Reaction quotient (Q) Knowledge-Based Download PDF

Questions

1. 1.

   Which statement correctly distinguishes the reaction quotient ($Q$) from the equilibrium constant ($K$) for a reversible chemical system?

   • A) The reaction quotient $Q$ is determined solely by the initial concentrations of reactants, whereas $K$ varies continuously as the reaction proceeds.
   • B) The reaction quotient $Q$ remains constant at a fixed temperature, whereas $K$ changes whenever concentrations are altered.
   • C) The mathematical expression for $Q$ incorporates pure solids and liquids, whereas the expression for $K$ excludes them.
   • D) The reaction quotient $Q$ is evaluated using instantaneous concentrations at any given point, whereas $K$ is evaluated strictly using equilibrium concentrations.
2. 2.

   For a reversible gaseous reaction, the reaction quotient is determined to be less than the equilibrium constant ($Q_c < K_c$) at a given temperature. Which statement correctly describes the relationship between the forward and reverse reaction rates at this moment, and the net direction in which the reaction proceeds to reach dynamic equilibrium?

   • A) The reverse reaction rate is greater than the forward reaction rate, and the reaction proceeds in the reverse direction to consume products.
   • B) The forward and reverse reaction rates are equal, and the system remains at dynamic equilibrium with no net concentration change.
   • C) The forward reaction rate is greater than the reverse reaction rate, and the reaction proceeds in the forward direction to form more products.
   • D) The forward reaction rate is greater than the reverse reaction rate, and the reaction proceeds in the reverse direction to form more reactants.
3. 3.

   A gaseous mixture for the reaction $\text{CO}(g) + \text{Cl}_2(g) \rightleftharpoons \text{COCl}_2(g)$ is initially at dynamic equilibrium in a closed vessel. If the volume of the vessel is suddenly doubled at constant temperature, which statement correctly describes the immediate value of the reaction quotient ($Q_c$) relative to $K_c$ and the direction the system shifts to restore equilibrium?

   • A) $Q_c$ becomes half of $K_c$, so the reaction shifts toward the products.
   • B) $Q_c$ remains equal to $K_c$, so the system remains at equilibrium.
   • C) $Q_c$ becomes twice $K_c$, so the reaction shifts toward the reactants.
   • D) $Q_c$ becomes four times $K_c$, so the reaction shifts toward the reactants.
4. 4.

   How does the reaction quotient ($Q_c$) change over time in a closed vessel where a reversible reaction begins with only reactants present, and what is its value when dynamic equilibrium is achieved?

   • A) It decreases continuously from an infinite value until it reaches $K_c$ at dynamic equilibrium.
   • B) It remains constant at zero during the reaction and abruptly shifts to $K_c$ at dynamic equilibrium.
   • C) It decreases continuously from $K_c$ to zero as reactants are consumed to form products.
   • D) It increases continuously from zero until it equals $K_c$ at dynamic equilibrium.
5. 5.

   For the gaseous reaction $\text{PCl}_3(g) + \text{Cl}_2(g) \rightleftharpoons \text{PCl}_5(g)$, the equilibrium constant is $K_c = 4.0$ at a given temperature. If the instantaneous concentrations in a reaction vessel are $[\text{PCl}_3] = 0.20\text{ M}$, $[\text{Cl}_2] = 0.10\text{ M}$, and $[\text{PCl}_5] = 0.16\text{ M}$, what is the value of the reaction quotient ($Q_c$) and in which direction will the reaction proceed to reach equilibrium?

   • A) $Q_c = 8.0$; the reaction will proceed toward the reactants (to the left).
   • B) $Q_c = 8.0$; the reaction will proceed toward the products (to the right).
   • C) $Q_c = 0.125$; the reaction will proceed toward the products (to the right).
   • D) $Q_c = 0.125$; the reaction will proceed toward the reactants (to the left).