KEY Exam4 1311 F12 v A - full-length exam with answer keys and grading method for each question. Version PDF

Preview

Summary

full-length exam with answer keys and grading method for each question. Version A F12...

Description

CHEM 1311: General Chemistry 1, Fall 2012 Exam #4, December 8, 2012 Class section: Instructor

Section #

Class time

Qin

001

9:00 am to 9:50 am

Gavva

002

10:00 am to 10:50 am

Dieckmann

003

11:00 am to 11:50 am

Sra

004

1:00 pm to 1:50 pm

EXAM TYPE: A _________________________________________________________________________________ Scantron Use In general: 1. For this exam, you are allowed to use a non-programmable and non-graphing calculator that you bring to your desk. You MAY NOT borrow another person’s calculator. You MAY NOT use your cell phone, PDA, or other non-calculator device as a calculator. 2. use #2 pencil ONLY to fill out Scantron sheet, not a pen or marker 3. when filling in bubble on the scantron, be sure to fill in bubble completely, and only one bubble for each entry; pay attention to line numbers on the scantron so that you put the answer in the correct spot 4. when you first get the exam, check to make sure you have all pages of the exam and one periodic table. You should also have one scantron sheet. If you don’t have any of these, contact us immediately. 5. we will announce periodically how much time has elapsed/are left 6. if you have a question, ask (if taking the exam at disability services, let your assistant know and they can call immediately to get an answer to your question) FILLING IN SCANTRON PERSONAL INFO: Bubble info: 1. I.D. NUMBER:

4-digit exam number (left justified)

2. NAME:

LAST NAME

3. TEST FORM:

exam type (A, B, C or D)

4. SUBJECT SCORE:

your section number: (see above for list)

Vertical lines: 1. NAME: GOOD LUCK!

“Exam 4”

space

FIRST NAME

space

MI (left justified)

CHEM 1311: Exam #4

1. The reaction

December 8, 2012

4 Al(s) + 3 O2(g) → 2 Al2O3(s)

Page 2 of 9

ΔH° = –3351 kJ

is _____________, and therefore heat is ____________ by the reaction. A. endothermic, released B. endothermic, absorbed C. exothermic, released D. exothermic, absorbed E. thermoneutral, neither released nor absorbed __________________________________________________________________________________ 2. A sample of copper absorbs 43.6 kJ of heat, resulting in a temperature rise of 75.0 °C. Determine the mass (in kg) of the copper sample if the specific heat of copper is 0.385 J g–1 °C–1. A. 1.51 kg B. 6.62 kg C. 1.26 kg D. 7.94 kg E. 3.64 kg __________________________________________________________________________________ 3. Which of the following gases has the highest average velocity at 400 K? A. CO2 B. N2O4 C. SF6 D. UF6 __________________________________________________________________________________ 4. Coal gasification can be represented by the equation: 2 C(s) + 2 H2O(g) → CH4(g) + CO2(g)

ΔHrxn = ?

Use the following information to find ΔHrxn for the reaction above: CO(g) + H2(g) → C(s) + H2O(g) CO(g) + H2O(g) → CO2(g) + H2(g) CO(g) + 3 H2(g) → CH4(g) + H2O(g)

ΔHrxn = –131 kJ ΔHrxn = –41 kJ ΔHrxn = –206 kJ

A. 15 kJ B. 116 kJ C. –116 kJ D. –372 kJ E. +372 kJ __________________________________________________________________________________ 5. The density of __________ is 0.900 g L–1 at STP. A. CH4 B. Ne C. CO D. N2 E. NO __________________________________________________________________________________ 6. Given that ΔH° = –311 kJ for the hydrogenation of acetylene (C2H2): H–C

C–H (g) + 2 H2(g) → H3C–CH3 (g)

and the following bond energies, determine the value for the C

C bond energy:

Bond energies (kJ mol–1) C–C

350.

C–H

410.

H–H

436

A. 1050 kJ mol–1 B. 833 kJ mol–1 C. 807 kJ mol–1 –1 –1 D. 397 kJ mol E. 595 kJ mol __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 3 of 9

7. How many liters of oxygen are needed to exactly react with 27.8 g of methane (molar mass = 16.042 g mol–1) at STP? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) A. 19.5 L B. 39.0 L C. 77.6 L D. 85.0 L __________________________________________________________________________________ 8. Which one of the following substances will have hydrogen bonding as one of its intermolecular forces?

A.

B.

C.

D. E. __________________________________________________________________________________ 9. How much heat is absorbed/released when 20.00 g of NH3(g) (17.034 g mol–1) reacts in the presence of excess O2(g) to produce NO(g) and H2O(l) according to the following chemical equation? 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l)

ΔH° = 1168 kJ

A. 342.9 kJ of heat are absorbed B. 342.9 kJ of heat are released C. 1372 kJ of heat are absorbed D. 1372 kJ of heat are released E. 247.5 kJ of heat are absorbed __________________________________________________________________________________ 10. Use the information provided to determine ΔH°rxn for the following reaction: CH4(g) + 3 Cl2(g) → CHCl3(l) + 3 HCl(g)

ΔH°rxn = ? –1

compound ΔH°f (kJ mol ) CH4(g) –75 CHCl3(l) –134 HCl(g) –92 A. –151 kJ B. –335 kJ C. 662 kJ D. 117 kJ E. –217 kJ _________________________________________________________________________________ 11. A sample of 0.300 mol of nitrogen occupies 0.600 L. Under the same conditions (constant temperature and pressure), how many moles will occupy 1.200 L? A. 0.600 mol B. 1.50 mol C. 0.33 mol D. 6.00 mol E. 0.150 mol __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 4 of 9

12. An ideal gas differs from a real gas in that the molecules of an ideal gas: A. have no attractive or repulsive interactions between each other B. have appreciable molecular volumes C. have a molar mass of zero D. have no kinetic energy E. have an average molecular mass _________________________________________________________________________________ 13. A piece of iron (mass = 25.0 g) at 398 K is placed in a styrofoam coffee cup containing 25.0 g of water at 298 K. Assuming that no heat is lost to the cup or the surroundings, what will the final temperature of the water be (specific heat of iron = 0.449 J g–1 K–1; specific heat of water = 4.184 J g–1 K–1)? A. 348 K B. 308 K C. 287 K D. 325 K E. 388 K __________________________________________________________________________________ 14. A mixture of CO2 and an unknown gas was allowed to effuse from a container. The CO2 effused 1.25 times slower than the unknown gas. Which of the following could be the unknown gas? A. Ne B. NO C. CO D. Cl2 E. NH3 __________________________________________________________________________________ 15. A 0.465 g sample of an unknown compound occupies 245 mL at 298 K and 1.22 atm. What is the molar mass of the unknown compound? A. 26.3 g mol–1 B. 33.9 g mol–1 C. 12.2 g mol–1 –1 –1 D. 38.0 g mol E. 81.8 g mol __________________________________________________________________________________ 16. Which of the following substances (with specific heat provided) would show the greatest temperature change upon absorbing 100.0 J of heat? A. 10.0 g Ag, s = 0.235 J g–1 °C–1 B. 10.0 g H2O, s = 4.18 J g–1 °C–1 –1 –1 C. 10.0 g ethanol, s = 2.42 J g °C D. 10.0 g Fe, s = 0.449 J g–1 °C–1 –1 –1 E. 10.0 g Au, s = 0.128 J g °C __________________________________________________________________________________ 17. According to kinetic molecular theory, the pressure of a gas in a container will decrease if: A. the number of collisions with the container walls increases B. the number of moles of gas increases C. the temperature of the gas decreases D. the volume of the container decreases __________________________________________________________________________________ 18. A mixture of 0.220 moles CO, 0.350 moles H2 and 0.640 moles He has a total pressure of 2.95 atm. What is the pressure of CO? A. 1.86 atm B. 0.649 atm C. 0.536 atm D. 1.54 atm E. 0.955 atm __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 5 of 9

19. A 1.50 g sample of NH4NO3 (molar mass = 80.052 g mol–1) is added to 35.0 g of water in a coffee cup calorimeter and stirred until it dissolves. The temperature of the water changes from 22.7 °C to 19.4 °C during this solution process. Determine the heat of solution of NH4NO3 (expressed in kJ per mol NH4NO3): NH4NO3(s) → NH4NO3(aq) ΔH = ? A. 25.8 kJ per mol NH4NO3 B. –483 kJ per mol NH4NO3 C. 0.483 kJ per mol NH4NO3 D. –25.8 kJ per mol NH4NO3 E. 483 kJ per mol NH4NO3 __________________________________________________________________________________ 20. An approximation for the value of absolute zero was made from an extrapolation of a plot of what? A. P vs. 1/V B. V vs. T C. n vs. V D. V vs. 1/T E. P vs. n __________________________________________________________________________________ 21. Given: 4 NO2(g) + O2(g) → 2 N2O5(g) ΔH° = –110.2 kJ find ΔH° for :

N2O5(g) → 2 NO2(g) + ½ O2(g)

A. –220.4 kJ B. –55.1 kJ C. 55.1 kJ D. 220.4 kJ E. 110.2 kJ __________________________________________________________________________________ 22. What volume (in mL) will a fixed amount of F2 gas occupy in a syringe at 5.5 atm, if the F2 has a volume of 25.0 mL at 1.2 atm? A. 11 mL B. 17 mL C. 3.8 mL D. 5.5 mL E. 7.6 mL __________________________________________________________________________________ 23. A sample of a gas is at a pressure of 1.35 atm, a temperature of 205.1 K and has a volume of 23.8 L; what will be the final volume of the gas if the pressure changes to 2.84 atm and the temperature rises to 233.4 K? A. 9.9 L B. 44.0 L C. 12.9 L D. 57.0 L E. 0.18 L __________________________________________________________________________________ 24. Which substance in each of the following pairs is expected to have the larger dispersion forces?

A. Br2 in set I and n-butane in set II B. Br2 in set I and isobutane in set II C. I2 in set I and n-butane in set II D. I2 in set I and isobutane in set II __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 6 of 9

25. A mixture of Xe, Kr, and Ar has a total pressure of 6.70 atm. What is the mole fraction of Kr if the partial pressures of Xe and Ar are 1.60 atm and 2.80 atm, respectively. A. 0.343 B. 0.174 C. 0.256 D. 0.481 E. 0.570 __________________________________________________________________________________ 26. Ethyl alcohol (C2H5OH) is produced by the fermentation of glucose (C6H12O6): C6H12O6(l) → 2 C2H5OH(l) + 2 CO2(g)

ΔH° =

–82 kJ

–1

Given that the standard enthalpy of formation is –277.7 kJ mol for C2H5OH(l) and –393.5 kJ mol–1 for CO2(g), find the standard enthalpy of formation for glucose. A. –1424 kJ mol–1 B. –1260 kJ mol–1 C. –753 kJ mol–1 D. –671 kJ mol–1 E. 82 kJ mol–1 __________________________________________________________________________________ 27. The standard enthalpy of formation of NH4Cl(s) is –315.4 kJ mol–1. The equation that describes this formation reaction is: A. NH4+(aq) + Cl–(aq) → NH4Cl(s) B. ½ N2(g) + 2 H2(g) + ½ Cl2(g) → NH4Cl(s) C. N2(g) + H 2(g) + Cl2(g) → 2 NH4Cl(s) D. ½ N2(g) + ½ Cl2(g) + ½ H2(g) → NH4Cl(s) E. N2(g) + Cl2(g) + 4 H2(g) → 2 NH4Cl(s) __________________________________________________________________________________ 28. A pressure of 0.25 atm corresponds to a pressure of __________ mmHg? A. 3.29 x 10–4 mmHg B. 3.04 x 103 mmHg C. 760 mmHg D. 190 mmHg E. 101 mmHg __________________________________________________________________________________ 29. What volume would be occupied by 4.8 g of O2 gas at 0.50 atm and 133 °C? A. 19 L B. 13 L C. 10 L D. 6.7 L E. 3.3 L __________________________________________________________________________________ 30. A 21.8 g sample of ethanol (C2H5OH; molar mass = 46.07 g mol–1) is burned in a bomb calorimeter, according to the following reaction: C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(g)

ΔH°rxn = –1235 kJ

If the temperature rises from 25.0 to 62.3 °C, determine the heat capacity of the calorimeter. A. 4.99 kJ °C–1 B. 15.7 kJ °C–1 C. 5.65 kJ °C–1 D. 63.7 kJ °C–1 –1 E. 33.1 kJ °C __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 7 of 9

31. The following reaction is used to generate hydrogen gas in the laboratory. Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g) If 243 mL of gas is collected at 25 °C and has a total pressure of 745 mm Hg, what mass of hydrogen is produced? A possibly useful table of water vapor pressures is provided below. T (°C) P (mmHg) 20. 17.55 25. 23.78 30. 31.86 A. 0.0226 g B. 0.0717 g C. 0.0190 g D. 0.0144 g E. 0.0449 g __________________________________________________________________________________

CHEM 1311: Exam #4

December 8, 2012

Page 8 of 9

CHEM 1311: Exam #4

December 8, 2012

Page 9 of 9

Potentially Useful Information Avogadro’s Number:

NA = 6.022 x 1023

Rydberg Equation constant (for Hydrogen):

RH = 109,678 cm–1

Constant for Bohr model of H atom:

b = 2.18 x 10–18 J

Speed of light:

c = 2.998 x 108 m s–1

Planck’s constant:

h = 6.63 x 10–34 J s

1 J = 1 kg m2 s–2 mass (me) = 9.1093897 x 10–28 g mass = 1.673 x 10–24 g mass = 1.675 x 10–24 g

electron: proton: neutron:

1 amu (u) = 1.66054 x 10–24 g 1 calorie = 4.184 J 1 Newton (N) = 1 kg m s–2 1 Pa = 1 N m–2 = 1 kg m–1 s–2 1 atm

= = = = =

760 mm Hg 760 torr 101,325 Pa 1.01325 bar 14.7 psi (pounds per sq. in)

R = 0.08206 L atm mol–1 K–1 = 8.314 J mol–1 K–1 Specific heat of H2O(l) = 4.184 J g–1 °C–1

charge (e) = –1.60 x 10–19 C...