Q: For the reaction $$\mathrm{A(g) \rightleftharpoons B(g)}$$, which set of values is most appropriate for using the 'x is small' approximation?

$$K = 1.0 \times 10$$^{-5}$$;\ [A]_\text{initial} = 0.250\ \mathrm{M}$$

Q: A student is solving for the equilibrium concentration of $$\mathrm{S_2$} in $$the reaction $$2\mathrm{H_2S(g)} \rightleftharpoons 2\mathrm{H_2$(g)} + \mathrm{S_2$(g)}$$ with a very small $$K_c. $$The initial $$[\mathrm{H_2S}] is$$ $$0.0250\ \mathrm{M}. $$The student uses the 'x is small' approximation and finds $$x = 2.97 \times 10$$^{-4}$$. How should the student check if the approximation is valid?

Calculate $$\dfrac{x}{[\mathrm{H_2S}]_\text{initial}} \times 100\%$$ and confirm it is less than 5%.

Question 1

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)} at$$ $$445^\circ\mathrm{C}$$, the equilibrium constant $$K_c is 50. If $$the equilibrium concentrations are $$[\mathrm{H_2$}] = 0.11\ \mathrm{M}$$, $$[\mathrm{I_2$}] = 0.11\ \mathrm{M}$$, and $$[\mathrm{HI}] = 0.78\ \mathrm{M}$$, which of the following correctly expresses the equilibrium constant for this reaction?

Accepted Answer

$$K_c = \dfrac{[\mathrm{HI}]^2}{[\mathrm{H_2$}][\mathrm{I_2$}]}$$

Question 2

A reaction mixture at $$445^\circ\mathrm{C}$$ contains $$[\mathrm{H_2$}] = 0.33\ \mathrm{M}$$ and $$[\mathrm{I_2$}] = 0.165\ \mathrm{M} at $$equilibrium. If $$K_c = 50$$ for $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, what is the equilibrium concentration of HI?

Accepted Answer

$$[\mathrm{HI}] = 1.65\ \mathrm{M}$$

Question 3

For the reaction $$\mathrm{A(g) \rightleftharpoons 2B(g)}$$ with $$K_c = 4.0$$, if $$[\mathrm{A}] = 1.0\ \mathrm{M} at $$equilibrium, what is $$[\mathrm{B}]$$?

Accepted Answer

$$[\mathrm{B}] = 2.0\ \mathrm{M}$$

Question 4

Given the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}$$ and the following equilibrium concentrations: $$[\mathrm{CO}] = 0.15\ \mathrm{M}$$, $$[\mathrm{H_2$}] = 0.30\ \mathrm{M}$$, $$[\mathrm{CH_3OH}] = 0.35\ \mathrm{M}$$, what is the value of $$K_c$$?

Accepted Answer

$$K_c = 26$$

Question 5

For the generic reaction $$aA + bB \rightleftharpoons cC + dD$$, the reaction quotient $$Q_c is $$given by:

Accepted Answer

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

Question 6

A mixture of $$\mathrm{N_2O_4(g)}$$ and $$\mathrm{NO_2$(g)}$$ has $$P_{\mathrm{N_2O_4}} = 1\ \mathrm{atm}$$ and $$P_{\mathrm{NO_2$}} = 1\ \mathrm{atm} at a $$temperature where $$K = 0.15$$ for $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}. $$What is true about the direction the reaction will proceed?

Accepted Answer

Q \u003e K; the reaction will proceed to the left.

Question 7

If $$Q \u003c K$$ for a chemical reaction, what will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will proceed in the forward direction, increasing the concentration of products.

Question 8

For the reaction $$\mathrm{A(g) \rightleftharpoons B(g)}$$, which set of values is most appropriate for using the 'x is small' approximation?

Accepted Answer

$$K = 1.0 	imes 10$$^{-5}$$;\ [A]_	ext{initial} = 0.250\ \mathrm{M}$$

Question 9

A student is solving for the equilibrium concentration of $$\mathrm{S_2$} in $$the reaction $$2\mathrm{H_2S(g)} ightleftharpoons 2\mathrm{H_2$(g)} + \mathrm{S_2$(g)}$$ with a very small $$K_c. $$The initial $$[\mathrm{H_2S}] is$$ $$0.0250\ \mathrm{M}. $$The student uses the 'x is small' approximation and finds $$x = 2.97 	imes 10$$^{-4}$$. How should the student check if the approximation is valid?

Accepted Answer

Calculate $$\dfrac{x}{[\mathrm{H_2S}]_	ext{initial}} 	imes 100\%$$ and confirm it is less than 5%.

Question 10

In a real-world scenario, the synthesis of methanol is important for fuel production. For the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}$$, if the initial concentrations are $$[\mathrm{CO}] = 0.27\ \mathrm{M}$$, $$[\mathrm{H_2$}] = 0.49\ \mathrm{M}$$, and at equilibrium $$[\mathrm{CH_3OH}] = 0.11\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{CO}$$?

Accepted Answer

$$[\mathrm{CO}] = 0.16\ \mathrm{M}$$

Question 11

Which of the following statements about equilibrium constants is correct?

Accepted Answer

The value of the equilibrium constant is independent of the initial amounts of reactants and products, as long as temperature is constant.

Question 12

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, if $$K = 0.15$$ and the initial partial pressures are $$P_{\mathrm{N_2O_4}} = 1\ \mathrm{atm}$$ and $$P_{\mathrm{NO_2$}} = 0.1\ \mathrm{atm}$$, what is the value of $$Q$$ and which direction will the reaction proceed?

Accepted Answer

$$Q = 0.01$$; Q \u003c K, so the reaction will proceed to the right.

Question 13

A chemical engineer is designing a process to maximize the yield of $$\mathrm{HI} in $$the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}. $$Which of the following strategies will increase the equilibrium concentration of $$\mathrm{HI}$$, assuming temperature is constant?

Accepted Answer

Increase the initial concentrations of $$\mathrm{H_2$}$$ and $$\mathrm{I_2$}.$$

Question 14

For the reaction $$\mathrm{A(g) \rightleftharpoons B(g)}$$ with $$K = 1.45$$, if $$[A] = 0.25\ \mathrm{M}$$ and $$[B] = 0.10\ \mathrm{M}$$, what is the value of $$Q$$ and what does it indicate?

Accepted Answer

$$Q = 0.40$$; Q \u003c K, so the reaction will proceed to the right.

Question 15

A reaction mixture contains $$[\mathrm{CO}] = 0.20\ \mathrm{M}$$, $$[\mathrm{H_2$}] = 0.40\ \mathrm{M}$$, and $$[\mathrm{CH_3OH}] = 0.10\ \mathrm{M}$$ for the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}. If$$ $$K_c = 0.20$$, what is the value of $$Q$$ and which direction will the reaction proceed?

Accepted Answer

$$Q = 3.13$$; Q \u003e K, so the reaction will proceed to the left.

Question 16

In a medical scenario, carbon monoxide poisoning can be treated by increasing the concentration of oxygen. For the equilibrium $$\mathrm{COHb \rightleftharpoons CO + Hb}$$, what effect does increasing $$[\mathrm{O_2$}]$$ have on the equilibrium position?

Accepted Answer

It shifts the equilibrium to the left, reducing $$[\mathrm{COHb}].$$

Question 17

Which of the following best describes the use of an ICE table in equilibrium calculations?

Accepted Answer

It organizes initial concentrations, changes, and equilibrium concentrations to systematically solve for unknowns.

Chemical Equilibrium: Calculating Equilibrium Constants and Concentrations

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드