Which one of the following statements is false about dynamic equilibrium?
Solution:
Dynamic equilibrium can indeed be disturbed by external stresses such as changes in concentration, pressure, or temperature, which is described by Le Chatelier's Principle.
Which of the following best represents the equilibrium constant expression (\(K_c\)) for the reaction: \(4\text{NH}_3(g) + 5\text{O}_2(g) \rightleftharpoons 4\text{NO}(g) + 6\text{H}_2\text{O}(g)\)?
Solution:
The equilibrium constant expression is given by the ratio of the concentrations of the products to the reactants, each raised to the power of their stoichiometric coefficients.
A reaction which never goes to completion is known as reversible reaction. Reversible reaction is represented by:
Solution:
A reversible reaction is represented by a double arrow, indicating that the reaction can proceed in both the forward and reverse directions.
When the magnitude of \(K_c\) is small, it indicates:
Solution:
A small \(K_c\) value indicates that the equilibrium mixture contains mostly reactants, suggesting that the forward reaction does not proceed very far.
For which system does the equilibrium constant, \(K_c\), have units of concentration?
Solution:
When the number of moles of gaseous products and reactants are different, \(K_c\) has units of concentration. In this case, the presence of a liquid (\(\text{H}_2\text{O}(l)\)) means it is not included in the equilibrium expression, leading to units for \(K_c\).
The unit of \(K_c\) for the reaction \(\text{N}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{NO}(g)\) is:
Solution:
For this reaction, the number of moles of gaseous reactants and products are equal, so \(K_c\) has no units.
The system is stable in equilibrium when:
Solution:
The system is at equilibrium and stable when the reaction quotient \(Q_c\) equals the equilibrium constant \(K_c\).
\(Q_c\) can be defined as:
Solution:
The reaction quotient \(Q_c\) is defined as the ratio of the molar concentrations of products to reactants, each raised to the power of their stoichiometric coefficients, at any point in time.
The value of \(K_c\) increases when:
Solution:
The equilibrium constant \(K_c\) increases when the concentration of products increases, indicating a shift towards the product side.
What characterizes a chemical equilibrium in a reversible reaction?
Solution:
At chemical equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. This means that the concentrations of reactants and products remain constant over time.
What is the significance of the equilibrium constant (\(K_c\))?
Solution:
The equilibrium constant \(K_c\) provides information about the extent of the reaction and the direction in which the reaction will proceed to reach equilibrium.
Which statement is true about reversible reactions?
Solution:
Reversible reactions can proceed in both the forward and backward directions, and they do not necessarily go to completion.
What does the Law of Mass Action state?
Solution:
The Law of Mass Action states that the rate of a reaction is directly proportional to the product of the concentrations (active masses) of the reactants.
Which of the following affects the value of equilibrium constant \(K_c\)?
Solution:
The value of the equilibrium constant \(K_c\) is affected by temperature. Changes in temperature can shift the equilibrium position, altering the value of \(K_c\).
What is true about the reaction quotient \(Q_c\) under non-equilibrium conditions?
Solution:
The reaction quotient \(Q_c\) is defined as the ratio of the concentrations of products to reactants at any point in the reaction, not just at equilibrium.
Which condition is required for a dynamic equilibrium to be established?
Solution:
Dynamic equilibrium can only be established in a closed system where no substances can enter or leave, allowing the forward and reverse reactions to proceed at equal rates.
In the Haber process, which of the following represents the forward reaction?
Solution:
In the Haber process, the forward reaction is the synthesis of ammonia from nitrogen and hydrogen gases: \(\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3\).
What happens to the rate of the forward reaction as the concentration of reactants decreases?
Solution:
As the concentration of reactants decreases, the rate of the forward reaction decreases because there are fewer reactant molecules available to collide and react.
Which of the following is NOT a macroscopic characteristic of dynamic equilibrium?
Solution:
At dynamic equilibrium, the concentrations of reactants and products remain constant over time, even though the forward and reverse reactions continue to occur.
According to the Law of Mass Action, the rate of a chemical reaction is directly proportional to:
Solution:
The Law of Mass Action states that the rate of a chemical reaction is directly proportional to the product of the concentrations (active masses) of the reactants.
In the reaction: \(aA + bB \rightleftharpoons cC + dD\), the equilibrium constant (\(K_c\)) expression is:
Solution:
The equilibrium constant expression for a reaction is given by the ratio of the product of the concentrations of the products to the product of the concentrations of the reactants, each raised to the power of their stoichiometric coefficients.
What happens to the rate of forward and reverse reactions at equilibrium?
Solution:
At equilibrium, the rates of the forward and reverse reactions are equal, which means that the concentrations of reactants and products remain constant.
What is meant by 'active mass'?
Solution:
'Active mass' refers to the concentration of a reacting substance, typically expressed in moles per liter.
For the reaction \(2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)\), the correct equilibrium constant expression is:
Solution:
The equilibrium constant expression for this reaction is the ratio of the concentration of the product \(\text{SO}_3\) squared to the product of the concentrations of the reactants \(\text{SO}_2\) squared and \(\text{O}_2\).
What is the unit of active mass?
Solution:
The unit of active mass, which refers to the concentration of a substance in a reaction, is typically expressed as moles per cubic decimeter (\(\text{mol/dm}^3\)).
Which of the following affects the value of the equilibrium constant (\(K_c\))?
Solution:
The value of the equilibrium constant \(K_c\) is affected by temperature. Changes in temperature can shift the equilibrium position, altering the value of \(K_c\).
What does it indicate if the value of \(K_c\) is greater than 1?
Solution:
If the value of \(K_c\) is greater than 1, it indicates that the reaction favors the formation of products, meaning the forward reaction is predominant at equilibrium.
What is the unit of \(K_c\) when the number of moles of reactants equals the number of moles of products?
Solution:
When the number of moles of reactants equals the number of moles of products, the units for \(K_c\) cancel out, resulting in a dimensionless quantity with no units.
Which of the following is not a correct characteristic of the equilibrium constant (\(K_c\))?
Solution:
The equilibrium constant \(K_c\) does not change with changing concentrations of reactants or products. It remains constant at a given temperature.
In the reaction: \(\text{CO}_2(g) + \text{H}_2(g) \rightleftharpoons \text{CO}(g) + \text{H}_2\text{O}(l)\), what is the unit of \(K_c\)?
Solution:
In this reaction, since one of the products is a liquid (\(\text{H}_2\text{O}(l)\)) and does not appear in the equilibrium expression, the units for \(K_c\) cancel out, resulting in no units.
What does the value of the equilibrium constant (\(K_c\)) help determine in a chemical reaction?
Solution:
The equilibrium constant \(K_c\) helps determine the direction in which a reaction will proceed to reach equilibrium and the extent to which the reaction will form products.
Which of the following statements is TRUE when \(Q_c < K_c\)?
Solution:
When \(Q_c < K_c\), the reaction will proceed in the forward direction to produce more products until equilibrium is reached.
What happens in a chemical reaction when \(Q_c > K_c\)?
Solution:
When \(Q_c > K_c\), the reverse reaction will occur, converting products back into reactants until the system reaches equilibrium.
What is the condition of the reaction when \(Q_c = K_c\)?
Solution:
When \(Q_c = K_c\), the system is at equilibrium, meaning the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.
What does a very small \(K_c\) value indicate about the reaction?
Solution:
A very small \(K_c\) value indicates that the reaction strongly favors the reactants and does not proceed significantly towards product formation.
What does a very large \(K_c\) value tell us about a reaction?
Solution:
A very large \(K_c\) value indicates that the reaction strongly favors the products and proceeds almost to completion.
A reaction with a moderate \(K_c\) value indicates that:
Solution:
A moderate \(K_c\) value indicates that the reaction reaches equilibrium with significant amounts of both reactants and products present.
Which of the following reactions has a very large \(K_c\) value and goes almost to completion?
Solution:
The reaction \(2\text{H}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{H}_2\text{O}(g)\) has a very large \(K_c\) value and goes almost to completion because it strongly favors the formation of water.