Chemical Equilibrium Test 2

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Question 1:

In an exothermic and reversible process of ammonia creation, what would be the outcome if it's cooled?

A) Increased formation of N₂
B) Increased formation of H₂
C) Increased production of ammonia
D) More reactant will form

Topic: Exothermic Reactions and Reaction Rates

Correct Answer: C) Increased production of ammonia

Detailed Hint:

In reversible reactions, the reaction can proceed in both forward (product formation) and backward (reactant formation) directions.
Exothermic reactions release heat, hence, a decrease in temperature (cooling) will favor the forward direction to compensate for the lost heat.
Therefore, cooling an exothermic process like the formation of ammonia leads to an increase in product (ammonia) formation.
Thus, the correct answer is C, "Increased production of ammonia".

Question 2:

Given the reaction equilibrium N₂O_4(g) ⇌ 2NO_2(g), with N₂O₄ and NO₂ concentrations at equilibrium being 4.8×10^-2 and 1.2×10^-2 mol/L respectively, what is the value of the reaction's K_c?

A) 0.25×10^-2 mol/L
B) 0.3×10^-3 mol/L
C) 3×10^-3 mol/L
D) 4.8×10^-2 mol/L

Topic: Reaction Equilibrium and Equilibrium Constant

Correct Answer: C) 3×10^-3 mol/L

Detailed Explanation:

The reaction's equilibrium constant, K_c, is calculated as K_c = [NO₂]²/[N₂O₄].
Substituting the given values, we get K_c = (1.2×10^-2)²/4.8×10^-2 = 0.3×10^-2 or 3.0×10^-3 mol/L.
Thus, the correct answer is C, "3×10^-3 mol/L".

Question 3:

Identify the factor which has no influence on the reversible reaction 2HI → H₂ + I₂.

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

Topic: Factors Influencing Reversible Reactions

Correct Answer: D) Pressure

Detailed Explanation:

In this reversible reaction, the number of moles of reactants is equal to the number of moles of products.
Therefore, the pressure does not affect the equilibrium of the reaction.
Volume changes, however, will influence the equilibrium, for instance, increasing the H₂ volume will shift the equilibrium towards the reactants.
Both temperature and catalysts also affect the equilibrium.
Thus, the correct answer is D, "Pressure".

Question 4:

Which of the following can perturb a system at equilibrium?

A) Concentration change
B) Pressure change
C) Temperature
D) All of the above

Topic: Disturbances in Equilibrium Systems

Correct Answer: D) All of the above

Detailed Explanation:

According to Le Chatelier’s principle, any system at equilibrium will adjust to counteract any changes in concentration, temperature, volume, or pressure, thus establishing a new equilibrium.
Therefore, all the options provided can disrupt a system at equilibrium.
Thus, the correct answer is D, "All of the above".

Question 5:

Given that 1 mol/L of A₂ is a reactant and 11% of it dissociates into B and C at equilibrium according to the reaction A₂ ⇌ B + C, what is the K_c of the reaction?

A) 1.2
B) 1.36
C) 1.48
D) 2.36

Topic: Equilibrium Constant for Dissociation Reactions

Correct Answer: B) 1.36

Detailed Explanation:

11% of A₂ gets dissociated which means 11 out of 100 parts of A₂ convert into B and C.
Therefore, the correct answer is B, "1.36".

Question 6:

Considering the reaction A → B + C, if K_p = 1.2 at 1000 K, what is the value of K_c for this reaction?

A) 0.010
B) 0.015
C) 0.025
D) 0.038

Topic: Equilibrium Constants at Given Temperatures

Correct Answer: B) 0.015

Detailed Explanation:

K_p and K_c are related by the equation K_p = K_c(RT)^Δn, where Δn = 1 for this reaction.
Substituting the known values, we get 1.2 = K_c (0.08 x 1000), which simplifies to K_c = 0.015.
Thus, the correct answer is B, "0.015".

Question 7:

For the equilibrium reaction A + B ⇌ C + D, if some of C is removed from the system at equilibrium, what would be the reaction's response?

A) Remain at equilibrium
B) Proceed in the forward direction
C) Proceed in the reverse direction
D) Continue without ever reaching equilibrium

Topic: Reaction Direction upon Component Removal

Correct Answer: B) Proceed in the forward direction

Detailed Explanation:

According to Le Chatelier’s principle, when a system at equilibrium is disturbed, it will adjust to nullify the effect of the disturbance.
In this case, the removal of C will prompt the reaction to shift in the forward direction to replace the lost C.
Thus, the correct answer is B, "Proceed in the forward direction".

Question 8:

In the reaction H2 + I2 → 2HI, what are the units of Kc?

A) mol²dm^-6
B) mol dm^-3
C) No unit
D) mol^-2dm⁶

Topic: Determination of Equilibrium Constant Units

Correct Answer: C) No unit

Hint:

The equilibrium constant Kc is determined by the ratio of the concentrations of the products to the reactants, each raised to the power of their stoichiometric coefficients.
In this reaction, Kc = [HI]^2 / ([H2] [I2]).
Considering the units, we get [moldm^-3]^2 / ([moldm^-3] [moldm^-3]), which simplifies to no units.
Thus, the correct answer is C, "No unit".

Question 9:

In the reaction H2 + I2 → 2HI, what are the units of the equilibrium constant, Kc?

A) mol²dm^-6
B) mol dm^-3
C) No unit
D) mol^-2dm⁶

Topic: Calculation of Equilibrium Constant Units

Correct Answer: C) No unit

Hint:

The units of the equilibrium constant Kc are derived from the equation Kc = [products] / [reactants], where the concentrations are raised to their respective stoichiometric coefficients.
For this reaction, Kc = [HI]^2 / ([H2] [I2]).
This yields units of [moldm^-3]^2 / ([moldm^-3] [moldm^-3]), which simplifies to no units.
Thus, the correct answer is C, "No unit".

Question 10:

According to Le Chatelier's Principle, which of the following statements is true?

A) If a stress is applied to a system before it reaches equilibrium, the system acts to nullify the effect of stress.
B) If a stress is applied to a system before it reaches equilibrium, the system acts to support the effect of stress.
C) If a stress is applied to a system at equilibrium, the system acts to support the effect of stress.
D) If a stress is applied to a system at equilibrium, the system acts to nullify the effect of stress.

Topic: Understanding Le Chatelier's Principle

Correct Answer: D) If a stress is applied to a system at equilibrium, the system acts to nullify the effect of stress.

Hint:

According to Le Chatelier’s Principle, when a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the reactants or products, the system will shift its equilibrium position so as to counteract the effect of the disturbance.
Therefore, if a stress is applied to a system at equilibrium, the system will adjust in such a way as to minimize the stress.
Thus, the correct answer is D, "If a stress is applied to a system at equilibrium, the system acts to nullify the effect of stress".

Question 11:

What is it called when the ionization of a weak electrolyte is suppressed by adding a common ion from an external source?

A) Common electrolyte effect.
B) Ionization effect.
C) Common ion effect.
D) Le-Chatelier's principle.

Topic: Ion Suppression and the Common Ion Effect

Correct Answer: C) Common ion effect

Hint:

When a weak electrolyte is present in a solution, it ionizes to a small extent.
If an ion common to the electrolyte is added from an external source, the ionization of the weak electrolyte is further suppressed.
This is known as the Common Ion Effect.
Thus, the correct answer is C, "Common ion effect".

Question 12:

What are the optimum conditions for the Haber process?

A) High temperature and high pressure.
B) Low temperature and low pressure.
C) High temperature and low pressure.
D) Low temperature and high pressure.

Topic: Conditions for the Haber Process

Correct Answer: D) Low temperature and high pressure.

Hint:

The Haber process is a method for synthesizing ammonia from nitrogen and hydrogen.
It is an exothermic reaction, hence a lower temperature would favor the production of ammonia.
However, the reaction involves a reduction in volume, therefore high pressure also favors the production of ammonia.
Thus, the correct answer is D, "Low temperature and high pressure".

Question 13:

In the equilibrium PCl5 ⇌ PCl3 + Cl2; ΔH = 22 kcal, the disintegration of PCl5 will be more on?

A) Increasing pressure.
B) Increasing concentration of chlorine.
C) Increasing temperature.
D) Decreasing temperature.

Topic: Le Chatelier's Principle and the Effect of Temperature Changes

Correct Answer: C) Increasing temperature.

Hint:

In an endothermic reaction like PCl5 ⇌ PCl3 + Cl2 (ΔH = 22 kcal), heat is absorbed.
According to Le Chatelier's Principle, increasing the temperature will drive the reaction to the right, causing more disintegration of PCl5.
Also, as there are more moles of gas on the right side of the equation, decreasing the pressure would favor the disintegration.
Thus, the correct answer is C, "Increasing temperature".

Question 14:

To which types of systems does Le-Chatelier’s principle apply?

A) Mechanical systems.
B) Physical systems.
C) Chemical systems.
D) Both B and C.

Topic: Understanding Le-Chatelier’s Principle

Correct Answer: D) Both B and C.

Hint:

Le Chatelier's Principle is an important concept in the field of chemistry and physics that explains the behavior of systems in equilibrium when subjected to changes in conditions.
It applies to both physical and chemical systems undergoing changes in temperature, pressure, volume, or concentration. The system will adjust itself in a way to minimize the stress and achieve a new state of equilibrium.
Therefore, the correct answer is D, "Both Physical and Chemical systems".

Question 15:

Which condition favors endothermic reactions in the forward direction?

A) Cooling.
B) Freezing.
C) Heating.
D) Adding a catalyst.

Topic: Conditions Favoring Endothermic Reactions

Correct Answer: C) Heating.

Short Hint:

Endothermic reactions absorb heat, so they are favored by an increase in temperature.
Cooling or freezing would not favor endothermic reactions, and adding a catalyst does not necessarily favor the forward direction.
Therefore, the correct answer is C, "Heating".

Question 16:

How are the equilibrium constants expressed in terms of concentration (Kc) and partial pressures (Kp) related in the reaction H2(g) + I2(g) ⇌ 2HI(g)?

A) Kp = Kc(RT)^2.
B) Kc = Kp(RT)^2.
C) Kp = Kc.
D) Kp = Kc(RT)^3.

Topic: Interrelationship between Kp and Kc

Correct Answer: C) Kp = Kc.

Short Hint:

Kp and Kc are related by the equation Kp = Kc(RT)^Δn, where Δn is the change in moles of gas.
In the given reaction, Δn = 0, so Kp = Kc.

Question 17:

In the given reaction PCl5(g) ⇌ PCl3(g) + Cl2(g), the equilibrium concentrations of PCl5 and PCl3 are 0.4 and 0.2 mole/litre respectively. If the KC value is 0.5, what is the concentration of Cl2 in mole/litre?

A) 0.5.
B) 1.0.
C) 1.5.
D) 2.0.

Topic: Calculating Equilibrium Concentrations

Correct Answer: B) 1.0.

Short Hint:

Use the equilibrium constant expression KC = [PCl3][Cl2] / [PCl5] to calculate [Cl2].
Substitute the given values to find [Cl2] = 1 mole/litre.

Question 18:

Which of the following aqueous solutions would produce an Acidic buffer solution?

A) NH4Cl + NH4OH.
B) CH3COONa + CH3COOH.
C) NaCl + NaOH.
D) Na2SO4 + H4SO4.

Topic: Formulating Acidic Buffer Solutions

Correct Answer: B) CH3COONa + CH3COOH.

Short Hint:

An acidic buffer is created using a weak acid and its salt, which comes from a strong base.
Option B, CH3COONa + CH3COOH, is a mixture of acetic acid (a weak acid) and sodium acetate (its salt with strong base sodium hydroxide) and will create an acidic buffer.

Question 19:

Given the system A + B ⇋ C + D, how much of the reaction is complete when Kc = 1?

A) 10%.
B) 25%.
C) 50%.
D) 100%.

Topic: Reactivity and Equilibrium Constants

Correct Answer: C) 50%.

Short Hint:

When Kc = 1, it implies that the concentrations of the reactants and the products are the same.
Therefore, it can be inferred that 50% of the reaction is complete.

Question 20:

What is the impact of dilution on the acid dissociation constant (Ka) under a constant temperature regime?

A) Ka increases.
B) Ka decreases.
C) Ka remains unchanged.
D) Ka sharply decreases.

Topic: Acid Dilution and its Impact on Ka

Correct Answer: C) Ka remains unchanged.

Short Hint:

Ka is a fixed value for a particular acid at a specific temperature and doesn't depend on the concentration or dilution of the acid.
Therefore, Ka remains the same under a constant temperature regime, regardless of dilution.

Question 21:

For the reaction N2(g) + 3H2(g) ⇋ 2NH3(g) with an enthalpy change ∆H = 92.46 Kj/mol, what would be the optimal temperature for ammonia production?

A) 5000°C.
B) 450°C.
C) 0°C.
D) Temperature remains constant.

Topic: Optimal Conditions for Ammonia Production

Correct Answer: B) 450°C.

Short Hint:

The production of ammonia is an exothermic reaction, and the ideal temperature for ammonia production is around 450 - 500°C, under high pressure and in the presence of a catalyst.

MCQs 22:

A buffer solution is known to resist or minimize changes in which parameter?

A) pH.
B) pOH.
C) PKa.
D) PKb.

Topic: Characteristics of Buffer Solutions

Correct Answer: A) pH.

Hint:

A buffer solution is designed to maintain a constant pH.
It achieves this by resisting changes in the pH value.
So, the main parameter that a buffer solution minimizes changes in is pH.

MCQs 23:

In which of the following reactions is the equilibrium state not influenced by volume adjustments?

A) 2SO2 + O2 ⇌ 2SO2.
B) PCl5 ⇌ PCl3 + Cl2.
C) N2 + 3H2 ⇌ 2NH3.
D) 2HF ⇌ H2 + F2.

Topic: Influences on Gaseous Reaction Equilibria

Correct Answer: D) 2HF ⇌ H2 + F2.

Hint:

The equilibrium state is not influenced by volume adjustments when the number of moles of reactants equals the number of moles of products.
In the given options, only the reaction 2HF ⇌ H2 + F2 satisfies this condition.

MCQs 24:

What does a small value of Kc signify in a reaction at equilibrium?

A) The reaction has an equal amount of products and reactants at equilibrium.
B) The equilibrium favors the forward direction.
C) The equilibrium is less favored towards the forward direction.
D) The reversible reaction would never reach equilibrium.

Topic: Significance of Kc Values in Reaction Equilibria

Correct Answer: C) The equilibrium is less favored towards the forward direction.

Hint:

A small value of Kc indicates a larger concentration of reactants compared to products at equilibrium.
This means that the equilibrium is less favored towards the forward direction.

MCQs 25:

If 2 moles of PCl5 are heated to 400°C in a closed 2-liter vessel and 40% of the PCl5 dissociates into PCl3 and Cl2 at equilibrium, what would be the value of its Kc?

A) 0.267 mol/liter.
B) 0.548 mol/liter.
C) 2.342 mol/liter.
D) None of the above.

Topic: Calculation of Kc Values

Correct Answer: A) 0.267 mol/liter.

Hint:

Calculate the concentrations of the components at equilibrium based on the given information.
Use these concentrations to calculate the value of Kc for the reaction.

MCQs 26:

When does a forward reaction practically proceed to completion based on the value of Kc?

A) When Kc is small and positive.
B) When Kc is large and positive.
C) When Kc is large and negative.
D) When Kc is equal to one.

Topic: Role of Kc in Determining the Direction of Reaction

Correct Answer: B) When Kc is large and positive.

Hint:

A large and positive value of Kc indicates that the forward reaction is highly favored.
Practically, the forward reaction proceeds to completion in such cases.

MCQs 27:

When would the value of Kp be greater than Kc given the difference in moles of the products and reactants?

A) When the difference is zero.
B) When the difference is positive.
C) When the difference is negative.
D) When the difference is one.

Topic: Comparative Analysis between Kp and Kc

Correct Answer: B) When the difference is positive.

Hint:

The relationship between Kp and Kc is influenced by the change in the number of moles of gas molecules (Δn).
If Δn is positive (more moles of gas products than reactants), Kp is greater than Kc.

MCQs 28:

Why would AgCl get precipitated out when some NaCl salt is added to its solution?

A) Due to solubility.
B) Due to being an electrolyte.
C) Due to unsaturation.
D) Due to the common ion effect.

Topic: Impact of the Common Ion Effect on Precipitation

Correct Answer: D) Due to the common ion effect.

Hint:

The common ion effect reduces the solubility of a salt when a common ion is added to the solution.
When NaCl is added to an AgCl solution, the common ion Cl- reduces the solubility of AgCl, leading to precipitation.

Chemical Equilibrium Test 2

Question 1:

Topic: Exothermic Reactions and Reaction Rates

Question 2:

Topic: Reaction Equilibrium and Equilibrium Constant

Question 3:

Topic: Factors Influencing Reversible Reactions

Question 4:

Topic: Disturbances in Equilibrium Systems

Question 5:

Topic: Equilibrium Constant for Dissociation Reactions

Question 6:

Topic: Equilibrium Constants at Given Temperatures

Question 7:

Topic: Reaction Direction upon Component Removal

Question 8:

Topic: Determination of Equilibrium Constant Units

Question 9:

Topic: Calculation of Equilibrium Constant Units

Question 10:

Topic: Understanding Le Chatelier's Principle

Question 11:

Topic: Ion Suppression and the Common Ion Effect

Question 12:

Topic: Conditions for the Haber Process

Question 13:

Topic: Le Chatelier's Principle and the Effect of Temperature Changes

Question 14:

Topic: Understanding Le-Chatelier’s Principle

Question 15:

Topic: Conditions Favoring Endothermic Reactions

Question 16:

Topic: Interrelationship between Kp and Kc

Question 17:

Topic: Calculating Equilibrium Concentrations

Question 18:

Topic: Formulating Acidic Buffer Solutions

Question 19:

Topic: Reactivity and Equilibrium Constants

Question 20:

Topic: Acid Dilution and its Impact on Ka

Question 21:

Topic: Optimal Conditions for Ammonia Production

MCQs 22:

Topic: Characteristics of Buffer Solutions

MCQs 23:

Topic: Influences on Gaseous Reaction Equilibria

MCQs 24:

Topic: Significance of Kc Values in Reaction Equilibria

MCQs 25:

Topic: Calculation of Kc Values

MCQs 26:

Topic: Role of Kc in Determining the Direction of Reaction

MCQs 27:

Topic: Comparative Analysis between Kp and Kc

MCQs 28:

Topic: Impact of the Common Ion Effect on Precipitation

Test Results