BPGHS SJChO Chemical Equilibrium I

Multiple Choice

1. (Lv.1) Which of the following is the correct K_c expression for the reversible reaction 2HBr(g) --> H₂(g) + Br₂(g)?

• {[H₂(g)][HBr(g)]}/

  {[Br₂(g)]²}

• {2[HBr(g)]}/

  {[H₂(g)]²[Br₂(g)]}

• {[H₂(g)][Br₂(g)]}/

  {[HBr(g)]²}

• {[Br₂(g)][H₂(g)]}/

  {2[HBr(g)]}

Multiple Choice

2. (Lv.1) For the K_c expression derived from question 1, what are the correct K_c units?

• Dimensionless

• mol^-1dm³

• moldm^-3

• mol²dm^-6

Multiple Choice

3. (Lv.2) When aqueous ammonia, NH₃(aq) is added to Zinc Hydroxide, Zn(OH₂) in large excess, a miraculous phenomenon occurs where the precipitate dissolves! The reversible equilibrium is given by: Zn(OH)₂(s) + 4NH₃(aq) --> Zn(NH₃)₄²⁺(aq) + 2OH^-(aq). What is the correct K_c expression for the above dissolution reaction?

• {[NH₃(aq)]⁴[OH^-(aq)]²}/

  {[Zn(NH₃)₄²⁺(aq)]²[Zn(OH)₂(s)]}

• {4[NH₃(aq)]}/{[Zn(NH₃)₄²⁺(aq)][OH^-(aq)]²}

• {[Zn(NH₃)₄²⁺(aq)][OH^-(aq)]²}/

  {[NH₃(aq)]⁴}

• {[Zn(OH)₂(s)][Zn(NH₃)₄²⁺(aq)]}/{[NH₃(aq)]⁴[OH^-(aq)]²}

Multiple Choice

4. (Lv. 1) For the K_c expression derived from question 3, what are the correct K_c units?

• Dimensionless

• mol²dm-⁶

• moldm^-3

• mol^-1dm³

Multiple Choice

5. (Lv. 2) A metal displacement reaction occurs when a more reactive metal is exposed to a "salt solution" of the less reactive metal. For a solution of Iron(III) Nitrate, Zinc metal was added, prompting such a reaction to take place. By means of writing the ionic equation for this displacement reaction, derive the K_c expression for this particular metal displacement reaction.

• {[Fe(s)]²}/

  {[Zn²⁺(aq)]³}

• {[Zn²⁺(aq)]³}/

  {[Fe³⁺(aq)]²}

• {2[Fe(s)]}/

  {[Zn(s)]³}

• {[Zn²⁺(aq)]³[Fe(s)]²}/

  {[Fe³⁺(aq)]²[Zn(s)]³}

Answer/Feedback:

Ionic equation: 3Zn(s) + 2Fe³⁺(aq) --> 3Zn²⁺(aq) + 2Fe(s).

Solids are not included into the K_c expression.

Do make it a point to write your state symbols so that you know clearly what to include and what to exclude from K_c!

Multiple Choice

6. (Lv. 1) For the K_c expression derived from question 5, what are the correct K_c units?

• Dimensionless

• moldm^-3

• mol2dm^-6

• mol³dm^-9

Multiple Choice

7. (Lv. 1) In an experiment to study the formation of Hydrogen Iodide, I₂(g) + H₂(g) --> 2HI(g), the equilibrium concentrations of I₂(g), H₂(g) and HI(g) were 1.06x10^-3moldm^-3, 6.50x10^-5moldm^-3 and 1.80x10^-3moldm^-3 respectively. Calculate the K_c of this equilibrium reaction, assuming no temperature changes.

• 47

• 0.212

• 26125

• 6.856

Answer/Feedback:

Multiple Choice

8. (Lv. 2) At a certain temperature, the value of K_c for the equilibrium system HCN(aq) + H₂O(l) --> CN^-(aq) + H₃O⁺(aq) is 6.20x10^-10moldm^-3. What is the new K_c value for the following reaction: 2HCN(aq) + 2H₂O(l) --> 2CN^-(aq) + 2H₃O⁺(aq)?

• 1.24x10^-9moldm^-3

• 3.84x10^-19mol²dm^-6

• 2.49x10^-5mol²dm^-6

• 1.24x10^-9

Answer/Feedback:

Multiple Choice

9. (Lv. 2) 2 equilibria are as shown below:

Equilibria I: 2X₂(g) + Y₂(g) --> 2X₂Y

Equilibria II: X₂Y --> X₂(g) + 1/2Y₂(g)

If the value of K_c for the 1st equilibria is 2M, under the same conditions of temperature, what is the value of K_c for equilibria II?

• 0.707M^-1/2

• 0.500M^-1

• -0.250M

• 1M²

Answer/Feedback:

Since the reaction is reversed, by writing the reverse K_c expression, you can see that it is an inverse of the original K_c. Moreover, the moles of each of the chemical entities are divided by 1/2 - these will be raised to the powers. This means that a square root is needed too. The final answer should be 1/sqrt(2).

Multiple Choice

10. (Lv. 2) At a certain temperature, the dissolution of 1 mole of AgCl(s) in an aqueous medium has a K_c value of 1.60x10^-10mol²dm^-6. What is the value of K_c for the precipitation of 4 moles of AgCl(s) from its constituent (aq) ions?

• 2.81x10²mol²dm^-6

• 6.4x10^-10moldm^-3

• 6.55x10^-32mol⁴dm^-12

• 1.53x10³⁹mol^-8dm²⁴

Answer/Feedback:

Multiple Choice

11. (Lv. 2) A chemist employed by the National Environment Agency (NEA) is tasked to study catalytic converters in relation to urban smog. The chemist is tasked to find K_c for the following equilibrium reaction: 2NO₂(g) --> 2O₂(g) + N₂(g)

Given the following data:

2NO₂(g) --> 2NO(g) + O₂(g) K_c=1.10x10^-5moldm^-3

0.5O₂(g) + 0.5N₂(g) --> NO(g) K_c=4.80x10^-10

Calculate unknown K_c for the reaction that the chemist is tasked to study.

• 1.59x10^-12mol^-1dm³

• 2.29x10⁴moldm^-3

• 4.77x10¹³moldm^-3

• 0.000011mol^-1dm³

Answer/Feedback:

Multiple Choice

12. (Lv. 2) The depletion of ozone in the upper atmosphere is a very pressing environmental issue. The overall equation is O₃(g) --> O(g) + O₂(g).

Given the following data:

NO₂(g) --> NO(g) + O(g) K_c=7.80x10^-45moldm^-3

NO₂(g) + O₂(g) --> NO(g) + O₃(g) K_c=1.70x10³³

Calculate the unknown K_c for the depletion of ozone.

• 4.59x10^-78moldm^-3

• 2.29x10^-52moldm^-3

• 1.326x10^-11moldm^-3

• 3.83x10^-36moldm^-3

Answer/Feedback:

Multiple Choice

13. (Lv. 3) At temperature TK, 3 equilibrium constants for their respective equilibrium systems are as shown below:

CO₂(g) + H₂(g) --> CO(g) + H₂O(g) K₁=0.2

C(s) + CO2(g) --> 2CO(g) K₂= 6.2moldm^-3

C(s) + 1/2O₂(g) --> CO(g) K₃=3.30x10⁴(moldm^-3)^0.5

Using the above, what is the value of K_c for the following equilibrium: 3CO₂(g) + H₂(g) --> 3CO(g) + H₂O(g) + O₂(g) at temperature TK?

• 1.67x10^-7mol^-1dm³

• 2.70x10^-8

• 7.06x10^-9moldm^-3

• 4.09x10^-4mol²dm^-6

Answer/Feedback:

Multiple Choice

14. (Lv. 1) Calcium Carbonate, CaCO₃ readily decomposes upon heating to give solid calcium oxide and gaseous carbon dioxide. Which of the following is the correct expression for K_p?

• P_CO2(g)

• {P_CO2(g)P_CaO(s)}/

  P_CaCO3(s)

• 1/{P_CO2(g)²}

• It is not possible to have an expression for K_p in this scenario.

Multiple Choice

15. (Lv. 1) For the K_p expression derived from question 13, what are the correct K_p units?

• atm

• atm-1

• atm2

• atm^-2

Multiple Choice

16. (Lv. 1) For the following reversible reaction: 4NH₃(g) + 7O₂(g) --> 4NO₂(g) + 6H₂O(l), what is the correct K_p expression?

• {P_NO2(g)⁴6P_H2O(l)}/{P_O2(g)⁷}

• {P_NO2(g)⁴}/

  {P_NH3(g)⁴P_O2(g)⁷}

• {P_NH3(g)⁴P_O2(g)⁷}/

  {P_NO2(g)⁴P_H2O(l)⁶}

• {P_NH3(g)⁴P_NO2(g)⁴}/{P_O2(g)⁷}

Multiple Choice

17. (Lv. 1) For the K_p expression derived from question 14, what are the correct K_p units?

• Pa⁴

• Pa^-3

• Pa^-7

• Pa

Multiple Choice

18. (Lv. 2) Calculate K_p for the reaction 2IF₃(s) + 3Ne(g) --> 3NeF₂(s) + I₂(s), given that the equilibrium amounts of Ne, NeF₂ and I₂ are all the same, while Ne exerts a pressure of 2.90kPa at equilibrium.

• 2900Pa

• 4.10x10^-2Pa

• 2.44x10¹⁰Pa^-1

• 4.10x10^-11Pa^-3

Answer/Feedback:

Multiple Choice

19. (Lv. 2) At 1000^oC, the following reaction C(s) + 2H₂(g) --> CH₄(g) has K_p of 0.262atm^-1. At equilibrium, the partial pressure of Methane is 12.2kPa. What is the equilibrium partial pressure of Hydrogen?

• 21.40kPa

• 0.459atm

• 6.82kPa

• 0.678atm

Answer/Feedback:

Multiple Choice

20. (Lv. 2) At a certain temperature, the value of K_p for the reversible equilibrium reaction 3O₂(g) --> 2O₃(g) is 8.00atm^-1. What is the value of K_p for the following reaction: 2O₃(g) --> 3O₂(g)?

• 0.583

• 2.828atm²

• 2.000atm^-1

• 0.125atm

Answer/Feedback:

Multiple Choice

21. (Lv. 2) A gaseous equilibrium mixture in a flask at temperature T was found to consist of 0.50mol of SO₂(g), 0.12mol of O₂(g) and 5.0mol of SO₃(g). The total pressure inside the flask was 800kPa.

• 5.85kPa^-1

• 0.584kPa^-1

• 8.15kPa^-1

• 6.44kPa^-1

Answer/Feedback:

Multiple Choice

22. (Lv. 1) The water-gas shift reaction plays a central role in the chemical methods for obtaining cleaner fuels from coal. The reaction is given by: CO(g) + H₂O(g) --> H₂(g) + CO₂(g). At a temperature of TK, the K_p is 2.7. Calculate the value of K_c for the same reaction.

• 1.643

• 2.700

• 4.436

• 3.554

Answer/Feedback:

K_p=K_c(RT)^2-2, so (RT)⁰ = 1, thus, K_p = K_c.

Multiple Choice

23. (Lv. 1) 2.00moles each of SO₂(g), SO₃(g) and O₂(g) are mixed and allowed to react in a 2l container. If the K_c of the reaction: 2SO₂(g) + O₂(g) --> 2SO₃(g) is 0.8moldm^-3, what will happen to the chemical system in this current state?

• The backward rate will be favoured.

• The forward rate will be favoured.

• There will be no net changes in the current position of equilibrium.

• Impossible to predict as there is not enough data.

Answer/Feedback:

Multiple Choice

24. (Lv. 1) At 425^oC, for the following reaction 2HBr(g) --> H₂(g) + Br₂(g), K_p=4.18x10^-9. In 1 experiment, 1.00atm of HBr(g), 0.010atm of H₂(g) and 0.010atm of Br₂(g) were introduced into a reaction vessel. What will happen to this chemical system?

• Position of equilibrium will shift to the reactants.

• Position of Equilibrium will shift to the products.

• The system is at equilibrium, so there will be no net changes that take place.

• All 3 aforementioned options will occur.

Answer/Feedback:

Multiple Choice

25. (Lv. 1) At room temperature, the equilibrium constant, K_c for the following reaction 2NO(g) --> O₂(g) + N₂(g) is 1.4x10³⁰. 560g of N₂(g) was mixed with 320g of O₂(g) and 90g of NO(g). What will happen to this chemical system?

• Position of equilibrium shifts to the right.

• Position of equilibrium shifts to the left.

• The chemical system is in equilibrium, so no net changes will occur.

• Impossible to tell, as the total volume of the chemical system is not given - i.e., concentration of each of the chemicals are unknown.

Answer/Feedback:

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