MCQ Chemistry Unit 6: Equilibrium, HS 1st Year

 

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1. Which of the following is true about a system at equilibrium?
A. The rates of the forward and reverse reactions are equal.
B. The concentrations of reactants and products are equal.
C. The reaction has stopped.
D. Only the forward reaction occurs.

Answer: A

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2. What is the equilibrium constant expression for the reaction $H_2(g) + I_2(g) \leftrightarrow 2HI(g)$?
A. $K_c = \frac{[H_2][I_2]}{[HI]^2}$
B. $K_c = \frac{[HI]^2}{[H_2][I_2]}$
C. $K_c = [H_2][I_2][HI]$
D. $K_c = \frac{[HI]}{[H_2][I_2]}$

Answer: B

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3. What does Le Chatelier's principle state about a system at equilibrium when a stress is applied?
A. The system shifts to oppose the stress and restore equilibrium.
B. The system remains unaffected by the stress.
C. The forward reaction stops entirely.
D. The reverse reaction stops entirely.

Answer: A

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4. What happens to the equilibrium position when the concentration of a reactant is increased?
A. Equilibrium shifts to the right to form more products.
B. Equilibrium shifts to the left to form more reactants.
C. Equilibrium remains unchanged.
D. The system decomposes completely.

Answer: A

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5. In the equilibrium $CaCO_3(s) \leftrightarrow CaO(s) + CO_2(g)$, what happens if the pressure is increased?
A. More $CO_2$ is produced.
B. The equilibrium shifts to the left, favoring $CaCO_3$.
C. The equilibrium shifts to the right, favoring $CaO$ and $CO_2$.
D. The equilibrium remains unaffected.

Answer: B

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6. Which statement is correct regarding dynamic equilibrium?
A. No reactions occur in either direction.
B. The system must be open to the environment.
C. The concentrations of reactants and products do not change with time.
D. The forward reaction rate decreases over time while the reverse rate increases.

Answer: C

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7. According to Henry's law, the solubility of a gas in a liquid is directly proportional to:
A. Temperature of the liquid.
B. Pressure of the gas above the liquid.
C. Volume of the liquid.
D. Nature of the gas.

Answer: B

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8. For a reaction $A + B \leftrightarrow C + D$, if the equilibrium constant $K_c$ is very large, which of the following is true?
A. Reactants dominate in the equilibrium mixture.
B. Products dominate in the equilibrium mixture.
C. The reaction does not proceed significantly.
D. The reaction is at dynamic equilibrium.

Answer: B

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9. What is the equilibrium constant expression for the reaction $2SO_2(g) + O_2(g) \leftrightarrow 2SO_3(g)$?
A. $K_c = \frac{[SO_3]^2}{[SO_2]^2[O_2]}$
B. $K_c = \frac{[SO_2]^2[O_2]}{[SO_3]^2}$
C. $K_c = [SO_3]^2[SO_2]^2$
D. $K_c = [SO_3]/[SO_2][O_2]$

Answer: A

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10. Which of the following factors does NOT affect the equilibrium constant?
A. Concentration of reactants
B. Temperature
C. Nature of the reaction
D. Catalyst

Answer: D

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11. The equilibrium constant for the reaction $N_2(g) + 3H_2(g) \leftrightarrow 2NH_3(g)$ is $K_p$. What happens to $K_p$ if the reaction is reversed?
A. $K_p$ remains unchanged.
B. $K_p$ is squared.
C. $K_p$ is halved.
D. $K_p$ becomes $\frac{1}{K_p}$.

Answer: D

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12. Which of the following is true for a saturated solution of sugar in water?
A. No dynamic equilibrium exists.
B. Rate of dissolution equals rate of crystallization.
C. Only dissolution occurs.
D. Rate of crystallization is higher than the rate of dissolution.

Answer: B

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13. Which process represents a solid-vapour equilibrium?
A. Ice melting to water
B. Iodine subliming to vapour
C. Water evaporating to vapour
D. Salt dissolving in water

Answer: B

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14. The equilibrium constant $K_p$ and $K_c$ are related by the equation $K_p = K_c(RT)^{\Delta n}$. What does $\Delta n$ represent?
A. Number of moles of products
B. Number of moles of reactants
C. Change in the number of moles of gas
D. Total number of moles at equilibrium

Answer: C

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15. In a chemical equilibrium, which of the following is true for Gibbs free energy ($\Delta G$)?
A. $\Delta G > 0$
B. $\Delta G < 0$
C. $\Delta G = 0$
D. $\Delta G$ keeps changing

Answer: C

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16. According to Le Chatelier’s principle, what happens if the temperature is increased for an exothermic reaction?
A. Equilibrium shifts to the right.
B. Equilibrium shifts to the left.
C. No change in equilibrium.
D. Both directions are equally favored.

Answer: B

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17. What happens when a catalyst is added to a reaction at equilibrium?
A. Increases the equilibrium constant
B. Decreases the equilibrium constant
C. Speeds up both the forward and reverse reactions equally
D. Shifts the equilibrium position

Answer: C

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18. In the reaction $H_2(g) + I_2(g) \leftrightarrow 2HI(g)$, what happens if iodine is removed?
A. The equilibrium shifts to the left.
B. The equilibrium shifts to the right.
C. No effect on the equilibrium.
D. Reaction stops completely.

Answer: B

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19. Henry’s law relates the solubility of a gas to:
A. Its molar mass
B. The pressure of the gas
C. The temperature of the solution
D. The volume of the gas

Answer: B

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20. For the equilibrium $CO(g) + H_2O(g) \leftrightarrow CO_2(g) + H_2(g)$, the value of $K_c$ is 4.24 at 800 K. What does this imply?
A. Products are favored at equilibrium.
B. Reactants are favored at equilibrium.
C. The reaction does not proceed significantly.
D. The system is at static equilibrium.

Answer: A

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21. In a closed system at equilibrium, which of the following changes can alter the equilibrium position?
A. Addition of a catalyst
B. Change in temperature
C. Increasing the volume of the system for a gaseous reaction
D. Both B and C

Answer: D

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22. For the equilibrium $H_2O(l) \leftrightarrow H_2O(vap)$, which factor increases the equilibrium vapor pressure?
A. Adding more liquid water
B. Increasing the temperature
C. Decreasing the temperature
D. Increasing the volume of the container

Answer: B

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23. The law of chemical equilibrium states that at a given temperature:
A. All reactions proceed to completion.
B. The ratio of the product of concentrations of products to reactants raised to their stoichiometric coefficients is constant.
C. The concentration of reactants equals that of products.
D. Reactants and products have equal moles.

Answer: B

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24. For the equilibrium $2NO(g) + Cl_2(g) \leftrightarrow 2NOCl(g)$, what happens if the pressure is decreased?
A. Equilibrium shifts to the right.
B. Equilibrium shifts to the left.
C. Equilibrium is unchanged.
D. Reaction rate decreases.

Answer: B

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25. What is the effect of increasing temperature on the solubility of a gas in a liquid?
A. Solubility increases.
B. Solubility decreases.
C. Solubility remains unchanged.
D. It depends on the gas.

Answer: B

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26. In a dynamic equilibrium, the forward and reverse reactions:
A. Occur at the same rate.
B. Stop completely.
C. Are unequal in rate.
D. Favor reactants over products.

Answer: A

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27. What is the relationship between the equilibrium constant $K_c$ and the rate constants $k_f$ (forward reaction) and $k_r$ (reverse reaction)?
A. $K_c = k_f \times k_r$
B. $K_c = k_r / k_f$
C. $K_c = k_f / k_r$
D. $K_c = k_f + k_r$

Answer: C

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28. For the reaction $CaCO_3(s) \leftrightarrow CaO(s) + CO_2(g)$, what does $K_p$ represent?
A. Total pressure in the system
B. Pressure of $CO_2$ at equilibrium
C. Concentration of $CaCO_3$
D. Partial pressure of $CaO$

Answer: B

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29. In the equilibrium $H_2(g) + I_2(g) \leftrightarrow 2HI(g)$, which condition favors the formation of HI?
A. Increasing the concentration of $H_2$
B. Removing $HI$ as it forms
C. Increasing pressure
D. All of the above

Answer: D

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30. Which type of equilibrium is characterized by the coexistence of different phases?
A. Homogeneous equilibrium
B. Heterogeneous equilibrium
C. Static equilibrium
D. None of the above

Answer: B

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31. The equilibrium constant $K_c$ for the reaction $2HI \leftrightarrow H_2 + I_2$ is 0.04 at a certain temperature. What does this imply?
A. Products are favored at equilibrium.
B. Reactants are favored at equilibrium.
C. The reaction proceeds to completion.
D. Both reactants and products are present in equal amounts.

Answer: B

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32. Which of the following processes is an example of physical equilibrium?
A. Sublimation of iodine in a closed container
B. Dissolution of salt in water
C. Formation of $NH_3$ from $N_2$ and $H_2$
D. Decomposition of $CaCO_3$

Answer: A

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33. For the reaction $N_2 + 3H_2 \leftrightarrow 2NH_3$, if the temperature is increased, the equilibrium constant $K_c$:
A. Increases
B. Decreases
C. Remains constant
D. Cannot be determined

Answer: B

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34. What is the unit of $K_c$ for the reaction $2A \leftrightarrow B$?
A. No unit
B. $\text{mol/L}$
C. $(\text{mol/L})^{-1}$
D. $(\text{mol/L})^2$

Answer: C

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35. Which of the following does Henry’s law fail to apply to?
A. Oxygen in water
B. Carbon dioxide in soda
C. Hydrogen in organic solvents
D. Ammonia in water

Answer: D

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36. In a chemical equilibrium, if $Q_c < K_c$, the reaction proceeds:
A. In the forward direction
B. In the reverse direction
C. Equilibrium is already achieved
D. Reaction stops

Answer: A

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37. For the reaction $2NOCl(g) \leftrightarrow 2NO(g) + Cl_2(g)$, increasing pressure will:
A. Shift equilibrium to the right
B. Shift equilibrium to the left
C. Have no effect
D. Increase reaction rate

Answer: B

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38. At equilibrium, the concentrations of $H_2, I_2,$ and $HI$ in a reaction vessel are 0.2 M, 0.2 M, and 0.6 M, respectively. Calculate $K_c$ for the reaction $H_2 + I_2 \leftrightarrow 2HI$.
A. 9
B. 3
C. 6
D. 1

Answer: A
(Solution: $K_c = [HI]^2 / [H_2][I_2] = (0.6)^2 / (0.2)(0.2) = 9$)

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39. The addition of an inert gas to a gaseous equilibrium mixture at constant volume:
A. Shifts the equilibrium to the right
B. Shifts the equilibrium to the left
C. Has no effect on the equilibrium
D. Decreases the equilibrium constant

Answer: C

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40. The pH scale is used to measure:
A. Concentration of hydroxide ions
B. Concentration of hydrogen ions
C. Concentration of both $H^+$ and $OH^-$ ions
D. Ionic product of water

Answer: B

১. ভারসাম্য (Equilibrium) পরিচিতি

• ভারসাম্যের ধারণা পদার্থবিজ্ঞানের বিভিন্ন প্রক্রিয়া ও রাসায়নিক বিক্রিয়ায় ব্যবহৃত হয়।
• ভারসাম্য একটি গতিশীল অবস্থার পরিচায়ক, যেখানে ফরওয়ার্ড ও ব্যাকওয়ার্ড বিক্রিয়ার হার সমান।

২. পদার্থগত ভারসাম্য (Physical Equilibrium)

ক. কঠিন-তরল ভারসাম্য

• নির্দিষ্ট তাপমাত্রায় বরফ এবং পানি একটি নির্দিষ্ট স্থানে ভারসাম্য অবস্থায় থাকে।
• তাপমাত্রা ও চাপে নির্ভর করে।

খ. তরল-বাষ্প ভারসাম্য

• নির্দিষ্ট তাপমাত্রায় তরলের বাষ্প চাপ নির্দিষ্ট হয়।
• বিভিন্ন তরলের জন্য বাষ্প চাপ আলাদা হয়, যা তাদের অস্থিরতার উপর নির্ভর করে।

গ. কঠিন-বাষ্প ভারসাম্য

• কঠিন পদার্থ যেমন আয়োডিনের বাষ্পে রূপান্তর এবং পুনঃগঠনের মাধ্যমে ভারসাম্য স্থাপিত হয়।

ঘ. কঠিন বা গ্যাসের দ্রবণীয়তা

• নির্দিষ্ট তাপমাত্রায় একটি দ্রবণে দ্রাবক ও দ্রব্যের মধ্যে ভারসাম্য থাকে।
• হেনরি'স সূত্র অনুযায়ী গ্যাসের দ্রবণীয়তা চাপের সাথে আনুপাতিক।

৩. রাসায়নিক ভারসাম্য (Chemical Equilibrium)

ক. গতি এবং প্রকৃতি

• রাসায়নিক বিক্রিয়া ফরওয়ার্ড এবং ব্যাকওয়ার্ড দুটি দিকেই ঘটে।
• উদাহরণ: Haber’s প্রক্রিয়ায় অ্যামোনিয়া সংশ্লেষণ।

খ. রাসায়নিক ভারসাম্যের সূত্র

• Guldberg এবং Waage এর সূত্র অনুযায়ী, ভারসাম্য স্থিতিতে বিক্রিয়ক ও পণ্যের ঘনত্বের অনুপাত নির্দিষ্ট থাকে: $$K_c = \frac{[পণ্য]}{[বিক্রিয়ক]}$$

গ. প্রভাবিতকারী বিষয়

• তাপমাত্রা, চাপ, এবং ঘনত্ব পরিবর্তন ভারসাম্যের উপর প্রভাব ফেলে।
• Le Chatelier’s নীতিমালা এই পরিবর্তনগুলো ব্যাখ্যা করে।

৪. ব্যবহার এবং গণনা

ক. ভারসাম্যের স্থিতি নির্ণয়

• $K_c$ এর মান বড় হলে পণ্য প্রধান হয়, আর ছোট হলে বিক্রিয়ক প্রধান হয়।

খ. রাসায়নিক প্রতিক্রিয়া প্রবাহ অনুমান

• বিক্রিয়ার প্রবাহ $Q_c$ এবং $K_c$ এর তুলনা করে নির্ধারণ করা হয়।

গ. ভারসাম্যের ঘনত্ব গণনা

• প্রাথমিক ঘনত্ব থেকে ভারসাম্যের ঘনত্ব গণনা করা হয় স্টোকিওমেট্রি ব্যবহার করে।

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