MCQs, Fill in the Blanks, True/False, Assertion-Reason, Match the Following & Short Answer Questions

SECTION A: Multiple Choice Questions (MCQs)

1. Equilibrium in a reversible reaction is:

A) A state where reaction stops
B) A state where forward and backward rates become equal
C) A state where only products are present
D) A state where only reactants are present

Answer: B

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2. Chemical equilibrium is:

A) Static in nature
B) Dynamic in nature
C) Possible only in open systems
D) Independent of temperature

Answer: B

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3. At equilibrium:

A) Concentration becomes zero
B) Reaction completely stops
C) Concentration remains constant
D) Products disappear

Answer: C

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4. Physical equilibrium involves:

A) Formation of new substances
B) Chemical reaction only
C) Change in physical state
D) Nuclear change

Answer: C

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5. Which condition is necessary for establishing equilibrium?

A) Open container
B) Closed system
C) High temperature only
D) Catalyst only

Answer: B

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6. Vapour pressure is the pressure exerted by:

A) Liquid molecules only
B) Vapour molecules at equilibrium
C) Solid particles
D) Atmospheric gases

Answer: B

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7. Sublimation is the conversion of:

A) Solid → Liquid
B) Liquid → Gas
C) Solid → Gas
D) Gas → Liquid

Answer: C

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8. In a saturated solution:

A) Solute continues dissolving forever
B) Dissolution rate equals crystallisation rate
C) No solute is present
D) Water evaporates completely

Answer: B

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9. Henry’s law explains:

A) Acid strength
B) Gas solubility in liquids
C) pH calculation
D) Salt hydrolysis

Answer: B

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10. For the reaction:

$$aA+bB\rightleftharpoons cC+dD$$aA+bB⇌cC+dD

The equilibrium constant is:

A)$$\frac{A+B}{C+D}$$C+DA+B​

B)$$\frac{[C]^c[D]^d}{[A]^a[B]^b}$$[A]a[B]b[C]c[D]d​

C)$$\frac{[A]^a[B]^b}{[C]^c[D]^d}$$[C]c[D]d[A]a[B]b​

D)$$[C+D]-[A+B]$$[C+D]−[A+B]

Answer: B

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Equilibrium Constant MCQs

11. The value of equilibrium constant depends on:

A) Pressure only
B) Concentration only
C) Temperature
D) Catalyst

Answer: C

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12. If K is very large, the equilibrium mixture contains:

A) Mostly reactants
B) Mostly products
C) Equal reactants and products always
D) No products

Answer: B

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13. When a reaction is reversed, the new equilibrium constant becomes:

A) K²
B) K+1
C) 1/K
D) K−1

Answer: C

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14. Pure solids are omitted from equilibrium expressions because:

A) They do not exist
B) Their concentration remains constant
C) They are gases
D) They react faster

Answer: B

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15. The relation between $K_p$Kp​ and $K_c$Kc​ is:

A)$$K_p=K_c(RT)^{\Delta n}$$Kp​=Kc​(RT)Δn

B)$$K_p=K_c+RT$$Kp​=Kc​+RT

C)$$K_p=K_c/RT$$Kp​=Kc​/RT

D)$$K_p=K_c-RT$$Kp​=Kc​−RT

Answer: A

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Le Chatelier Principle MCQs

16. Increasing pressure shifts equilibrium towards:

A) More gaseous molecules
B) Fewer gaseous molecules
C) Solids only
D) Liquids only

Answer: B

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17. A catalyst:

A) Changes equilibrium constant
B) Changes equilibrium position
C) Speeds up equilibrium attainment
D) Stops reverse reaction

Answer: C

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18. Temperature affects:

A) Only concentration
B) Only pressure
C) Equilibrium constant
D) Catalyst activity

Answer: C

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Ionic Equilibrium MCQs

19. A strong electrolyte:

A) Does not ionise
B) Completely ionises
C) Partially ionises
D) Forms no ions

Answer: B

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20. According to Arrhenius theory, an acid produces:

A) OH⁻
B) H⁺
C) Electrons
D) Salt only

Answer: B

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21. According to Brønsted-Lowry theory, a base is:

A) Proton donor
B) Proton acceptor
C) Electron acceptor
D) Salt producer

Answer: B

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22. Lewis acid accepts:

A) Proton
B) Electron pair
C) Neutron
D) Hydroxide ion

Answer: B

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23. The value of $K_w$Kw​ at 25°C is:

A) $10^{-7}$10−7
B) $10^{-10}$10−10
C) $10^{-14}$10−14
D) $10^{-1}$10−1

Answer: C

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24. pH of neutral water at 25°C is:

A) 0
B) 5
C) 7
D) 14

Answer: C

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25. Buffer solution resists change in:

A) Temperature
B) Pressure
C) pH
D) Volume

Answer: C

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SECTION B: Fill in the Blanks

1. Equilibrium is a ______ process.

Answer: dynamic

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2. At equilibrium, forward rate is ______ to backward rate.

Answer: equal

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3. Equilibrium can be established only in a ______ system.

Answer: closed

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4. The equilibrium constant based on concentration is called ______.

Answer: Kc

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5. The equilibrium constant based on pressure is called ______.

Answer: Kp

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6. The value of K changes with change in ______.

Answer: temperature

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7. Pure solids are not included in equilibrium expressions because their concentration remains ______.

Answer: constant

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8. The relation between pH and pOH is:

$$pH+pOH=\_\_\_\_$$pH+pOH=____

Answer: 14

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9. $K_a$Ka​ represents the strength of a ______.

Answer: acid

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10. $K_b$Kb​ represents the strength of a ______.

Answer: base

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11. A solution that maintains nearly constant pH is called a ______ solution.

Answer: buffer

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12. The equilibrium constant for sparingly soluble salts is called ______.

Answer: solubility product

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13. The formula of ionic product of water is ______.

Answer: Kw=[H+][OH−]K_w=[H^+][OH^-]Kw​=[H+][OH−]

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14. Increasing temperature shifts an exothermic reaction towards the ______ direction.

Answer: backward

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15. A catalyst changes the ______ of reaction but not equilibrium position.

Answer: rate

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SECTION C: True or False

1. Equilibrium means reactions stop completely.

False

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2. Equilibrium is possible in an open container.

False

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3. $K$K depends on temperature.

True

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4. Catalyst changes the value of equilibrium constant.

False

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5. Solids are included in all equilibrium expressions.

False

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6. pH measures hydrogen ion concentration.

True

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7. Strong electrolytes completely ionise.

True

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8. Buffer solutions resist pH changes.

True

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9. Pressure affects only gaseous equilibrium.

True

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10. $K_aK_b=K_w$Ka​Kb​=Kw​

True

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SECTION D: Assertion–Reason Questions

1.

Assertion: Equilibrium is dynamic.

Reason: Forward and backward reactions continue at equal rates.

A) Both true and reason explains assertion
B) Both true but reason does not explain
C) Assertion true, reason false
D) Both false

Answer: A

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2.

Assertion: Catalyst does not change equilibrium position.

Reason: Catalyst increases rates of both forward and reverse reactions equally.

Answer: A

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3.

Assertion: Increasing pressure favours ammonia formation in Haber process.

Reason: Product side has fewer gas molecules.

Answer: A

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4.

Assertion: pH of pure water is 7.

Reason: Hydrogen and hydroxide ion concentrations are equal.

Answer: A

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SECTION E: Match the Following

Column A	Column B
1. $K_a$Ka​	a. Base strength
2. $K_b$Kb​	b. Acid strength
3. $K_w$Kw​	c. Water ionisation
4. $K_{sp}$Ksp​	d. Solubility

Answers:

1 → b
2 → a
3 → c
4 → d

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SECTION F: Very Short Answer Questions

1. What is dynamic equilibrium?

Answer:
A state where forward and reverse reactions continue at equal rates.

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2. Define equilibrium constant.

Answer:
It is the ratio of product concentration to reactant concentration at equilibrium.

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3. What happens when Q = K?

Answer:
The reaction is at equilibrium.

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4. What is a strong electrolyte?

Answer:
An electrolyte that completely ionises in solution.

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5. What is a buffer?

Answer:
A solution that resists change in pH.

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SECTION G: Short Answer Questions

1. State Le Chatelier’s principle.

Answer:
When equilibrium is disturbed, the system shifts in a direction that reduces the effect of the disturbance.

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2. Why are catalysts not included in equilibrium constant expressions?

Answer:
Because catalysts change reaction rates but do not change equilibrium concentrations.

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3. Explain common ion effect.

Answer:
The decrease in ionisation of a weak electrolyte due to addition of a common ion is called common ion effect.

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4. Why are pure solids ignored in $K_c$Kc​?

Answer:
Because their concentration remains constant.

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5. Write the formula of Henderson-Hasselbalch equation.

Answer:$$pH=pK_a+\log\frac{Salt}{Acid}$$pH=pKa​+logAcidSalt​

Part 2: Advanced MCQs + Numerical Questions + HOTS + Board Pattern Questions

Part 2: Advanced MCQs, Numerical MCQs, HOTS & Board Pattern Questions

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SECTION A: Advanced MCQs

1. In a reversible reaction, equilibrium is established when:

A) Reactants completely convert into products
B) Products completely convert into reactants
C) Forward and backward reaction rates become equal
D) Concentration of reactants becomes zero

Answer: C) Forward and backward reaction rates become equal

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2. At equilibrium, which statement is correct?

A) Reaction stops completely
B) Concentration of reactants and products becomes equal
C) Concentrations remain constant with time
D) Only products are present

Answer: C) Concentrations remain constant with time

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3. For the reaction:

$$N_2(g)+3H_2(g)\rightleftharpoons2NH_3(g)$$N2​(g)+3H2​(g)⇌2NH3​(g)

The expression for $K_c$Kc​ is:

A)$$\frac{[NH_3]}{[N_2][H_2]}$$[N2​][H2​][NH3​]​

B)$$\frac{[NH_3]^2}{[N_2][H_2]^3}$$[N2​][H2​]3[NH3​]2​

C)$$\frac{[N_2][H_2]^3}{[NH_3]^2}$$[NH3​]2[N2​][H2​]3​

D)$$[N_2][H_2][NH_3]$$[N2​][H2​][NH3​]

Answer: B

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4. The value of equilibrium constant changes when:

A) Concentration changes
B) Pressure changes
C) Catalyst is added
D) Temperature changes

Answer: D) Temperature changes

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5. If KcK_cKc​ is very high, it indicates:

A) Reaction favours reactants
B) Reaction favours products
C) Reaction stops
D) No equilibrium exists

Answer: B) Reaction favours products

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6. Which of the following does not affect equilibrium position?

A) Temperature
B) Pressure
C) Concentration
D) Catalyst

Answer: D) Catalyst

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7. For the reaction:

$$H_2+I_2\rightleftharpoons2HI$$H2​+I2​⇌2HI

The value of Δn is:

A) 2
B) 1
C) 0
D) -2

Answer: C) 0

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8. When Δn = 0, the relation between KpK_pKp​ and KcK_cKc​ is:

A)$$K_p>K_c$$Kp​>Kc​

B)$$K_p<K_c$$Kp​<Kc​

C)$$K_p=K_c$$Kp​=Kc​

D) Cannot be predicted

Answer: C

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9. Pure liquids are not included in equilibrium constant expressions because:

A) They do not react
B) Their concentration remains constant
C) They are gases
D) They have zero concentration

Answer: B

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10. Which of the following is a heterogeneous equilibrium?

A)$$H_2+I_2\rightleftharpoons2HI$$H2​+I2​⇌2HI

B)$$N_2+3H_2\rightleftharpoons2NH_3$$N2​+3H2​⇌2NH3​

C)$$CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)$$CaCO3​(s)⇌CaO(s)+CO2​(g)

D)$$HCl\rightleftharpoons H^++Cl^-$$HCl⇌H++Cl−

Answer: C

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SECTION B: Equilibrium Constant Based MCQs

11. For the reaction:

$$A+B\rightleftharpoons C$$A+B⇌C

If equilibrium concentration of A, B and C are 2M, 3M and 6M respectively, $K_c$Kc​ is:

A) 1
B) 2
C) 3
D) 6

Solution:$$K_c=\frac{[C]}{[A][B]}$$Kc​=[A][B][C]​ $$K_c=\frac6{2\times3}=1$$Kc​=2×36​=1

Answer: A) 1

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12. For the reaction:

$$2SO_2+O_2\rightleftharpoons2SO_3$$2SO2​+O2​⇌2SO3​

The expression for $K_c$Kc​ is:

A)$$\frac{[SO_3]^2}{[SO_2]^2[O_2]}$$[SO2​]2[O2​][SO3​]2​

B)$$\frac{[SO_2]^2[O_2]}{[SO_3]^2}$$[SO3​]2[SO2​]2[O2​]​

C)$$\frac{[SO_3]}{[SO_2][O_2]}$$[SO2​][O2​][SO3​]​

D)$$[SO_3]^2$$[SO3​]2

Answer: A

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13. If equilibrium constant for a reaction is 100, the equilibrium constant for reverse reaction will be:

A) 100
B) 10
C) 0.01
D) 1

Answer: C

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14. When the coefficients of a balanced chemical equation are doubled, the equilibrium constant becomes:

A) K/2
B) 2K
C) K²
D) √K

Answer: C

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SECTION C: Le Chatelier Principle Questions

15. For Haber process:

$$N_2+3H_2\rightleftharpoons2NH_3+Heat$$N2​+3H2​⇌2NH3​+Heat

Increasing pressure will:

A) Shift equilibrium left
B) Shift equilibrium right
C) Have no effect
D) Stop reaction

Answer: B

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16. For an exothermic reaction, increasing temperature causes:

A) Forward shift
B) Backward shift
C) No change
D) Catalyst action

Answer: B

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17. Addition of reactants to an equilibrium system causes:

A) Shift towards reactants
B) Shift towards products
C) No change
D) Reaction stops

Answer: B

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18. A catalyst increases equilibrium rate because it:

A) Increases product concentration
B) Decreases activation energy
C) Changes equilibrium constant
D) Changes temperature

Answer: B

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SECTION D: Ionic Equilibrium MCQs

19. The ionisation of a weak acid is represented by:

A)$$HA\rightarrow H^++A^-$$HA→H++A−

B)$$HA\rightleftharpoons H^++A^-$$HA⇌H++A−

C)$$HA\rightarrow H_2O$$HA→H2​O

D)$$HA\rightarrow A+H_2$$HA→A+H2​

Answer: B

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20. The value of KaK_aKa​ indicates:

A) Base strength
B) Acid strength
C) Salt solubility
D) Water concentration

Answer: B

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21. A solution with pH = 3 is:

A) Neutral
B) Basic
C) Acidic
D) Salt solution

Answer: C

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22. At 25°C, neutral water has:

A)$$[H^+]=10^{-7}M$$[H+]=10−7M

B)$$[H^+]=10^{-3}M$$[H+]=10−3M

C)$$[OH^-]=10^{-3}M$$[OH−]=10−3M

D)$$pH=14$$pH=14

Answer: A

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23. Which pair forms an acidic buffer?

A) HCl + NaCl
B) NaOH + NaCl
C) CH₃COOH + CH₃COONa
D) HNO₃ + KNO₃

Answer: C

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24. The formula of Henderson-Hasselbalch equation is:

A)$$pH=pK_a+\log\frac{Salt}{Acid}$$pH=pKa​+logAcidSalt​

B)$$pH=pK_b+\log\frac{Acid}{Salt}$$pH=pKb​+logSaltAcid​

C)$$pH=-\log K_w$$pH=−logKw​

D)$$pH=pOH$$pH=pOH

Answer: A

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SECTION E: Numerical & Concept-Based Questions

25. Calculate pH of a solution having hydrogen ion concentration:

$$[H^+]=10^{-4}M$$[H+]=10−4M

Solution:$$pH=-\log(10^{-4})$$pH=−log(10−4) $$pH=4$$pH=4

Answer: pH = 4

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26. Calculate pOH if pH = 5.

Solution:$$pH+pOH=14$$pH+pOH=14 $$5+pOH=14$$5+pOH=14 $$pOH=9$$pOH=9

Answer: pOH = 9

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27. Calculate hydroxide ion concentration if:

$$pOH=3$$pOH=3

Solution:$$[OH^-]=10^{-pOH}$$[OH−]=10−pOH $$=10^{-3}M$$=10−3M

Answer: 10−3M10^{-3}M10−3M

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28. If KaK_aKa​ value of acid A is greater than acid B, which acid is stronger?

Answer: Acid A is stronger because higher KaK_aKa​ indicates greater ionisation.

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29. Why does dilution increase ionisation of weak electrolytes?

Answer: Dilution shifts equilibrium towards ions according to Le Chatelier’s principle.

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30. Why does adding sodium acetate decrease ionisation of acetic acid?

Answer: Due to common ion effect caused by acetate ions.

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SECTION F: HOTS Questions

31. Why is equilibrium called a dynamic state?

Answer:
Because forward and reverse reactions continue continuously at equal rates.

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32. Why does a catalyst not change equilibrium composition?

Answer:
Because it increases the rates of both forward and backward reactions equally.

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33. Why does increasing pressure favour ammonia formation in Haber process?

Answer:
Because ammonia formation decreases the number of gas molecules.

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34. Why are solids ignored in equilibrium constant expressions?

Answer:
Because their concentration remains constant.

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35. Why does temperature change equilibrium constant but not concentration change?

Answer:
Because equilibrium constant depends only on temperature.

Part 3: Fill in the Blanks, True/False, Assertion–Reason & Case-Based Questions

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SECTION A: Fill in the Blanks

Q1. Equilibrium in a reversible reaction is a ______ process.

Ans: Dynamic

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Q2. At equilibrium, the rate of forward reaction is ______ to the rate of backward reaction.

Ans: Equal

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Q3. Equilibrium can be established only in a ______ system.

Ans: Closed

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Q4. The equilibrium constant based on concentration is represented by ______.

Ans: KcK_cKc​

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Q5. The equilibrium constant based on pressure is represented by ______.

Ans: KpK_pKp​

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Q6. The value of equilibrium constant depends only on ______.

Ans: Temperature

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Q7. In equilibrium constant expression, powers are equal to the ______ coefficients.

Ans: Stoichiometric

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Q8. Pure solids are not included in equilibrium expressions because their concentration remains ______.

Ans: Constant

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Q9. The reaction quotient is represented by ______.

Ans: Q

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Q10. When Q = K, the system is at ______.

Ans: Equilibrium

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Q11. If Q < K, the reaction proceeds in the ______ direction.

Ans: Forward

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Q12. If Q > K, the reaction proceeds in the ______ direction.

Ans: Backward

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Q13. The principle used to predict the effect of changes on equilibrium is called ______.

Ans: Le Chatelier’s principle

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Q14. Increasing pressure shifts equilibrium towards the side having ______ gaseous molecules.

Ans: Fewer

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Q15. A catalyst changes the ______ of a reaction.

Ans: Rate

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Q16. A catalyst does not change the ______ position.

Ans: Equilibrium

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Q17. The ionisation constant of an acid is represented by ______.

Ans: KaK_aKa​

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Q18. The ionisation constant of a base is represented by ______.

Ans: KbK_bKb​

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Q19. The ionic product of water is represented by ______.

Ans: KwK_wKw​

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Q20. At 25°C, the value of $K_w$Kw​ is ______.

Ans: 1.0×10−141.0\times10^{-14}1.0×10−14

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Q21. The pH of neutral water at 25°C is ______.

Ans: 7

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Q22. The formula of pH is ______.

Ans: pH=−log⁡[H+]pH=-\log[H^+]pH=−log[H+]

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Q23. The formula of pOH is ______.

Ans: pOH=−log⁡[OH−]pOH=-\log[OH^-]pOH=−log[OH−]

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Q24. The relation between pH and pOH is ______.

Ans: pH+pOH=14pH+pOH=14pH+pOH=14

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Q25. A solution that resists change in pH is called a ______.

Ans: Buffer solution

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Q26. Acetic acid and sodium acetate form an ______ buffer.

Ans: Acidic

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Q27. Ammonium hydroxide and ammonium chloride form a ______ buffer.

Ans: Basic

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Q28. The equilibrium constant for sparingly soluble salts is called ______.

Ans: Solubility product (KspK_{sp}Ksp​)

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Q29. Addition of a common ion decreases the ______ of a weak electrolyte.

Ans: Ionisation

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Q30. According to Arrhenius theory, acids produce ______ ions.

Ans: Hydrogen (H+H^+H+)

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SECTION B: True or False

Q1. Equilibrium means that the reaction stops completely.

Ans: False

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Q2. Equilibrium is possible only in a closed system.

Ans: True

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Q3. Forward and backward reactions continue at equilibrium.

Ans: True

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Q4. Concentrations of reactants and products become equal at equilibrium.

Ans: False

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Q5. Equilibrium constant changes with concentration.

Ans: False

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Q6. Temperature affects the value of equilibrium constant.

Ans: True

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Q7. Catalyst changes the equilibrium constant.

Ans: False

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Q8. Pressure affects only gaseous equilibrium.

Ans: True

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Q9. Pure solids are included in $K_c$Kc​ expressions.

Ans: False

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Q10. A large value of K indicates products are favoured.

Ans: True

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Q11. A small value of K indicates reactants are favoured.

Ans: True

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Q12. pH of acidic solution is greater than 7.

Ans: False

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Q13. Strong electrolytes completely ionise in water.

Ans: True

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Q14. Weak electrolytes completely ionise in water.

Ans: False

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Q15. Buffer solutions maintain constant pH.

Ans: Almost true (they resist change in pH)

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Q16. $K_aK_b=K_w$Ka​Kb​=Kw​ for conjugate acid-base pairs.

Ans: True

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Q17. Increasing temperature affects equilibrium constant.

Ans: True

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Q18. Adding a common ion increases ionisation of weak electrolyte.

Ans: False

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Q19. Lewis acids accept electron pairs.

Ans: True

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Q20. Lewis bases donate electron pairs.

Ans: True

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SECTION C: Assertion–Reason Questions

Q1.

Assertion: Chemical equilibrium is dynamic.

Reason: Forward and reverse reactions continue at equal rates.

A) Both Assertion and Reason are true and Reason explains Assertion
B) Both are true but Reason does not explain Assertion
C) Assertion true, Reason false
D) Assertion false, Reason true

Ans: A

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Q2.

Assertion: Equilibrium constant changes with temperature.

Reason: Temperature affects equilibrium composition.

Ans: A

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Q3.

Assertion: Catalyst does not change equilibrium position.

Reason: Catalyst increases both forward and reverse reaction rates equally.

Ans: A

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Q4.

Assertion: Increasing pressure favours ammonia formation.

Reason: Ammonia side has fewer gas molecules.

Ans: A

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Q5.

Assertion: Pure solids are excluded from equilibrium expressions.

Reason: Their concentrations remain constant.

Ans: A

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Q6.

Assertion: A solution with pH 2 is acidic.

Reason: Hydrogen ion concentration is high.

Ans: A

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Q7.

Assertion: Buffer solutions resist pH change.

Reason: They contain a weak acid/base and its conjugate salt.

Ans: A

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Q8.

Assertion: Strong acids have high $K_a$Ka​ values.

Reason: They ionise almost completely in water.

Ans: A

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SECTION D: Case-Based Questions

Case Study 1

A student studies the following reaction:$$N_2(g)+3H_2(g)\rightleftharpoons2NH_3(g)+Heat$$N2​(g)+3H2​(g)⇌2NH3​(g)+Heat

The reaction is used in the Haber process.

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Q1. What type of reaction is this?

Ans: Exothermic reversible reaction

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Q2. What happens when pressure is increased?

Ans: Equilibrium shifts towards ammonia formation.

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Q3. Why does pressure affect this reaction?

Ans: Because the number of gaseous molecules is different on both sides.

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Q4. What is the role of catalyst?

Ans: It increases the rate of reaching equilibrium.

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Case Study 2

A weak acid HA dissociates as:$$HA\rightleftharpoons H^++A^-$$HA⇌H++A−

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Q1. Write the expression for $K_a$Ka​.

Ans:$$K_a=\frac{[H^+][A^-]}{[HA]}$$Ka​=[HA][H+][A−]​

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Q2. What does a high $K_a$Ka​ value indicate?

Ans: Stronger acid

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Q3. What happens when sodium salt of A⁻ is added?

Ans: Ionisation of HA decreases due to common ion effect.

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Q4. Which principle explains this effect?

Ans: Le Chatelier’s principle

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Case Study 3

A solution has:$$[H^+]=10^{-5}M$$[H+]=10−5M

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Q1. Calculate pH.

Ans:$$pH=5$$pH=5

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Q2. Is the solution acidic or basic?

Ans: Acidic

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Q3. Calculate pOH.

Ans:$$pOH=14-5=9$$pOH=14−5=9

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SECTION E: One-Line Important Questions

Q1. What is the unit of equilibrium constant?

Ans: It depends on the reaction; it may have units or may be unitless.

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Q2. Which factor changes equilibrium constant?

Ans: Temperature

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Q3. Which factor does not change equilibrium position?

Ans: Catalyst

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Q4. Which theory explains electron pair transfer?

Ans: Lewis theory

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Q5. Which equation gives pH of buffer solution?

Ans: Henderson-Hasselbalch equation

Part 4: Long Answer Questions, Numerical Problems, HOTS & Board Pattern Questions

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SECTION A: Long Answer Questions (3–5 Marks)

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Q1. Explain the characteristics of chemical equilibrium.

Ans:

The important characteristics of chemical equilibrium are:

1. Equilibrium is dynamic in nature because forward and backward reactions continue continuously.
2. Rate of forward reaction becomes equal to rate of backward reaction.
3. Concentration of reactants and products remains constant with time.
4. Equilibrium can be established only in a closed system.
5. Equilibrium can be reached from either direction (starting with reactants or products).

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Q2. Explain the difference between homogeneous and heterogeneous equilibrium with examples.

Ans:

Homogeneous Equilibrium:

When all reactants and products are present in the same physical state.

Example:$$H_2(g)+I_2(g)\rightleftharpoons2HI(g)$$H2​(g)+I2​(g)⇌2HI(g)

All substances are gases.

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Heterogeneous Equilibrium:

When reactants and products are present in different physical states.

Example:$$CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)$$CaCO3​(s)⇌CaO(s)+CO2​(g)

Solid and gas phases are present.

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Q3. State Le Chatelier’s principle and explain the effect of concentration.

Ans:

Le Chatelier’s principle states:

“When a system at equilibrium is disturbed, it shifts in a direction that reduces the effect of the disturbance.”

For the reaction:$$H_2+I_2\rightleftharpoons2HI$$H2​+I2​⇌2HI

• Increasing concentration of $H_2$H2​ or $I_2$I2​ shifts equilibrium towards products.
• Increasing concentration of HI shifts equilibrium towards reactants.

The system tries to oppose the change.

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Q4. Explain the effect of pressure on gaseous equilibrium.

Ans:

Pressure affects only gaseous equilibrium.

According to Le Chatelier’s principle:

• Increasing pressure shifts equilibrium towards the side with fewer gas molecules.
• Decreasing pressure shifts equilibrium towards the side with more gas molecules.

Example:$$N_2+3H_2\rightleftharpoons2NH_3$$N2​+3H2​⇌2NH3​

Left side:

4 molecules of gas

Right side:

2 molecules of gas

Increasing pressure favours ammonia formation.

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Q5. Explain the effect of temperature on equilibrium.

Ans:

Temperature changes the equilibrium position and equilibrium constant.

Exothermic reaction:

$$Reactants\rightleftharpoons Products+Heat$$Reactants⇌Products+Heat

Increasing temperature shifts equilibrium backward.

Endothermic reaction:

$$Reactants+Heat\rightleftharpoons Products$$Reactants+Heat⇌Products

Increasing temperature shifts equilibrium forward.

Only temperature changes the value of equilibrium constant.

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SECTION B: Numerical Problems

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Q6. Calculate KcK_cKc​ for the reaction:

$$A+B\rightleftharpoons C$$A+B⇌C

At equilibrium:$$[A]=2M,\quad[B]=4M,\quad[C]=8M$$[A]=2M,[B]=4M,[C]=8M

Solution:

Formula:$$K_c=\frac{[C]}{[A][B]}$$Kc​=[A][B][C]​

Substitute values:$$K_c=\frac{8}{2\times4}$$Kc​=2×48​ $$K_c=1$$Kc​=1

Ans: Kc=1K_c=1Kc​=1

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Q7. Calculate pH of a solution having:

$$[H^+]=1\times10^{-3}M$$[H+]=1×10−3M

Solution:$$pH=-\log[H^+]$$pH=−log[H+] $$pH=-\log(10^{-3})$$pH=−log(10−3) $$pH=3$$pH=3

Ans: pH = 3

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Q8. Calculate pOH if pH is 11.

Solution:$$pH+pOH=14$$pH+pOH=14 $$11+pOH=14$$11+pOH=14 $$pOH=3$$pOH=3

Ans: pOH = 3

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Q9. Calculate hydrogen ion concentration of a solution having pH = 4.

Solution:$$pH=-\log[H^+]$$pH=−log[H+] $$[H^+]=10^{-pH}$$[H+]=10−pH $$[H^+]=10^{-4}$$[H+]=10−4

Ans:$$[H^+]=1\times10^{-4}M$$[H+]=1×10−4M

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Q10. Calculate hydroxide ion concentration when pOH = 5.

Solution:$$[OH^-]=10^{-pOH}$$[OH−]=10−pOH $$[OH^-]=10^{-5}M$$[OH−]=10−5M

Ans:$$[OH^-]=1\times10^{-5}M$$[OH−]=1×10−5M

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SECTION C: HOTS Questions

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Q11. Why does equilibrium constant not depend on initial concentration?

Ans:

Because equilibrium constant represents the ratio of equilibrium concentrations and depends only on temperature.

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Q12. Why does a catalyst not change the equilibrium constant?

Ans:

A catalyst increases the rate of both forward and reverse reactions equally. Therefore, the equilibrium position and equilibrium constant remain unchanged.

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Q13. Why does increasing pressure favour ammonia formation in Haber process?

Ans:

The reaction:$$N_2+3H_2\rightleftharpoons2NH_3$$N2​+3H2​⇌2NH3​

has fewer gas molecules on the product side.

Higher pressure favours the side with fewer molecules, so ammonia formation increases.

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Q14. Why is pure water neutral at 25°C?

Ans:

In pure water:$$[H^+]=[OH^-]=10^{-7}M$$[H+]=[OH−]=10−7M

Equal hydrogen and hydroxide ion concentrations make it neutral.

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Q15. Why does dilution increase ionisation of weak electrolytes?

Ans:

Dilution decreases ion concentration, so equilibrium shifts towards formation of more ions according to Le Chatelier’s principle.

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SECTION D: Board Pattern Questions

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Q16. Derive the relation between KpK_pKp​ and KcK_cKc​.

Ans:

For gaseous reaction:$$aA+bB\rightleftharpoons cC+dD$$aA+bB⇌cC+dD $$K_c=\frac{[C]^c[D]^d}{[A]^a[B]^b}$$Kc​=[A]a[B]b[C]c[D]d​

Using:$$PV=nRT$$PV=nRT

and concentration-pressure relation:$$K_p=K_c(RT)^{\Delta n}$$Kp​=Kc​(RT)Δn

where:$$\Delta n=\text{moles of gaseous products}-\text{moles of gaseous reactants}$$Δn=moles of gaseous products−moles of gaseous reactants

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Q17. Explain common ion effect with an example.

Ans:

Common ion effect is the decrease in ionisation of a weak electrolyte due to addition of a strong electrolyte containing a common ion.

Example:$$CH_3COOH\rightleftharpoons H^++CH_3COO^-$$CH3​COOH⇌H++CH3​COO−

Adding sodium acetate increases $CH_3COO^-$CH3​COO− concentration.

Equilibrium shifts backward and ionisation decreases.

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Q18. Explain buffer action of acidic buffer.

Ans:

An acidic buffer contains:

• Weak acid
• Salt of its conjugate base

Example:$$CH_3COOH+CH_3COONa$$CH3​COOH+CH3​COONa

When acid is added:$$CH_3COO^-+H^+\rightarrow CH_3COOH$$CH3​COO−+H+→CH3​COOH

When base is added:$$CH_3COOH+OH^-\rightarrow CH_3COO^-+H_2O$$CH3​COOH+OH−→CH3​COO−+H2​O

Thus pH remains almost constant.

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Q19. Explain Arrhenius, Bronsted-Lowry and Lewis concepts of acids and bases.

Ans:

Arrhenius Theory:

Acid produces $H^+$H+ ions.

Base produces $OH^-$OH− ions.

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Bronsted-Lowry Theory:

Acid = proton donor

Base = proton acceptor

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Lewis Theory:

Acid = electron pair acceptor

Base = electron pair donor

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Q20. Explain solubility product with example.

Ans:

Solubility product is the equilibrium constant for a sparingly soluble salt.

Example:$$AgCl(s)\rightleftharpoons Ag^+ + Cl^-$$AgCl(s)⇌Ag++Cl− $$K_{sp}=[Ag^+][Cl^-]$$Ksp​=[Ag+][Cl−]

It indicates the solubility of ionic solids in water.

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SECTION E: Important Formula Revision

1.

$$K_c=\frac{Products}{Reactants}$$Kc​=ReactantsProducts​

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2.

$$K_p=K_c(RT)^{\Delta n}$$Kp​=Kc​(RT)Δn

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3.

$$K_w=[H^+][OH^-]$$Kw​=[H+][OH−]

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4.

$$pH=-\log[H^+]$$pH=−log[H+]

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5.

$$pH+pOH=14$$pH+pOH=14

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6.

$$K_aK_b=K_w$$Ka​Kb​=Kw​

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7.

$$pH=pK_a+\log\frac{Salt}{Acid}$$pH=pKa​+logAcidSalt​

Part 5: Full Chapter Mock Test + JEE/NEET Level Questions + Revision Sheet

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SECTION A: Full Chapter Mock Test (50 Marks)

Multiple Choice Questions (1 Mark Each)

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Q1. Chemical equilibrium is established when:

A) Concentration of reactants becomes zero
B) Forward reaction stops
C) Rate of forward reaction becomes equal to rate of reverse reaction
D) Products disappear

Ans: C) Rate of forward reaction becomes equal to rate of reverse reaction

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Q2. Which of the following is a reversible reaction?

A) Burning of coal
B) Rusting of iron
C) Formation of ammonia from nitrogen and hydrogen
D) Explosion reaction

Ans: C) Formation of ammonia from nitrogen and hydrogen

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Q3. The equilibrium constant depends on:

A) Catalyst
B) Temperature
C) Concentration
D) Pressure only

Ans: B) Temperature

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Q4. If KcK_cKc​ is greater than 1, then:

A) Reactants are favoured
B) Products are favoured
C) Reaction stops
D) No equilibrium exists

Ans: B) Products are favoured

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Q5. Which substance is not included in equilibrium constant expression?

A) Gas
B) Aqueous ions
C) Pure solid
D) Dissolved molecules

Ans: C) Pure solid

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Q6. The value of KpK_pKp​ is equal to KcK_cKc​ when:

A) Temperature is zero
B) Δn = 1
C) Δn = 0
D) Pressure is high

Ans: C) Δn = 0

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Q7. According to Le Chatelier’s principle, increasing pressure favours:

A) Side with more gas molecules
B) Side with fewer gas molecules
C) Solid formation only
D) No reaction

Ans: B) Side with fewer gas molecules

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Q8. A catalyst affects equilibrium by:

A) Changing equilibrium constant
B) Changing equilibrium position
C) Increasing rate of reaching equilibrium
D) Increasing product amount permanently

Ans: C

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Q9. The pH of a solution with hydrogen ion concentration 10−6M10^{-6}M10−6M is:

A) 4
B) 6
C) 8
D) 10

Ans: B) 6

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Q10. The ionic product of water at 25°C is:

A) $10^{-7}$10−7
B) $10^{-10}$10−10
C) $10^{-14}$10−14
D) $10^{-1}$10−1

Ans: C) 10−1410^{-14}10−14

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SECTION B: Numerical Practice Questions

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Q11. For the reaction:

$$A+B\rightleftharpoons C$$A+B⇌C

At equilibrium:$$[A]=1M,\ [B]=2M,\ [C]=4M$$[A]=1M, [B]=2M, [C]=4M

Calculate $K_c$Kc​.

Solution:$$K_c=\frac{[C]}{[A][B]}$$Kc​=[A][B][C]​ $$K_c=\frac4{1\times2}$$Kc​=1×24​ $$K_c=2$$Kc​=2

Ans: Kc=2K_c=2Kc​=2

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Q12. Calculate pH of a solution having:

$$[H^+]=1\times10^{-2}M$$[H+]=1×10−2M

Solution:$$pH=-\log(10^{-2})$$pH=−log(10−2)

Ans: pH = 2

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Q13. Calculate pOH if pH = 8.

Solution:$$pH+pOH=14$$pH+pOH=14 $$8+pOH=14$$8+pOH=14

Ans: pOH = 6

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Q14. Calculate hydroxide ion concentration if pOH = 4.

Solution:$$[OH^-]=10^{-4}$$[OH−]=10−4

Ans: 1×10−4M1\times10^{-4}M1×10−4M

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Q15. A weak acid has Ka=1×10−5K_a=1\times10^{-5}Ka​=1×10−5. Is it stronger or weaker than an acid having Ka=1×10−8K_a=1\times10^{-8}Ka​=1×10−8?

Ans: The acid with Ka=10−5K_a=10^{-5}Ka​=10−5 is stronger because higher KaK_aKa​ means greater ionisation.

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SECTION C: JEE/NEET Level Concept Questions

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Q16. For the reaction:

$$N_2+3H_2\rightleftharpoons2NH_3$$N2​+3H2​⇌2NH3​

If pressure is increased, equilibrium shifts:

A) Left
B) Right
C) No change
D) Randomly

Ans: B) Right

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Q17. For an endothermic reaction, increasing temperature will:

A) Increase products
B) Decrease products
C) Stop reaction
D) Have no effect

Ans: A

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Q18. If Q > K, the reaction will proceed:

A) Forward
B) Backward
C) Stop
D) Cannot be predicted

Ans: B) Backward

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Q19. A strong acid has:

A) Low $K_a$Ka​
B) High $K_a$Ka​
C) Low pH only
D) Zero ionisation

Ans: B) High KaK_aKa​

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Q20. Which pair forms a buffer solution?

A) HCl + NaCl
B) NaOH + KOH
C) CH₃COOH + CH₃COONa
D) HNO₃ + H₂SO₄

Ans: C

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SECTION D: Important HOTS Questions

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Q21. Why does equilibrium not mean equal concentration of reactants and products?

Ans:

Equilibrium only means equal rates of forward and reverse reactions. Concentrations depend on the value of equilibrium constant.

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Q22. Why does increasing pressure not affect the reaction:

$$H_2+I_2\rightleftharpoons2HI$$H2​+I2​⇌2HI

Ans:

Because the number of gaseous molecules is equal on both sides.

Reactants = 2 molecules

Products = 2 molecules

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Q23. Why does only temperature change equilibrium constant?

Ans:

Because equilibrium constant is a function of temperature only.

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Q24. Why are buffers important in biological systems?

Ans:

They maintain nearly constant pH required for proper functioning of biological processes.

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Q25. Why is NH3NH_3NH3​ considered a Lewis base?

Ans:

Because nitrogen in ammonia has a lone pair of electrons which it can donate.

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SECTION E: Very Important Board Questions

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Q26. Define equilibrium constant and write its expression.

Ans:

Equilibrium constant is the ratio of product concentrations to reactant concentrations at equilibrium.

For:$$aA+bB\rightleftharpoons cC+dD$$aA+bB⇌cC+dD $$K_c=\frac{[C]^c[D]^d}{[A]^a[B]^b}$$Kc​=[A]a[B]b[C]c[D]d​

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Q27. Explain the effect of concentration on equilibrium.

Ans:

Increasing reactant concentration shifts equilibrium towards products.

Increasing product concentration shifts equilibrium towards reactants.

The system opposes the change to restore equilibrium.

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Q28. Explain common ion effect with example.

Ans:

The decrease in ionisation of a weak electrolyte due to addition of a common ion is called common ion effect.

Example:$$CH_3COOH\rightleftharpoons H^++CH_3COO^-$$CH3​COOH⇌H++CH3​COO−

Addition of sodium acetate decreases ionisation of acetic acid.

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Q29. Write Henderson-Hasselbalch equation.

Ans:

For acidic buffer:$$pH=pK_a+\log\frac{Salt}{Acid}$$pH=pKa​+logAcidSalt​

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Q30. Define solubility product.

Ans:

The equilibrium constant for a sparingly soluble salt is called solubility product.

Example:$$K_{sp}=[Ag^+][Cl^-]$$Ksp​=[Ag+][Cl−]

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ONE PAGE EQUILIBRIUM REVISION SHEET

Important Concepts

Chemical Equilibrium:

• Dynamic state
• Forward rate = Reverse rate

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Equilibrium Constant:

$$K_c=\frac{Products}{Reactants}$$Kc​=ReactantsProducts​

• Large K → Products favoured
• Small K → Reactants favoured

---

Relation:

$$K_p=K_c(RT)^{\Delta n}$$Kp​=Kc​(RT)Δn

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Le Chatelier Principle:

• Concentration change → Equilibrium shifts
• Pressure change → Side with fewer gas molecules
• Temperature change → Changes K

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Ionic Equilibrium:

$$K_w=[H^+][OH^-]$$Kw​=[H+][OH−] $$K_w=10^{-14}$$Kw​=10−14

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pH:

$$pH=-\log[H^+]$$pH=−log[H+] $$pH+pOH=14$$pH+pOH=14

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Acid Strength:

$$K_a↑ \Rightarrow Acid strength↑$$Ka​↑⇒Acidstrength↑

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Base Strength:

$$K_b↑ \Rightarrow Base strength↑$$Kb​↑⇒Basestrength↑

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Buffer:

Resists change in pH.

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Solubility Product:

$$K_{sp}=[ions]^{coefficients}$$Ksp​=[ions]coefficients