CHEM152. Craig. Winter 2017 . Exam 2 Review Key PDF

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UWCHEM152(CRAIG)

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Exam2ReviewProblems

CHEM152Exam2ReviewProblems 

1.Whatistheconcentrationofsulfateinasaturatedsolutionofbariumsulfate (Ksp=1.5x10‐9)?  A)3.9x10‐5M B)1.5x10‐9M C)2.3x10‐18M D)7.2x10‐4M E)1.9x10‐5M   2.WhatistheconcentrationofPb2+ina0.100MKIsolutionwithsolidPbI2(Ksp=1.4x10‐8)?  A)1.4x10‐6M B)1.4x10‐8M C)1.4x10‐7M D)1.2x10‐4M E)1.2x10‐5M

3. For one mole of crystalline argon (Ar) at 0 K, the entropy is: A) B) C) D) E)

1 –qrxn Hrxn/T 0 –TG

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Exam2ReviewProblems

4. Which of statements A through D is INCORRECT? A) To calculate work, all you need is the initial and final states of the system. B) A monatomic ideal gas has only translational kinetic energy. C) The expression H = nCPT is valid for any state change. D) E = H if there is no volume change in the system under constant pressure conditions. E) Two of statements A through D are incorrect.

5. Which of the following has H of  0 ? A) B) C) D) E)

CO2(g) Br2(s) He(l) Na(s) H2O(g)

6. Which reaction will perform work on the surroundings when conducted at constant pressure and 25oC? A)

B2 H6 (g ) + 3 O 2 ( g )  B 2O3( s) + 3 H 2O( g)

B)

C(s ) + H2O(g )  H 2 (g ) + CO( g ) 2 C8 H18 (l ) + 25 O2 (g )  16 CO2 ( g ) + 18 H 2O(l )

C) D) E)

N 2 ( g ) + 2 O 2 ( g )  2 NO2 (g )

2 ClF3 (g ) + 2 O 2 ( g)  Cl2O( g) + 3 F2O( g)

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Exam2ReviewProblems

Use the following to answer questions 7-8: A 1.5-mol sample of hydrogen (H2) gas, initially in state A, is subjected to a one-step, isothermal expansion to state B. Following this, the gas is subjected to a one-step, isothermal compression back to state A.

7. What is wA B , the work done in the expansion step? A) B) C) D) E)

–40 J –5980 J –4050 J +40 J +4050 J

8. What is S for the overall cycle? A) B) C) D) E)

+54.4 J K–1 +81.6 J K–1 –81.6 J K –1 0 J K–1 –54.4 J K –1

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Exam2ReviewProblems

Use the following to answer questions 9-10: A 3.00-mol sample of a carbon dioxide gas is heated from 8oC to 63oC under a constant pressure of 1.30 atm. The constant-pressure heat capacity for gaseous carbon dioxide is 33.2 J mol–1 K–1.

9. Calculate q. A) B) C) D) E)

+5480 J +3430 J –5480 J +2060 J –3430 J

10. Calculate w. A) B) C) D) E)

+13.5 J +1370 J –13.5 J –1370 J –3.50 104 J

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11. The combustion of methanol (CH3OH) takes place according to the reaction 2 CH3OH(l) + 3 O2(g)  2 CO2(g) + 4 H2O(l) o for the combustion of 1 MOLE of methanol Use the data below to calculate Hrxn under standard conditions.

H o (kJ mol–1)

C(s ) + 2 H 2 (g ) + 1/2 O 2 (g )  CH 3OH(l ) C(s ) + O 2(g )  CO 2( g ) 2 H 2( g) + O 2( g )  2 H 2O( l)

A) B) C) D) E)

–238.5 –393.5 –573.0

+728 kJ/mol –728 kJ/mol +1456 kJ/mol –1456 kJ/mol Not enough information.

12. What volume of NH3(g), measured at 298 K and 1.00 atm, must be burned in excess oxygen to release 1.0  104 kJ of heat to the surroundings? 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O(l) A) B) C) D) E)

∆H = –1400 kJ

7.0  102 L 29 L 7.1  104 L 1.7  102 L 1.8  104 L

13. Which process will result in the largest POSITIVE entropy change in the SURROUNDINGS at constant pressure? A) B) C) D) E)

H2O( g )  H 2O( s) H2O(s )  H 2O(l ) H 2 O( l)  H2 O( g )

H2O(l )  H 2O(s) H2O(s )  H2O( g )

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14. Given the following data, calculate the normal boiling point for formic acid (HCOOH): HCOOH(l)  HCOOH(g)

HCOOH(l) HCOOH(g)

A) B) C) D) E)

S° (J K–1 mol –1) 130. 251

H°f (kJ mol –1) -410. -363

388 K 5687 K 0.00257 K 0.388 K 2.57 K

15. For which of the following is G  0 ? A)

C)

B)

D)

E)

G  0 in each case.

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Exam2ReviewProblems

16. Consider the following isochoric processes conducted on monatomic ideal gases: Process I heating from 25 K to 50 K Process II heating from 100 K to 200 K Process III heating from 500 K to 1000 K Which of the following is true concerning the entropy changes in these systems? A) B) C)

S I > S II > SIII S I = S II = SIII

S I < S II < SIII D) I need to know the volume of each system to answer this question.

o o 17. For the reaction below, H rxn = –43 kJ mol–1 and S rxn = +44 J mol–1 K–1.

HCl(aq )  AgNO3 (aq )  AgCl(s )  HNO 3(aq) Which of the following statements is true regarding the spontaneity of this reaction? A) B) C) D)

It is spontaneous above 980 K. It is non-spontaneous at all temperatures. It is spontaneous below 980 K. It is spontaneous at all temperatures.

18. A gas sample in a cylinder is supplied with 524 kJ of energy as heat. At the same time, a piston compresses the gas, doing 340 kJ of work. What is E for this process? A) B) C) D) E)

+864 kJ +524 kJ –864 kJ –184 kJ +184 kJ

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Exam2ReviewProblems

19. Based on the reaction below, what energy change occurs when 1.6 mol of chlorine reacts in the presence of excess methane (CH4)? CH4 + 4 Cl2(g)  CCl4(g) + 4 HCl(g) A) B) C) D) E)

Hrxn = –434 kJ/mol rxn

1.7  102 kJ is released. 4.3  102 kJ is released. 1.7  102 kJ is absorbed. 6.9  102 kJ is absorbed. 6.9  102 kJ is released.

20. Use the data below to determine the heat of formation ( H of ) for AgI(s). 2 AgI(s) + Br2(g)  2 AgBr(s) + I2(s)

o H rxn = –108.0 kJ

H of for AgBr(s) = –100.4 kJ/mol H of for Br2(g) = +30.9 kJ/mol

A) B) C) D) E)

+77.3 kJ/mol –77.3 kJ/mol –61.8 kJ/mol +61.8 kJ/mol –123.5 kJ/mol

21. Calculate the entropy change when 5.00 mol of a monatomic ideal gas is cooled from 135°C to 85°C at 1 atm. A) B) C) D)

-48.9 J/K -8.15 J/K -250.0 J/K -13.6 J/K

22. A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature decreases from 21.5°C to 20.8°C as the solid dissolves. Which of the following is true for the dissolving of the solid? A) B) C) D)

Suniv > 0 Ssys< 0 Ssurr > 0 H < 0

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23. The dissociation of hydrogen is an endothermic process: H2(g)

2H(g)

This process is... A) B) C) D)

...spontaneous at any temperature. ...spontaneous at low temperature. ...spontaneous at high temperature. ...non-spontaneous at any temperature.

24. The standard enthalpy change for the following reaction is –542 kJ: H2(g) + F2(g)  2HF(g) Calculate the standard enthalpy of formation ( Hof ) of hydrogen fluoride. A) B) C) D) E)

–1084 kJ/mol +542 kJ/mol –542 kJ/mol –271 kJ/mol +271 kJ/mol

25. The reaction Ag+(aq) + Cl-(aq)  AgCl(s) has a negative value of G°. Which of the following statements must be true? A) B) C) D)

The reaction is endothermic. The reaction is fast. The equilibrium lies far to the right. The equilibrium lies far to the left.

26. Based on the reaction below, what energy change occurs when 1.8 mol of chlorine reacts in the presence of excess methane (CH4)? CH4 + 4 Cl2(g)  CCl4(g) + 4 HCl(g) A) B) C) D) E)

Hrxn = –434 kJ/mol rxn

7.8  102 kJ is released. 7.8  102 kJ is absorbed. 2.0  102 kJ is released. 2.0  102 kJ is absorbed. 4.3  102 kJ is released.

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Exam2ReviewProblems

27. Which statement is true of a process in which 1 mol of a gas is expanded from state A to state B? A) When the gas expands from state A to state B, the surroundings are doing work on the system. B) The amount of work done in the process must be the same, regardless of the path. C) It is not possible to have more than one path for a change of state. D) The final volume of the gas will depend on the path taken. E) The amount of heat released in the process will depend on the path taken.

28. For which of the following reaction(s) is the enthalpy change for the reaction not equal to H°f of the product? I. 2H(g)  H2(g) II. H2(g) + O2(g)  H2O2(l) III. H2O(l) + O(g)  H2O2(l) A) B) C) D) E)

I only II only III only I and III II and III

29. One mole of a liquid is vaporized at its boiling point, 65°C and 1.00 atm. Hvap for the liquid is 43.8 kJ/mol at 65° C. Calculate E. A) B) C) D) E)

16.1 kJ 41.0 kJ 46.6 kJ 71.5 kJ none of these

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30. Zinc oxide can be reduced to zinc metal by reacting it with carbon:

2 ZnO(s ) + C(gr )  2 Zn(s ) + CO 2(g ) Using the following thermodynamic data, determine G°rxn for this reaction at 25oC.

ZnO(s) C(gr) Zn(s) CO2(g)

A) B) C) D) E)

H°f (kJ mol–1) -348 data not provided data not provided -393

S° (J mol–1 K–1) 44 6 42 214

G°f (kJ mol–1) data not provided data not provided data not provided -394

+297 kJ/mol +242 kJ/mol +328 kJ/mol –60,500 kJ/mol More information needed.

31. A 25°C, G° = 27.0 kJ mol–1 for the acid dissociation of acetic acid: CH3COOH(aq) + H2O(l)

CH3COO–(aq) + H3O+(aq)

What is G at 25°C for a solution of acetic acid in which the initial concentrations are [CH3COOH]o = 0.10 M [H3O+]o = 2.0  10–8 M [CH3COO–]o = 0.010 M

A) B) C) D) E)

+50. kJ –50. kJ +23 kJ –23 kJ 27 kJ

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Exam2ReviewProblems

32. Consider the following reaction at 25°C, 2N2O5(g)

4NO2(g) + O2(g)

for which H° = 110.0 kJ mol–1, and S° = 453.8 J mol–1 K–1. Which of the following is true for this reaction? A) B) C) D) E)

Reaction is spontaneous at all temperatures. Reaction is non-spontaneous at all temperatures. Reaction in spontaneous at low temperatures. Reaction is spontaneous at high temperatures. The system is at equilibrium at standard conditions and 25oC.

33. If the change in entropy of the surroundings is –337 J/K for a process at 436 K and constant pressure, what is the heat flow absorbed by the SYSTEM? A) B) C) D) E)

+773 kJ +17.7 kJ –147 kJ –17.7 kJ +147 kJ

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34. (15 pts) Calculate the heat of formation ( H of ) of acetlyene (C2H2) gas using the following heats of reaction: o (kJ mol 1 )  Hrxn

2 C2 H2 (g ) + 5 O 2 ( g )  4 CO 2( g) + 2 H 2O( l) C(s ) + O 2 ( g )  CO 2( g ) 2 H2 (g ) + O2 ( g)  2 H 2O( g)

–2600 –394 –572

To receive full credit, you must show how you manipulated each chemical equation above to achieve your target chemical equation, and your resulting manipulations of the o Hrxn values to achieve the H of of C2H2(g). You may ignore significant figures. 226 kJ/mol

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Exam2ReviewProblems

35. (20 pts) Consider the following two-step process carried out on 0.75 mol of a monatomic ideal gas: Step 1 (Isobaric heating): A (4.00 atm, 2.00 L)  B (4.00 atm, 15.00 L) Step 2 (Isochoric cooling): B (4.00 atm, 15.00 L)  C (2.00 atm, 15.00 L) Calculate q, w, H, and E for each step and record your results in joules in the spaces provided. You may ignore significant figures. Step 1: q1 __________ w1 __________ E1 __________ H1 __________

Step 2: q2 __________ w2 __________ E2 __________ H2 __________

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36. (20 pts) For the gas phase reaction 2 NO2 2 NO + O2, H° = 114.0 kJ mol–1 and K = 4.44  10–13 at 25oC. Use this data to calculate S° for the reverse reaction shown below at 25oC. Express your result in J mol–1 K–1. 2 NO + O2

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2 NO2

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37. At 25°C, Ka = 6.2  10–10 for the dissociation of hydrocyanic acid: +

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