Exam 2-A Spring 2020 Answers - SDSU Chem 200/202

CHEM 200/202 Spring 2020 Exam 2-A March 14, 2020

CHEM _______ Lab Section Number: _____

Name (printed):_____________________________________________

Signature:______________________________________

This exam consists of 36 questions all of equal value for a total of 225 points. Make sure that your test has all of the pages. Please read each problem carefully. There are no intentionally misleading questions; each problem should be taken at its face value. Please mark your answers on the Scantron sheet provided to you and on the actual exam.

You will be given a periodic table and an exam information sheet to use during the exam. You may remove it from the exam make it more accessible. You may also use the designated Casio fx-300ms-plus calculator or equivalent non-programmable non-graphing scientific calculator during the exam. Use the back pages of the test as scratch paper. You are not allowed to use any devices capable of accessing the internet, textbooks, notes, or homemade reference sheets during the exam.

You may leave if you finish the exam early. Give the exam and the information sheet to your TA and leave quietly without disturbing other students. Before leaving, check that all your answers have been properly entered on the Scantron sheet and the exam and that your name is written on every page of the exam and on the Scantron sheet.

All cell phones and electronic devices must be turned off and put away. Please remove all hats and caps. Place your books and all papers out of sight under your seat. If the TA believes that you might be looking at your neighbor’s paper, you will be asked to move to a new location.

Exam scores will be posted on Blackboard as soon as the grading is complete. Your test will be returned to you in the first lab meeting of next week. If you have any questions regarding the grading of your exam, please notify your TA.

The time available for the exam is 120 minutes. Good luck!

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Name: ___________________________________________ Lab Section #: _______

Please mark your answers on the scantron sheet using a #2 pencil and also mark your answers on the exam itself.

Mark the test from version “A” on your scantron.

1. A system that undergoes an internal energy decrease of 80 J and at the same time has 50 J of work done on it. What is the heat change of the system?

(a) 130 J(b) —130 J (c) 30 J(d) —30 J (e) 0 J

2. All of the following chemicals have a standard heat of formation of zero at 25°C and 1.0 atm except

(a) N2(g)(b) Fe(l)(c) K(s)(d) F2(g)(e) H2(g)

3. Which statement is incorrect?

(a) No work is done in a reaction occurring in a bomb calorimeter(b) For constant pressure, ∆U = q + w(c) For an endothermic process, ∆H is negative (d) If the work done by the system is greater than the heat absorbed by the system, ∆U

is negative (e) ∆H, in some situations, is equal to the ∆U

4. A student heats 68.63 g of zinc to 98.65 °C and then drops it into a cup containing 98.15 g of

water at 21.84 °C. She measures the final temperature to be 27.02 °C. The heat capacity of the calorimeter was determined to be 1.72 J/°C. Assuming no heat losses, and that the specific heat (capacity) of water is 4.18 J/(g•°C), what is the specific heat capacity of the zinc in J/g°•C?

(a) 0.258 J/g•°C(b) 0.377 J/g•°C(c) 0.434 J/g•°C(d) 0.585 J/g•°C(e) None of these choices is correct.

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5. Which statement is correct?

(a) ΔH values indicate the amount of heat associated with a reaction and is not related to the physical state of the reactants or products.

(b) U, P, V and w are all work functions (c) The enthalpy of combustion is the enthalpy change when one mole of substance is

formed in a combustion reaction.(d) The standard enthalpy of formation is the enthalpy change associated with the

formation of one mole substance from its free elements in their stable forms at standard state conditions.

(e) None of the above statements are correct 6. Which one of the following equations represents the formation reaction of cysteine,

C3H7NO2S(s)?

(a) S(s) + 3C(graphite)+ 7/2H2(g) + O2(g) +N(g) → C3H7NO2S(s)(b) S(s) + 3C(graphite)+ 7/2H2(g) + O2(g) +1/2N2(g) → C3H7NO2S(s)(c) 2S(s) + 6C(graphite)+ 7H2(g) + 2O2(g) +N2(g) → 2C3H7NO2S(s)(d) S8(s) + 3C(graphite)+ 7/2H2(g) + O2(g) +1/2N2(g) → C3H7NO2S(s)(e) 1/8S8(s) + 3C(graphite)+ 7/2H2(g) + O2(g) +1/2N2(g) → C3H7NO2S(s)

7. The enthalpy change for the following reaction is 180.5 kJ

2NO(g) → N2(g) + O2(g)

What is the standard enthalpy of formation, ∆Hf , for NO(g)?

(a) —180.5 kJ(b) 90.25 kJ(c) —90.25 kJ(d) 234.6 kJ(e) none of the above is right

8. Which one of the following equations represents the formation reaction for CH3HgCl?

(a) 2Hg(l) + 2C(graphite) + 3H2(g)+Cl2(g)→ 2CH3HgCl(s)(b) Hg(l) + C(graphite) + Cl(g) + 3/2H2(g)→ CH3HgCl(s)(c) Hg(l) + C(graphite) + HCl(g) + H2(g)→ CH3HgCl(s)(d) Hg(l) + C(graphite) + 1/2Cl2(g) + 3/2H2(g)→ CH3HgCl(s)(e) Hg(l) + C(diamond) + HCl(g) + H2(g)→ CH3HgCl(s)

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9. When 1.42 g of iron reacts with 1.80 g of chlorine, the reaction results in the production of FeCl2 along with 8.60 kJ of heat. Determine the enthalpy change for a reaction that forms one mole of iron chloride.

(a) —336 kJ(b) —339 kJ(c) —342 kJ(d) —355 kJ(e) —362 kJ

10. An aluminum children’s toy at 140.°C has exactly three times the mass of another aluminum toy, which is at 50.°C. Both toys are placed inside a calorimeter whose heat capacity is negligible. What is the final temperature inside the calorimeter? caluminum = 0.900 J/g•°C

(a) 92 °C (b) 157 °C (c) 64 °C (d) 118 °C(e) 123 °C

11. A scientist measures the standard enthalpy change for the following reaction to be —209.0 kJ:

CO(g) + 3H2(g) → CH4 (g) + H2O (g)

Based on this value and the standard ∆Hf of the following substances what is the standard enthalpy of formation of CH4?

(a) —33.7 kJ/mol(b) —78.0 kJ/mol(c) —77.0 kJ/mol(d) —561.0 kJ/mol(e) 340.0 kJ/mol

12. How much heat will be produced from the combustion of 2.500 L of isooctane, (C8H18)? The density of isooctane is 0.692 g/mL and its ∆Hc= —5461 kJ/mol

(a) —8.271 x 101 kJ(b) —8.271 x 104 kJ(c) —7.854 x 104 kJ(d) —9.448 x 106 kJ(e) —4.135 x 101 kJ

Compound H2O (g) H2O (l) CO(g)

∆Hf o (kJ/mol) —241.5 —285.8 —110.5

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13. Given the following information, calculate the enthalpy of this reaction

2C(graphite) + H2(g) → C2H2(g) ΔH = ?

(1) C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(l) ΔHo = —1299 kJ

(2) C(graphite) + O2(g) → CO2(g) ΔHo = —393.5 kJ

(3) 1/2O2(g) + H2(g) → H2O(l) ΔHo = —285.8

(a) 512 kJ(b)1014 kJ(c) 226 kJ(d) —512 kJ (e) —227 kJ

14. Which of the following is not a state function?

(a) Enthalpy(b) Work (c) Pressure (d) Volume(e) Internal Energy

15. In the lab a student burns a 0.509 g sample of 9,10-anthracenedione (C14H8O2) in a bomb calorimeter containing 1050.g of water. The temperature increases from 25.20°C to 28.20 °C. The heat capacity of water is 4.184 J/g°C. The molar heat of combustion is —6464 kJ per mole of 9,10-anthracencedione. Calculate the heat capacity of the calorimeter.

C14H8O2(s) + 15O2(g)→ 14CO2(g) + 4H2O(l)

(a) 439 J/°C(b) 478 J/ °C(c) 527 J/ °C(d) 874 J/ °C(e) 954 J/ °C

16. A piece of unknown substance weighs 44.7 g and requires 2110. J to increase its temperature from 23.2 °C to 89.6 °C. What is the specific heat of the substance?

(a) 3.19 J/g•°C(b) 0.711 J/g•°C(c) 0.0711 J/g•°C(d) 0.319 J/g•°C(e) 0.452 J/g•°C

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17. A system that undergoes an adiabatic change (i.e., q = 0) and has work done on it has:

(a) w < 0, ∆E < 0(b) w > 0, ∆E > 0(c) w > 0, ∆E < 0(d) w < 0, ∆E > 0(e) w > ∆E

18. Benzene is a starting material in the synthesis of nylon fibers and polystyrene (styrofoam). Its specific heat capacity is 1.74 J/(g•K). If 16.7 kJ of energy is absorbed by a 280. g sample of benzene at 23.0°C, what is its final temperature?

(a) —22.3 °C(b) 36.3 °C(c) 11.3 °C(d) 57.3 °C(e) None of the above answers is correct

19. Of the symbols below, which is used to express wavelength?

(a) 𝓥(b) 𝛌(c) P(d) h(e) π

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Below are the graphical representations of five (numbered) waves. Use those images to answer the following two questions.

20. Which of the waves in the figure above has the shortest wavelength?

(a) Wave 1(b) Wave 2(c) Wave 3(d) Wave 4(e) Wave 5

21. Which of the waves in the figure above has the lowest energy?

(a) Wave 1(b) Wave 2(c) Wave 3(d) Wave 4(e) Wave 5

22. The frequency used by devices communicating via Bluetooth® is 2.4MHz. What is the energy of radio waves with this frequency?

(a) 1.2 × 10–22 J(b) 1.6 × 10–27 J(c) 1.6 × 10–22 J(d) 8.3 × 10–17 J(e) 1.2 × 10–35 J

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1 2 3

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23. Which statement below best describes what was observed for the Photoelectric Effect?

(a) That if a wavelength of light had sufficiently high frequency, under the right conditions, it could eject an electron from a piece of metal.

(b) That despite predictions from classical mechanics and electromagnetism, radiation from heated objects had a peak intensity before the intensity decreased at shorter wavelengths.

(c) That the emission of light from an excited gas at low pressure results in an emission spectra with a few bright emission lines, and mainly black regions with no emissions.

(d) That the orbits of electrons around the nucleus of an atom were in quantized energy levels, and that the electron was moving in these orbits as a standing wave.

(e) That firing a stream of electrons at two very closely spaced slits, or at a thin sheet of atoms, will result in a diffraction pattern similar to that seen with light.

24. A hydrogen atom is excited such that its electron is in the n=5 energy level. The electron relaxes down to the n=3 quantum level, releasing a photon in the process. What is the frequency of the photon being released?

(a) 1.09 × 1015 Hz(b) 2.34 × 1014 Hz(c) 7.31 × 1014 Hz(d) 1.55 × 10–19 Hz(e) 2.56 × 1015 Hz

25. The electron on a hydrogen atom has gained enough energy to be in the n=5 energy level. Over time the electron releases that energy, by sequentially moving the each of the lower (n= 4, 3, 2, and 1) energy levels, releasing a photon of light with each energy level change. During which of those transitions does the emitted photon have the shortest wavelength?

(a) From n = 5 to n = 4.(b) From n = 4 to n = 3.(c) From n = 3 to n = 2.(d) From n = 2 to n = 1.(e) The photons all have the same energy.

26. An atom of He+ has its electron in the n = 3 energy level. The atom is struck by a photon with an energy of 7.27×10–19 J, exciting the electron to a higher energy level. What level has the electron been excited to?

(a) 2(b) 4(c) 5(d) 6(e) 7

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27. What is the energy of an electron on a Li2+ in an orbit with n = 5?

(a) –7.85 × 10–19 J(b) –3.49 × 10–19 J(c) –1.31 × 10–18 J(d) –4.36 × 10–19 J(e) –2.18 × 10–18 J

28. The CERN Large Hadron collider is a 27 km long ring that is used to accelerate subatomic particles to very high velocities in order to collide them with other particles in experiments investigating the fundamentals of matter. If the collider is used to accelerate proton (1.67×10–24 g) to 99% the speed of light (± 2.4×106 m/s), what is the uncertainty of the position of the proton in the 27 km loop?

(a) 1.9 × 10–29 m(b) 1.3 × 10–14 m(c) 1.2 × 10–11 m(d) 1.3 × 10–17 m(e) 1.9 × 10–19 m

29. Which is not a valid quantum number for a ground state electron on an atom of germanium?

(a) n = 2 , l = 1 , ml = 0 , ms = +½ (b) n = 4 , l = 1 , ml = –1 , ms = +½(c) n = 4 , l = 3 , ml = –2 , ms = –½(d) n = 3 , l = 2 , ml = 1 , ms = –½(e) n = 3 , l = 0 , ml = 0 , ms = +½

30. How many nodes are there in a 4s orbital?

(a) 1(b) 2(c) 3(d) 4(e) 5

31. Of the ions listed below, which is the smallest?

(a) I—

(b) Cs+

(c) Ba2+

(d) Te2—

(e) None, they are all the same size.

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32. Consider the third ionization energy for each of the atoms listed below. Which of these atoms will have the least third ionization energy?

(a) Mg(b) Na(c) Ca(d) Ne(e) Rb

33. The orbital diagram below represents the outermost electrons of which period five atom?

(a) Ru(b) Ag(c) Mo(d) Fe(e) Pd

34. On an atom of sulfur how many electrons have the quantum numbers which include l = 1 and ms = –½?

(a) 8(b) 2(c) 1(d) 4(e) 5

35. Who’s guidance explains why electrons remain unpaired until each suborbital is filled with a single electron first?

(a) Pauli’s exclusion principle.(b) de Broglie’s effect.(c) Brannigan’s law(d) Hund’s rule.(e) Planck’s principle.

36. Which of the following is not isoelectronic with Ne?

(a) Na+

(b) Mg2+

(c) F–

(d) Li+(e) O2–

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5s 4d 5p


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Exam 2-A Spring 2020 Answers - SDSU Chem 200/202

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