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Chemical Equilibrium

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Chapter 19Test

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DIREaIONS: Write on the line at the right of each statement the letter preceding the word or expression that bestcompletes the statement.

1. At equilibrium, (a) forward reaction rate is less than reverse reaction rate; (b) forward reactionrate is greater than reverse reaction rate; (c) forward reaction rate is equal to reverse reactionrate; (d) no reactions take place.

2. A reaction in which products can react to re-form reactants is said to be (a) at equilibrium;(b) reversible; (c) buffered; (d) impossible.

3. The chemical equilibrium expression for the equation L + 2M +=! 4N + 30 is K =(a) [N]4[0]3/[L][Mf; (b) [L][M]z/[N]4[0]3;(c) 4[N]3[0]/[L]2[M]; (d) [L]2[M]/4[N]3[0].

4. A very high value of K indicates that (a) equilibrium is reached slowly; (b) products are favored;(c) reactants are favored; (d) equilibrium has been reached.

5. The numerical value of K for a system (a) can be calculated from information on molar masses;(b) can be calculated from information on heat of reaction; (c) can be calculated frominformation on chemical properties; (d) must be obtained experimentally.

6. What is the effect on concentrations if more CO(g) is added to the following equilibriumsystem: 2CO(g) + Oz(g) +=! 2COz(g)? (a) [COz] increases and [Oz] decreases (b) [COz] increasesand [Oz] increases (c) [COz] decreases and [Oz] decreases (d) both [COz] and [Oz] remain thesame

7. What is the effect on concentrations if the temperature of the equilibrium systemCH30H(g) + 101kJ +=! CO(g) + 2Hz(g) is increased? (a) [CH30H] increases and [CO] decreases(b) [CH30H] decreases and [CO] increases (c) [CH30H] increases and [CO] increases(d) there'is no effect

8. Reaction systems that are in equilibrium may be made to run to completion (a) only if they are

not reversible; (b) only if the temperature is low enough; (c) by application of LeChatelier'sprinciple; (d) under no circumstances.

9. Reactions tend to run to completion if a product (a) has a high melting point;(b) is precipitated as a solid; (c) is a liquid; (d) is ionic.

10. The addition of sodium acetate to an acetic acid (HCzH30Z) solution (a) increases pH andlowers [H +]; (b) increases pH and raises [H +]; (c) decreases pH and lowers [H +];(d) decreases pH and raises [H+];

11. In the equilibrium system HCzH30Z(aq) + HzO(t) <=zH30+(aq) + CZH30Z(aq), which of thefollowing is present in the highest concentration? (a) HCzH30Z(b) H30+ (c) CZH30Z(d) The concentrations of HCzH30Z,H30 +, and CZH30Z are all equal.

12. The equilibrium constant K for the ionization of acetic acid HCzH30Z(aq) + HzO(t) <=Z

H30+(aq) + CZH30Z (aq) is equal to (a) [H30+][CzH30z]; (b) [H30+][CzH30Z]/[HCzH30Z][HzOI;(c) [H30+][CzH30zl/[HCzH30zl; (d) [HCzH30z]l[H30+][CzH30zl.

13. How do Ka values for weak and strong acids compare? (a) Ka (weak) = Ka (strong)(b) Ka (weak) < Ka (strong) (c) Ka (weak) > Ka (strong) (d) Ka is not defined for weak acids.

14. The equation for the ionization of water is (a) 2HzO(t) <=Z H30+(aq) + OH-(aq); (b) 2HzO(t) <=Z

H30-(aq) + OH+(aq); (c) 2HzO(t) <=Z 2Hz(aq) + Oz(aq); (d) HzO(t) <=Z H-(aq) + OH+(aq).

15. The value of the ion-product constantfor water is (a) 0; (b) 10 - 14;(c) 10 - 7; (d) 55.4.

16. Addition of the salt of a weak acid to a solution of the weak acid (a) lowers the concentration ofthe nonionized acid and of H30 +; (b) lowers the concentration of the non ionized acid and raisesthe concentration of the H30 +; (c) raises the concentration of the non ionized acid and of H30 +;(d) raises the concentration of the non ionized acid and lowers the concentration of H30 +.

17. If an acid is added to a solution of a weak base and its salt, (a) more water is formed and moreweak base ionizes; (b) hydronium-ion concentration decreases; (c) more hydroxide ion isformed; (d) more nonionized weak base is formed.

Chemical EquilibriumHRW material copyrighted under notice appearing earlier in this work..

Chapter 19 93

18. Solutions that can resist changes in pH are said to be (a) buffered; (b) at equilibrium;(c) neutral; (d) stable.

19. Hydrolysis is a reaction between (a) water molecules; (b) dissolved ions; (c) water and dissolvedions; (d) hydrogen and oxygen.

20. Salts of a weak acid and a strong base produce solutions that are (a) acidic only; (b) basic only;(c) neutral only; (d) either acidic, basic, or neutral.

21. An example of a salt that produces a basic solution is (a) NaCl; (b) NaC2H302; (c) NH4Cl;(d) H20.

22. The symbol for the hydrolysis constant is (a) Ksp; (b) Ka; (c) Kw; (d) Kh.

23. When a CO~- ion reacts with water, the products are (a) HCO; and H30 +; (b) CO2andH30+; (c) HCO; and OH-; (d) H2C03 and H30+.

24. For the salt of a strong acid and a weak base, which of the following occurs?(a) cation hydrolysis only (b) anion hydrolysis only (c) both cation and anion hydrolysis(d) buffer hydrolysis

25. The hydrolysis of Na2C03 involves water and (a) Na+ ions only; (b) CO;- ions only; (c) bothNa+ and CO~- ions; (d) neither Na+ nor CO~- ions.

26. The symbol for the solubility-product constant is (a) K; (b) Kh; (c) Ka; (d) Ksp.

27. If the ion product for a given pair of ions whose solutions have just been mixed is greater thanthe value of Ksp, (a) the solution is unsaturated; (b) precipitation occurs; (c) equilibrium cannotbe achieved; (d) a decomposition reaction occurs.

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DIRECTIONS: Write the answer to questions 28-33 on the line to the right, and show your work in the spaceprovided.

28. Given the chemical equation E + F +:! 2G and the equilibrium concentrations of 0.60 mollLfor E, 0.80 mollL for F, and 1.30 mollL for G, what is the value of the equilibrium constant?

29. What is the concentration of H30+ in a solution of an acid HY that ionizes to giveH30+ and Y- ions, given that Ka = 4.32 X 10-5 and that final concentration ofHY = 7.40 X 10-2 moUL?

30. What is the solubility-product constant of barium carbonate (BaC03), given that the solubilityof this compound is 0.0022 gl100. g water? (atomic masses are: C 12.0111, 0 15.9994, Ba 137.33)

31. What is the solubilty, in mollL, of calcium carbonate (CaC03), given that its Ksp value is1.4 x 10 - 8?

32. What is the solubiIty, in moUL, of copper(I) sulfide (Cu25), given that its Ksp value is6.1 x 1O-49?

33. Calculate the ion product constant for the mixing of 100 mL of 0.000 28 M Pb(N03h with200 mL of 0.0012 M NaCl, given that Ksp for PbCh is 1.9 x 10-4• Will precipitation occur?

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94 Chapter 19 Chemical EquilibriumHRW material copyrighted under notice appearing earlier in this warle