IBSL Chemistry Topic 7 Equilibrium Multiple Choice Questions
Questions and Answers
- 1.
Which statement is true about chemical reactions at equilibrium?
- A.
The forward and backward reactions proceed at equal rates
- B.
The forward and backward reactions have stopped
- C.
The concentrations of the reactants and products are equal
- D.
The forward reaction is exothermic
Correct Answer
A. The forward and backward reactions proceed at equal ratesExplanation
At equilibrium, the forward and backward reactions proceed at equal rates. This means that while the reactions are still occurring, they are happening at the same rate, resulting in no net change in the concentrations of reactants and products. The equilibrium state is dynamic, with molecules constantly moving between reactants and products, but the overall concentrations remain constant.Rate this question:
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- 2.
Chemical equlibrium is referred to as dynamic because, at equilibrium, the
- A.
Equilibrium constant changes
- B.
Reactants and products keep reacting
- C.
Rates of the forward and backward reactions change
- D.
Concentrations of the reactants and products continue to change
Correct Answer
B. Reactants and products keep reactingExplanation
Chemical equilibrium is referred to as dynamic because at equilibrium, the reactants and products continue to react. Even though the concentrations of the reactants and products may appear to be constant, they are actually constantly interconverting through the forward and backward reactions. This means that while the overall concentrations may not change, the individual molecules are still undergoing reactions and interconversions. Therefore, the system is considered dynamic rather than static.Rate this question:
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- 3.
What is the equilibrium expression for the reaction:
- A.
Kc = [NH3] / ( [N2]. [H2])
- B.
Kc = 2 [NH3] / 3 ( [N2]. [H2])
- C.
Kc = 2 [NH3] / ( [N2]. [H2])
- D.
Kc = [NH3]^3 / ( [N2]. [H2]^3)
Correct Answer
D. Kc = [NH3]^3 / ( [N2]. [H2]^3)Explanation
The equilibrium expression for the reaction is Kc = [NH3]^3 / ( [N2]. [H2]^3) because it represents the ratio of the concentrations of the products (NH3) raised to their stoichiometric coefficients to the concentrations of the reactants (N2 and H2) raised to their stoichiometric coefficients. The stoichiometric coefficients in the balanced equation indicate the number of moles of each substance involved in the reaction, and raising the concentrations to these coefficients accounts for the molar ratios in the reaction.Rate this question:
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- 4.
For a reaction which goes to completion, the equilibrium constant Kc is:
- A.
>>1
- B.
- C.
=1
- D.
00
Correct Answer
A. >>1Explanation
In a reaction that goes to completion, it means that all the reactants are converted into products and no reactants are left at the end of the reaction. In such a case, the concentration of the reactants becomes zero, and the concentration of the products becomes the maximum value possible. Therefore, the equilibrium constant Kc, which is the ratio of product concentrations to reactant concentrations, will be equal to 1.Rate this question:
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- 5.
The equilibrium constant for the reaction below is 1.0 x 10^-14 at 25C and 2.1 x 10^-14 at 35C. What can be concluded from this information?
- A.
[H3O+] decreases as the temperature is raised
- B.
[H3O+] is greater than [OH-] at 35 C
- C.
Water is greater than [OH-] at 35 C
- D.
The ionization of water is endothermic
Correct Answer
D. The ionization of water is endothermicExplanation
Based on the given information, the equilibrium constant for the reaction (which represents the ionization of water) increases as the temperature is raised. This indicates that the forward reaction, which is the ionization of water into H3O+ and OH-, is favored at higher temperatures. Since the forward reaction is endothermic (absorbs heat), it can be concluded that the ionization of water is endothermic.Rate this question:
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- 6.
Ethanol is manufactured from ethene using the reaction below: Which conditions favour the highest yield of ethanol?
- A.
High pressure and low temperature
- B.
High pressure and high temperature
- C.
Low pressure and low temperature
- D.
Low pressure and high temperature
Correct Answer
A. High pressure and low temperatureExplanation
High pressure and low temperature favor the highest yield of ethanol because the reaction between ethene and water to produce ethanol is exothermic. By lowering the temperature, the reaction rate decreases, allowing more time for the reactants to convert into ethanol. Additionally, increasing the pressure increases the concentration of the reactants, which promotes the formation of more ethanol molecules. Therefore, high pressure and low temperature provide optimal conditions for maximizing the yield of ethanol.Rate this question:
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- 7.
Question No Image
- A.
I only
- B.
II only
- C.
Both I and II
- D.
Neither I nor II
Correct Answer
B. II only -
- 8.
Which change(s) will increase the amount of SO3(g) at equilibrium? I. increasing the temperature II. decreasing the temperature III. adding a catalyst
- A.
I only
- B.
II only
- C.
I and III only
- D.
I, II and III
Correct Answer
B. II onlyExplanation
Decreasing the temperature will shift the equilibrium towards the formation of more SO3(g) because it is an exothermic reaction, meaning that it releases heat. By decreasing the temperature, the reaction will favor the formation of more products to compensate for the decrease in temperature. Increasing the temperature, on the other hand, will shift the equilibrium towards the reactants, decreasing the amount of SO3(g) at equilibrium. Adding a catalyst does not affect the equilibrium position, it only speeds up the rate of the reaction.Rate this question:
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- 9.
Question No Image
- A.
High pressure and high temperature
- B.
High pressure and low temperature
- C.
Low pressure and high temperature
- D.
Low pressure and low temperature
Correct Answer
B. High pressure and low temperatureExplanation
At high pressure, the molecules are closely packed together, which reduces their kinetic energy and slows down their movement. At low temperature, the molecules have less thermal energy and move more slowly. Therefore, high pressure and low temperature conditions result in molecules being tightly packed and moving slowly.Rate this question:
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- 10.
Which statements are correct for a reaction at equilibrium? I the forward and reverse reactions both continue. II. the rates of the forward and reverse reactions are equal. III. the concentrations of reactants and products are equal.
- A.
I and II only
- B.
I and III only
- C.
II and III only
- D.
I, II and III
Correct Answer
A. I and II onlyExplanation
At equilibrium, both the forward and reverse reactions continue, which is stated in statement I. Additionally, the rates of the forward and reverse reactions are equal, as mentioned in statement II. However, statement III is incorrect because at equilibrium, the concentrations of reactants and products are not necessarily equal, but rather they reach a state of dynamic balance.Rate this question:
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- 11.
Which statement is always true for a chemical reaction that has reached equilibrium?
- A.
The yield of product(s) is greater than 50%
- B.
The rate of the forward reaction is greater than the rate of the reverse reaction
- C.
The amounts of reactants and products do not change
- D.
Both forward and reverse reactions have stopped
Correct Answer
C. The amounts of reactants and products do not changeExplanation
In a chemical reaction that has reached equilibrium, the amounts of reactants and products do not change. This means that the rate of the forward reaction is equal to the rate of the reverse reaction, resulting in a constant concentration of reactants and products. At equilibrium, the reaction is still occurring, but there is no net change in the amounts of reactants and products over time.Rate this question:
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- 12.
The manufacture of sulfur trioxide can be represented by the equation below: What happens when a catalyst is added to an equilibrium mixture from this reaction?
- A.
The rate of the forward reaction increases and that of the reverse reaction decreases
- B.
The rates of both forward and reverse reactions increase
- C.
The value of enthalpy difference increases
- D.
The yield of sulfur trioxide increases
Correct Answer
B. The rates of both forward and reverse reactions increaseExplanation
When a catalyst is added to an equilibrium mixture from this reaction, it provides an alternative pathway with lower activation energy for both the forward and reverse reactions. This means that more reactant molecules can successfully collide and react, increasing the rate of both reactions. As a result, the rates of both the forward and reverse reactions increase simultaneously. The addition of a catalyst does not affect the enthalpy difference or the yield of sulfur trioxide.Rate this question:
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- 13.
What will happen to the position of equilibrium and the value of the equilibrium constant when the temperature is increased in the following reaction?
- A.
The position of equilibrium shifts towards the reactants and the value of the equilibrium constant decreases
- B.
The position of equilibrium shifts towards the reactants and the value of the equilibrium constant increases
- C.
The position of equilibrium shifts towards the products and the value of the equilibrium constant decreases
- D.
The position of equilibrium shifts towards the products and the value of the equilibrium constant increases
Correct Answer
D. The position of equilibrium shifts towards the products and the value of the equilibrium constant increasesExplanation
When the temperature is increased in a reaction, it generally favors the endothermic direction. This means that the position of equilibrium shifts towards the products. Additionally, an increase in temperature usually leads to a decrease in the value of the equilibrium constant. Therefore, the given answer is correct.Rate this question:
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- 14.
Which change will shift the position of equilibrium to the right in the following reaction? I. adding a catalyst II. decreasing the oxygen concentration III. increasing the volume of the container
- A.
I and II only
- B.
I and III only
- C.
II and III only
- D.
I, II and III
Correct Answer
C. II and III onlyExplanation
Decreasing the oxygen concentration will shift the position of equilibrium to the right because oxygen is a reactant in the reaction. By decreasing its concentration, the reaction will favor the forward reaction to produce more products. Increasing the volume of the container will also shift the equilibrium to the right because it will decrease the pressure. According to Le Chatelier's principle, the reaction will shift in the direction that reduces the pressure, favoring the side with more moles of gas, which in this case is the side with more products. Adding a catalyst will not shift the position of equilibrium as it only speeds up the rate of the reaction.Rate this question:
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- 15.
Which statement(s) is/are true for a mixture ofice and water at equilibrium? I. the rates of melting and freezing are equal II. the amounts of ice and water are equal III. the same position of equilibrium can be reached by cooling water and heating ice
- A.
I only
- B.
I and III only
- C.
II only
- D.
III only
Correct Answer
B. I and III onlyExplanation
The statement I is true because at equilibrium, the rates of melting and freezing are equal. This means that the amount of ice that melts is equal to the amount of water that freezes.
The statement III is also true because the same position of equilibrium can be reached by cooling water and heating ice. When water is cooled, it will freeze and reach equilibrium with the ice. Similarly, when ice is heated, it will melt and reach equilibrium with the water. Therefore, the same position of equilibrium can be achieved by both cooling water and heating ice.Rate this question:
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- 16.
In the Haber process for the synthesis of ammonia, what effects does the catalyst have?
- A.
Increases the rate of formation of ammonia and increases the amount of ammonia formed
- B.
Increases the rate of formation of ammonia and decreases the amount of ammonia formed
- C.
Increases the rate of formation of ammonia and does not change the amount of ammonia formed
- D.
Does not change the rate of formation of ammonia and increases the amount of ammonia formed
Correct Answer
C. Increases the rate of formation of ammonia and does not change the amount of ammonia formedExplanation
The catalyst in the Haber process for the synthesis of ammonia increases the rate of formation of ammonia by providing an alternative pathway for the reaction to occur. It does not change the amount of ammonia formed because it does not affect the equilibrium position of the reaction. The catalyst speeds up the forward and backward reactions equally, resulting in an increased rate of formation without changing the overall amount of ammonia produced.Rate this question:
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- 17.
According to the above information what temperature and pressure conditions produce the greatest amount of SO3?
- A.
Low Temperature and low Pressure
- B.
Low Temperature and high Pressure
- C.
High Temperature and high Pressure
- D.
High Temperature and low Pressure
Correct Answer
B. Low Temperature and high PressureExplanation
Low temperature and high pressure conditions produce the greatest amount of SO3. This is because the reaction to produce SO3 is exothermic, meaning it releases heat. By keeping the temperature low, the reaction is not favored and less SO3 is produced. However, by increasing the pressure, the equilibrium of the reaction is shifted towards the formation of more SO3, resulting in a greater yield.Rate this question:
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- 18.
Chemical equilibrium is referred to as dynamic because, at equilibrium, the
- A.
Equilibrium constant changes.
- B.
Reactants and products keep reacting.
- C.
Rates of the forward and backward reactions change.
- D.
Concentrations of the reactants and products continue to change.
Correct Answer
B. Reactants and products keep reacting.Explanation
At chemical equilibrium, the reaction does not stop. Instead, the forward and backward reactions continue to occur at equal rates. This means that the reactants are still being converted into products, and the products are still being converted back into reactants. However, the concentrations of the reactants and products no longer change because the rates of the forward and backward reactions are equal, resulting in a constant concentration of each species. Therefore, the correct answer is that reactants and products keep reacting.Rate this question:
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- 19.
Which change will shift the position of equilibrium to the right in this reaction? N2(g) +3H2 (g) <-> 2NH3 (g) ∆H =−92 kJ/mol
- A.
Increasing the temperature
- B.
Adding a catalyst
- C.
Decreasing the pressure
- D.
Removing ammonia from the equilibrium mixture
Correct Answer
D. Removing ammonia from the equilibrium mixtureExplanation
Removing ammonia from the equilibrium mixture will shift the position of equilibrium to the right because according to Le Chatelier's principle, when a product is removed from the reaction mixture, the equilibrium will shift in the direction that produces more of that product. In this case, removing ammonia will cause the reaction to produce more ammonia in order to replace the ammonia that was removed, thus shifting the equilibrium to the right.Rate this question:
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- 20.
Which of the following changes will shift the position of equilibrium of this reaction in the forward direction? N2(g) + O2 (g) ↔ 2 NO(g) ∆H = +181 kJ/mol I. Increasing the pressure II. Adding a catalyst III. Increasing the temperature
- A.
I only
- B.
II only
- C.
III only
- D.
I and III
Correct Answer
C. III onlyExplanation
Increasing the temperature will shift the position of equilibrium of the reaction in the forward direction. This is because the reaction is endothermic (∆H = +181 kJ/mol), meaning it absorbs heat. According to Le Chatelier's principle, increasing the temperature will favor the endothermic reaction. This shift in equilibrium will result in more products being formed, which in this case is NO(g). Therefore, only increasing the temperature will shift the equilibrium in the forward direction.Rate this question:
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- 21.
For a gaseous reaction, the equilibrium constant expression is: Kc = [O2]5[NH3]4 [NO]4[H2O]6 Which equation corresponds to this equilibrium expression?
- A.
4NH3 + 5O2 ↔ 4NO + 6H2O
- B.
8NH3 +10 O2 ↔ 8NO +12H2O
- C.
4NO + 6H2O ↔ 4NH3 + 5O2
- D.
2NO + 3H2O ↔ 2NH3 + 5/2 O2
Correct Answer
C. 4NO + 6H2O ↔ 4NH3 + 5O2Explanation
The equation 4NO + 6H2O ↔ 4NH3 + 5O2 corresponds to the given equilibrium constant expression, Kc = [O2]5[NH3]4 / [NO]4[H2O]6. This equation shows the stoichiometric relationship between the reactants (4NO and 6H2O) and the products (4NH3 and 5O2) in the gaseous reaction.Rate this question:
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- 22.
Which statement(s) is/are true for a mixture of ice and water at equilibrium? I. The rates of melting and freezing are equal. II. The amounts of ice and water are equal. III. The same position of equilibrium can be reached by cooling water and heating ice.
- A.
I only
- B.
I and III only
- C.
II only
- D.
III only
Correct Answer
B. I and III onlyExplanation
In a mixture of ice and water at equilibrium, statement I is true because the rates of melting and freezing are equal. This means that the amount of ice melting is equal to the amount of water freezing. Statement III is also true because the same position of equilibrium can be reached by cooling water and heating ice. This means that by cooling the water, some of it will freeze into ice, and by heating the ice, some of it will melt into water, eventually reaching the same equilibrium position. Statement II is not true because the amounts of ice and water can vary at equilibrium depending on the temperature and pressure conditions.Rate this question:
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- 23.
Which statement concerning a chemical reaction at equilibrium is not correct?
- A.
The concentrations of reactants and products remain constant.
- B.
Equilibrium can be approached from both directions.
- C.
The rate of the forward reaction equals the rate of the reverse reaction.
- D.
All reaction stops.
Correct Answer
D. All reaction stops.Explanation
The statement "All reaction stops" is not correct. In a chemical reaction at equilibrium, the forward and reverse reactions continue to occur at equal rates, resulting in a dynamic equilibrium where the concentrations of reactants and products remain constant. While the overall concentrations do not change, the individual molecules are constantly reacting and interconverting.Rate this question:
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