10-minute Quiz : Chapter 39 Dynamic equilibrium

Which of the following changes is irreversible?

• A. Melting of ice
• B. Dissolution of sugar in water
• C. Cooking of rice
• D. Inflating of a balloon

Which of the following reactions is reversible?

• A. Ionization of water
• B. Combustion of methane
• C. Rusting of iron
• D. Neutralization between hydrochloric acid and sodium hydroxide solution

Consider the chemical equilibrium established in dilute potassium manganate solution (green) at room temperature and pressure. Which of the following statements about the solution is/are correct?

(1) The solution turns purple after a short time.

(2) The pH of the solution is greater than 7.

(3) The rate of consumption of MnO₄²⁻(aq) is equal to the rate of formation of MnO₄⁻(aq).

• A. (1) only
• B. (2) only
• C. (1) and (3) only
• D. (2) and (3) only

Consider the concentration-time graph for a chemical system involving three gases X, Y and Z in a fixed-volume closed container kept at a certain temperature. Which of the following statements concerning this system is/are correct?

(1) At point P, X(g), Y(g) and Z(g) are all present in the system.

(2) At point Q, the system reaches a state of dynamic equilibrium.

(3) At point R, the reaction involving these three gases stops.

• A. (1) only
• B. (2) only
• C. (1) and (3) only
• D. (2) and (3) only

Refer to the experiment on the thermal decomposition of copper(II) carbonate. Upon heating, the green copper(II) carbonate decomposes completely to black copper(II) oxide and colourless carbon dioxide. Which of the following statements correctly explains the result?

• A. It is an irreversible reaction.
• B. Copper(II) oxide is chemically more stable than copper(II) carbonate.
• C. Copper(II) oxide cannot decompose any further.
• D. This reaction is occurring in an open system.

Consider the concentration-time graph for the following reversible reaction:

N₂O₄(g) ⇌ 2NO₂(g)

Which of the following statements concerning this reaction is correct?

• A. At the start of the reaction, only NO₂(g) is present.
• B. The concentration of N₂O₄(g) decreases while that of NO₂(g) increases for the first 20 seconds.
• C. The reaction reaches the state of dynamic equilibrium at the 30ᵗʰ second.

• D. The concentration of N₂O₄(g) is higher than that of NO₂(g) when the reaction is at equilibrium.

In an experiment, 1.0 mol of hydrogen iodide is introduced into a 1.0 dm³ sealed tube maintained at 400°C. The hydrogen iodide decomposes reversibly to form hydrogen and iodine according to the following equation:

2HI(g) ⇌ H₂(g) + I₂(g)

Which of the following statements concerning this reaction is correct?

• A. The rate of the backward reaction is at its minimum at the start of this reversible reaction.
• B. The rate of both the forward and backward reactions decreases as this reversible reaction approaches the state of dynamic equilibrium.
• C. The rate of the forward reaction is at its maximum when this reversible reaction is at equilibrium.
• D. The rate of both the forward and backward reactions is zero when this reversible reaction is at equilibrium.

Equal numbers of moles of N₂(g) and H₂(g) are introduced into a fixed-volume closed container kept at a certain temperature. N₂(g) and H₂(g) undergo a reversible reaction to form NH₃(g), as described by the following equation:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Which of the following correctly shows the relationship regarding the concentrations of N₂(g) and H₂(g) in this reaction when equilibrium is reached?

• A. [H₂(g)] = [N₂(g)]
• B. [H₂(g)] ≤ [N₂(g)]
• C. [H₂(g)] < [N₂(g)]
• D. [H₂(g)] > [N₂(g)]

In a reversible reaction, X(g) decomposes to Y(g) at a given temperature according to the following equation:

X(g) ⇌ 2Y(g)

Given that the concentration of X(g) at the start of the reaction and at equilibrium are 0.8 M and 0.4 M respectively. Which of the concentration-time graphs correctly shows the variation of the concentration of both X(g) and Y(g) over time?

• A
• B
• C
• D

In a reversible reaction, U(g) decomposes to give V(g) in a fixed-volume closed container under certain conditions, as described by the following equation:

U(g) ⇌ V(g)

Which of the graphs shows the possible changes in rates of the forward and backward reactions over time for this reversible reaction?

• A
• B
• C
• D