Q: For the reaction $$2HI(g) \rightleftharpoons H_2$(g) + I_2$(g)$$, if $$K_c = 65.0$$ and the initial concentrations are $$[HI] = 2.80 M$$, $$[H_2$] = 3.40 M$$, $$[I_2$] = 3.40 M$$, what is the value of the reaction quotient $$Q$$?

$$Q = \frac{[H_2$][I_2$]}{[HI]^2} = \frac{3.40 \times 3.40}{(2.80)^2$}$$

Question 1

Which of the following statements best describes chemical equilibrium in a closed system?

Accepted Answer

The forward and reverse reaction rates are equal and the concentrations of reactants and products remain constant over time.

Question 2

For the reaction $$2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)$$, which of the following is true regarding the direction from which equilibrium is approached?

Accepted Answer

Equilibrium is reached regardless of whether the reaction is initiated with reactants or products.

Question 3

Given the general reaction $$aA + bB \rightleftharpoons cC + dD$$, which of the following is the correct expression for the equilibrium constant $$K_c$$?

Accepted Answer

$$K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$$

Question 4

If $$K_c \u003e 1$$ for a reaction, what does this indicate about the equilibrium mixture?

Accepted Answer

Products are favored at equilibrium.

Question 5

Which substances are omitted from the equilibrium constant expression?

Accepted Answer

Pure liquids and solids

Question 6

For the reaction $$A(aq) + 2B(aq) \rightleftharpoons 3C(aq)$$, what is the correct $$K_c$$ expression?

Accepted Answer

$$K_c = \frac{[C]^3}{[A][B]^2}$$

Question 7

A chemist mixes $$0.10 M$$ $$A$$ and $$0.30 M$$ $$B$$ for the reaction $$A(aq) + B(aq) \rightleftharpoons C(aq) + D(aq)$$ with $$K_c = 49.0. $$What is the equilibrium concentration of $$C$$?

Accepted Answer

$$[C] = 0.099 M$$

Question 8

Which mathematical method is required to solve for equilibrium concentrations when the $$K_c$$ expression leads to a quadratic equation?

Accepted Answer

Quadratic formula: $$x = \frac{-b \pm \sqrt{b^2$ - 4ac}}{2a}$$

Question 9

For the reaction $$2HI(g) \rightleftharpoons H_2$(g) + I_2$(g)$$, if $$K_c = 65.0$$ and the initial concentrations are $$[HI] = 2.80 M$$, $$[H_2$] = 3.40 M$$, $$[I_2$] = 3.40 M$$, what is the value of the reaction quotient $$Q$$?

Accepted Answer

$$Q = \frac{[H_2$][I_2$]}{[HI]^2} = \frac{3.40 	imes 3.40}{(2.80)^2$}$$

Question 10

If $$Q \u003c K_c$$ for a reaction, what will happen to the system?

Accepted Answer

The reaction will shift toward the products.

Question 11

Which of the following best explains why equilibrium constants are temperature dependent?

Accepted Answer

Because the rates of forward and reverse reactions change with temperature, affecting the position of equilibrium.

Question 12

Given the van 't Hoff equation $$\ln\left(\frac{K_2$}{K_1$}\right) = -\frac{\Delta H_{rxn}}{R}\left(\frac{1}{T_2$} - \frac{1}{T_1$}\right)$$, which variable represents the universal gas constant?

Accepted Answer

$$R$$

Question 13

A reaction has $$K_c = 4.4 	imes 10^1$ at 25$$^\circ$$C (298$ K) and $$\Delta H_{rxn} = 180,500$$ J/mol. What happens to K_c$ when the temperature is increased to 2400$ K?

Accepted Answer

$$K_c$$ increases

Question 14

In an ICE table for the reaction $$2A + 3B \rightleftharpoons 2C$$, if the initial concentration of $$A is$$ $$0.10 M $$and $$B is$$ $$0.10 M$$, what is the change in concentration for $$B$$ when $$x$$ moles of $$A$$ react?

Accepted Answer

$$-3x$$

Question 15

Why is it important to disregard negative roots when solving for $$x in $$equilibrium calculations using the quadratic formula?

Accepted Answer

Negative roots represent physically impossible negative concentrations.

Question 16

For the reaction $$A(aq) \rightleftharpoons 2C(aq)$$, if the initial concentration of $$A is$$ $$0.25 M $$and $$K_c = 10.0$$, what is the equilibrium concentration of $$C$$?

Accepted Answer

$$[C] = 0.22 M$$

Question 17

Which of the following is a correct real-world application of chemical equilibrium?

Accepted Answer

The synthesis of ammonia in the Haber process, where equilibrium determines the maximum yield.

Question 18

If a system at equilibrium is disturbed by adding more reactant, what will happen according to Le Chatelier's Principle?

Accepted Answer

The system will shift toward the products to re-establish equilibrium.

Question 19

Which of the following is NOT a valid use of the reaction quotient $$Q$$?

Accepted Answer

To calculate the equilibrium constant $$K_c$$ from initial concentrations.

Chapter 16: Chemical Equilibrium – Principles, Calculations, and Applications

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