The equilibrium constant for the reaction at 298 K is:    (2016)
(1) 1.0 x 10^-10
(2) 10
(3) 1
(4) 1.0 x  10¹⁰
Ans. (3)
ΔG⁰ = ΔH⁰ - T.ΔS⁰
= -29.8 + 298 x (0.1)
= -29.8 + 29.8
∵ ΔG⁰ = 0
apply relation between ΔG⁰ & K_eq
ΔG⁰ = -RT ln K_eq
ln K_eq = 1

Q.43. A solid XY kept in an evacuated sealed container undergoes decomposition to form a mixture of gases X and Y at temperature T. The equilibrium pressure is 10 bar in this vessel. K_p for this reaction is:     (2016)
(1) 25
(2) 5
(3) 10
(4) 100
Ans. (1)

Total pressure = 2P = 10 bar
⇒ P = 5
Now, K_P = (P_X)(P_Y) = P² = 25