Химия на английском. 2

5.DYNAMIC CHEMICAL EQUILIBRIUM

5.1.Write the equilibrium expression for each homogeneous reaction.

a)The reaction between nitrogen gas and oxygen gas at high temperatures:

N2(g) + O2(g) 2 NO(g).

b) The reaction between hydrogen gas and oxygen gas to form water vapour:

2 H2(g) + O2(g) 2 H2O(g).

c) The reduction-oxidation equilibrium of iron and iodine ions in aqueous solution:

2 Fe3+(aq) + 2 I–(aq) 2 Fe2+(aq) + I2(aq). d) The oxidation of ammonia:

4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g).

5.2.Write equilibrium constant expressions for these equilibria.

a)N2O4(g) 2 NO2(g);

b) CO(g) + 3 H2(g) CH4(g) + H2O(g);

c)2 H2S(g) 2 H2(g) + S2(g).

5.3.Write equilibrium constant expressions for these heterogeneous equilibria.

a)C10H8(s) C10H8(g);

b)CaCO3(s) CaO(s) + CO2(g);

c)H2O(l) H2O(g);

d)C(s) + H2O(g) CO(g) + H2(g);

e)FeO(s) + CO(g) Fe(s) + CO2(g).

5.4.Three reactions, and their equilibrium constants, are given below.

Arrange these reactions in the order of their tendency to form products.

5.5.Identify each reaction as essentially going to completion or not taking place.

a)N2(g) + 3 Cl2(g) 2 NCl3(g); Keq = 3.0 1011.

b) 2 CH4(g) C2H6(g) + H2(g); Keq = 9.5 10–13.

c) 2 NO(g) + 2 CO(g) N2(g) + 2 CO2(g); Keq = 2.2 1059.

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5.6. Most metal ions combine with other ions in solution. For example, in aqueous ammonia, silver(I) ions are at equilibrium with different complex ions.

[Ag(H2O)2]+(aq) + 2 NH3(aq) [Ag(NH3)2]+(aq) + 2 H2O(l).

At room temperature, Keq for this reaction is 1 107. Which of the two silver complex ions is more stable? Explain your reasoning.

5.7. Consider the following reaction: H2(g) + Cl2(g) 2 HCl(g). Its equilibrium

constant Keq = 2.4 1033 at 25 oC. HCl(g) is placed in a reaction vessel. To what extent do you expect the equilibrium mixture to dissociate into H2(g) and Cl2(g)?

5.8. The following reaction took place in a sealed flask at 250°C: PCl5(g) PCl3(g) + Cl2(g).

At equilibrium, the gases in the flask had the following concentrations:

[PCl5] = 1.2 10–2 mol/L, [PCl3] = 1.5 10–2 mol/L, and [Cl2] = 1.5 10–2 mol/L. Calculate the value of Keq at 250°C.

5.9. Iodine and bromine react to form iodine monobromide, IBr. I2(g) + Br2(g) 2 IBr(g).

At 250°C, an equilibrium mixture in a 2.0 L flask contained 0.024 mol of I2(g), 0.050 mol of Br2(g), and 0.38 mol of IBr(g). What is the value of Keq for the reaction?

5.10.At high temperatures, carbon dioxide gas decomposes into carbon monoxide and

oxygen gas. At equilibrium, the gases have the following concentrations: [CO2(g)] = = 1.2 mol/L, [CO(g)] = 0.35 mol/L, and [O2(g)] = 0.15 mol/L. Determine Keq at the temperature of the reaction.

5.11.Hydrogen sulfide is a pungent, poisonous gas. At 1400 K, an equilibrium mixture

was found to contain 0.013 mol/L hydrogen, 0.046 mol/L sulfur in the form of S2(g), and 0.18 mol/L hydrogen sulfide. Calculate the equilibrium constant, at 1400 K, for the

following reaction: 2 H2S(g) 2 H2(g) + S2(g).

5.12. Methane, ethyne, and hydrogen form the following equilibrium mixture:

2 CH4(g) C2H2(g) + 3 H2(g).

While studying this reaction mixture, a chemist analyzed a 4.0 L sealed flask at 1700°C. The chemist found 0.46 mol of CH4(g), 0.64 mol of C2H2(g), and 0.92 mol of H2(g). What is the value of Keq for the reaction at 1700°C?

5.13. Sulfur atoms combine to form molecules that have different numbers of atoms depending on the temperature. At about 1050°C, the following dissociation occurs:

S8(g) 4 S2(g).

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The initial concentration of S8(g) in a flask is 9.2 10−3 mol/L, and the equilibrium concentration of the same gas is 2.3 10−3 mol/L. What is the value of Keq?

5.14. Consider an equilibrium in which oxygen gas reacts with gaseous hydrogen chloride to form gaseous water and chlorine gas. At equilibrium, the gases have the following concentrations: [O2] = 8.6 10−2 mol/L, [HCl] = 2.7 10−2 mol/L, [H2O] =

=7.8 10−3 mol/L, [Cl2] = 3.6 10−3 mol/L.

a)Write a balanced chemical equation for this reaction.

b)Calculate the value of the equilibrium constant.

5.15. Calculate Keq for the equilibrium:

N2O4(g) 2 NO2(g),

using the data [N2O4] = 0.0185 mol/L and [NO2] = 0.0627 mol/L.

5.16. Calculate Keq for the equilibrium:

CO(g) + 3 H2(g) CH4(g) + H2O(g),

using the data [CO] = 0.0613 mol/L, [H2] = 0.1839 mol/L, [CH4] = 0.0387 mol/L, and [H2O] = 0.0387 mol/L.

5.17 Determine the value of equilibrium constant at 400 K for the decomposition of phosphorus pentachloride, if [PCl5] = 0.135 mol/L, [PCl3] = 0.550 mol/L, and [Cl2] =

= 0.550 mol/L. The equation for the reaction is: PCl5(g) PCl3(g) + Cl2(g).

5.18. At 25 °C, the value of Keq for the following reaction is 82. I2(g) + Cl2(g) 2 ICl(g).

0.83 mol of I2(g) and 0.83 mol of Cl2(g) are placed in a 10 L container at 25 °C. What are the concentrations of the three gases at equilibrium?

5.19. At a certain temperature, Keq = 4.0 for the following reaction: 2 HF(g) H2(g) + F2(g).

A 1.0 L reaction vessel contained 0.045 mol of F2(g) at equilibrium. What was the initial amount of HF in the reaction vessel?

5.20. A chemist was studying the following reaction:

SO2(g) + NO2(g) NO(g) + SO3(g).

In a 1.0 L container, the chemist added 0.17 mol of SO2 to 0.11 mol of NO2. The value of Keq for for the reaction at a certain temperature is 4.8. What is the equilibrium concentration of SO3 at this temperature?

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5.21. Phosgene, COCl2, is an extremely toxic gas. It is prepared by mixing carbon monoxide and chlorine gas:

CO(g) + Cl2(g) COCl2(g).

0.055 mol of CO and 0.072 mol of Cl2 are placed in a 5.0 L container. At 870 K, the equilibrium constant is 0.20. What are the equilibrium concentrations of the mixture?

5.22. Hydrogen bromide decomposes at 700 K.

2 HBr(g) H2(g) + Br2(g); Keq = 4.2 10–9.

0.090 mol of HBr is placed in a 2.0 L reaction vessel and heated to 700 K. What is the equilibrium concentration of each gas?

5.23. The following equation represents the equilibrium reaction for the dissociation of phosgene gas: COCl2(g) CO(g) + Cl2(g). At 100 °C, the value of Keq for this

reaction is 2.2 10−8. The initial concentration of COCl2 in a closed container at 100 °C is 1.5 mol/L. What are the equilibrium concentrations of CO and Cl2?

5.24.Hydrogen sulfide dissociates into hydrogen and sulfur in gaseous state at 1400 °C,

with Keq equal to 2.4 10−4. Suppose, 4.0 mol of H2S is placed in a 3.0 L container. What is the equilibrium concentration of H2 at 1400°C?

5.25.At a certain temperature, the value of Keq for the following reaction is 3.3 10–12.

2 NCl3(g) N2(g) + 3 Cl2(g).

A certain amount of nitrogen trichloride, NCl3, is put in a 1.0 L reaction vessel at this temperature. At equilibrium, 4.6 10−4 mol of N2 is present. What amount of NCl3 was put in the reaction vessel?

5.26. At a certain temperature, the value of Keq for the following reaction is 4.2 10–8. N2(g) + O2(g) 2 NO(g).

0.45 mol of N2 and 0.26 mol of O2 are put in a 6.0 L reaction vessel. What is the equilibrium concentration of NO at this temperature?

5.27. At a particular temperature, Keq for the decomposition of carbon dioxide gas equals 2.0 10–6.

2 CO2(g) 2 CO(g) + O2(g).

3.0 mol of CO2 is put in a 5.0 L container. Calculate the equilibrium concentration of each gas.

5.28. 0.50 mol of CO and 0.50 mol of H2O are placed in a 10 L container at 700 K. The following reaction occurs: CO(g) + H2O(g) H2(g) + CO2(g); Keq = 8.3.

What is the concentration of each gas that is present at equilibrium?

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5.29. At a certain temperature, Keq = 10.5 for the equilibrium CO(g) + 2 H2(g) CH3OH(g).

Calculate these concentrations:

a)[CO] in an equilibrium mixture with 0.933 mol/L H2 and 1.32 mol/L CH3OH;

b)[H2] in an equilibrium mixture with 1.09 mol/L CO and 0.325 mol/L CH3OH;

c)[CH3OH] in an equilibrium mixture with 0.0661 mol/L H2 and 3.85 mol/L CO.

5.30. Equilibrium constant is 1.60 at 933 K for this reaction: H2(g) + CO2(g) H2O(g) + CO(g).

Calculate the equilibrium concentration of hydrogen when [CO2] = 0.320 mol/L, [H2O] = 0.240 mol/L, and [CO] = 0.280 mol/L.

5.31. At 2273 K, Keq = 6.2 10–4 for the reaction:

N2(g) + O2(g) 2 NO(g).

If [N2] = 0.05200 mol/L and [O2] = 0.00120 mol/L, what is the concentration of NO at equilibrium?

5.32.How would decreasing the volume of the reaction vessel affect these equilibria?

a)2 SO2(g) + O2(g) 2 SO3(g).

b)H2(g) + Cl2(g) 2 HCl(g).

c)2 NOBr(g) 2 NO(g) + Br2(g).

5.33.Use Le Chatelier’s principle to predict how each of these changes would affect the ammonia equilibrium system:

N2(g) + 3 H2(g) 2 NH3(g);

a)removing hydrogen from the system;

b)adding ammonia to the system;

c)adding hydrogen to the system.

5.34.In the following equilibrium, would you raise or lower the temperature to obtain these results?

C2H2(g) + H2O(g) CH3CHO(g); H° = –151 kJ;

a)an increase in the amount of CH3CHO;

b)a decrease in the amount of C2H2;

c)an increase in the amount of H2O.

5.35.Predict how this equilibrium would respond to a simultaneous increase in both temperature and pressure.

CO(g) + Cl2(g) COCl2(g); H° = –220 kJ.

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5.36. Use Le Chatelier’s principle to predict how each of the following changes would affect this equilibrium:

H2(g) + CO2(g) H2O(g) + CO(g);

a)adding H2O(g) to the system;

b)removing CO(g) from the system;

c)adding H2(g) to the system;

d)adding something to the system to absorb CO2(g).

5.37.How would increasing the volume of the reaction vessel affect these equilibria?

a)NH4Cl(s) NH3(g) + HCl(g).

b)N2(g) + O2(g) 2 NO(g).

5.38.How would decreasing the volume of the reaction vessel affect these equilibria?

a) 2 N2H4(g) + 2 NO2(g) 3 N2(g) + 4 H2O(g).

b)2 H2O(g) 2 H2(g) + O2(g).

5.39.How would these equilibria be affected by increasing the temperature?

a) 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) + heat.

b)heat + NaCl(s) Na+(aq) + Cl–(aq).

5.40.Ethylene (C2H4) reacts with hydrogen to form ethane (C2H6):

C2H4(g) + H2(g) C2H6(g) + heat.

How would you regulate the temperature of this equilibrium to do the following?

a)increase the yield of ethane;

b)decrease the concentration of ethylene;

c)increase the amount of hydrogen in the system.

5.41.How would simultaneously decreasing the temperature and volume of the system affect these equilibria?

a)heat + CaCO3(s) CaO(s) + CO2(g).

b)4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) + heat.

5.42.Consider the following reaction: H2(g) + I2(g) + 52 kJ 2 HI(g). In which direction does the equilibrium shift if there is an increase in temperature?

5.43.Why does changing the volume of the reaction vessel have no effect on this equilibrium?

CO(g) + Fe3O4(s) CO2(g) + 3 FeO(s).

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5.44.A decrease in the pressure of each system below is caused by increasing the volume of the reaction container. In which direction does the equilibrium shift?

a)CO2(g) + H2(g) CO(g) + H2O(g).

b)2 NO2(g) N2O4(g).

c)2 CO2(g) 2 CO(g) + O2(g).

d)CH4(g) + 2 H2S(g) CS2(g) + 4 H2(g).

5.45.For each reversible reaction, determine whether the forward reaction is favored by high temperatures or low temperatures.

a) N2O4(g) 2 NO2(g); H = +59 kJ.

5.46. The following reaction is exothermic: 2 NO(g) + 2 H2(g) N2(g) + 2 H2O(g). In which direction does the equilibrium shift as a result of each change?

a)removing the hydrogen gas;

b)increasing the pressure of gases in the reaction vessel by decreasing the

volume;

c)increasing the pressure of gases in the reaction vessel by pumping in argon gas while keeping the volume of the vessel constant;

d)increasing the temperature;

e)using a catalyst.

5.47.In which direction does the equilibrium shift as a result of the change to each homogeneous equilibrium system?

a)Adding Cl2(g): 2 Cl2(g) + O2(g) 2 Cl2O(g).

b) Removing N2(g): 2 NO2(g) N2(g) + 2 O2(g).

c) Using a catalyst: CH4(g) + H2O(g) CO2(g) + H2(g).

d)Decreasing the total volume of the reaction container: 2 NO2(g) N2O4(g).

e)Increasing the temperature:

CO(g) + 3 H2(g) CH4(g) + H2O(g); H = −230 kJ.

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6.IONIC EQUILIBRIA

6.1.Name and write the formula of the conjugate base of each molecule or ion.

a) HCl; b) HCO3−; c) H2SO4; d) N2H5+.

6.2. Name and write the formula of the conjugate acid of each molecule or ion. a) NO3–; b) OH–; c) H2O; d) HCO3–.

6.3.Identify the conjugate acid-base pairs in each reaction.

a)HS–(aq) + H2O(l) H2S(aq) + OH–;

b)O2–(aq) + H2O(l) → 2 OH–.

6.4.Identify the conjugate acid-base pairs in each reaction.

a)H2S(aq) + NH3(aq) NH4+(aq) + HS–(aq);

b)H2SO4(aq) + H2O(l) → H3O+(aq) + HSO4–(aq).

6.5.Calculate the concentration of hydronium ions in each solution.

a)4.5 mol/L HCl(aq);'

b)30.0 mL of 4.50 mol/L HBr(aq) diluted to 100.0 mL;

c)18.6 mL of 2.60 mol/L HClO4(aq) added to 24.8 mL of 1.92 mol/L NaOH(aq).

6.6. Calculate the concentration of hydroxide ions in each solution.

a)3.1 mol/L KOH(aq);

b)21.0 mL of 3.1 mol/L KOH diluted to 75.0 mL;

c)23.2 mL of 1.58 mol/L HCl(aq) added to 18.9 mL of 3.50 mol/L NaOH(aq).

6.7.Determine whether reacting each pair of solutions results in an acidic solution or a basic solution. Then calculate the concentration of the ion that causes the solution to be acidic or basic. (Assume that the volumes in part (a) are additive. Assume that the volumes in part (b) stay the same.)

a)31.9 mL of 2.75 mol/L HCl(aq) added to 125 mL of 0.0500 mol/L Mg(OH)2(aq);

b)4.87 g of NaOH(s) added to 80.0 mL of 3.50 mol/L HBr(aq).

6.8.2.75 g of MgO(s) is added to 70.0 mL of 2.40 mol/L HNO3(aq). Is the solution that results from the reaction acidic or basic? What is the concentration of the ion that is responsible for the character of the solution?

6.9.Phosphoric acid, H3PO4(aq) is triprotic. It has three hydrogen ions that may be dissociated.

a)Write an equation to show the dissociation of each proton.

b)Show that H2PO4– can act as either an acid or a base.

c)Which is the stronger acid, H3PO4(aq) or H2PO4−(aq)? Explain your answer.

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6.20.At normal body temperature, 37 °C, the value of Kw for water equals 2.5 10–14. Calculate [H3O+] and [OH−] at this temperature. Is pure water at 37 °C acidic, neutral, or basic?

6.21.A sample of baking soda was dissolved in water and the pOH of the solution was

found to be 5.81 at 25 °C. Is the solution acidic, basic, or neutral? Calculate the pH, [H3O+], and [OH−] of the solution.

6.22.A chemist dissolved some Aspirin™ in water. The chemist then measured the pH of the solution and found it to be 2.73 at 25 °C. What are [H3O+] and [OH−] of the solution?

6.23.Calculate the pH of a sample of vinegar that contains 0.83 mol/L acetic acid. What is the percent dissociation of the vinegar?

6.24.In low doses, barbiturates act as sedatives. The formula of barbituric acid is

C4H4N2O3. A chemist prepares a 0.10 mol/L solution of barbituric acid and finds the pH of the solution to be 2.50. What is the acid dissociation constant for barbituric acid? What percent of its molecules dissociate?

6.25.A solution of hydrofluoric acid has a molar concentration of 0.0100 mol/L. What is the pH of this solution?

6.26.Hypochlorous acid, HOCl, is used as a bleach and a germ-killer. A chemist finds that 0.027% of hypochlorous acid molecules are dissociated in a 0.40 mol/L solution of the acid. What is the value of Ka for the acid?

6.27.The word “butter” comes from the Greek butyros. Butanoic acid (common name: butyric acid) gives rancid butter its distinctive odour. Calculate the pH of a 1.0 10–2 M solution of butanoic acid (Ka = 1.51 10–5).

6.28.Caproic acid, C5H11COOH, occurs naturally in coconut and palm oil. It is a weak monoprotic acid, with Ka = 1.3 10–5. A certain aqueous solution of caproic acid has a pH of 2.94. How much acid was dissolved to make 100 mL of this solution?

6.29.Carbonated beverages contain a solution of carbonic acid. Carbonic acid is also important for forming the ions that are present in blood.

CO2(aq) + H2O(l) H2CO3(aq);

H2CO3(aq) + H2O(l) HCO3–(aq) + H3O+(aq);

HCO3–(aq) + H2O(l) CO32–(aq) + H3O+(aq).

Calculate the pH of a solution of 5.0 10–4 mol/L carbonic acid (use Appendix 4). What is [CO32–] in the solution?

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