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Fall, 2004 CHEM 001 Exam III: Multiple Choice, Short Answer, and Problems, Exams of Chemistry

Georgetown University (GU)Chemistry

A chemistry exam from fall, 2004 for chem 001. It includes multiple choice questions, short answer questions, and problems related to various topics such as lewis structures, formal charges, bond energies, and gas properties. The document also provides some useful equations and constants.

Typology: Exams

Pre 2010

Uploaded on 11/08/2009

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Name___________________________________
CHEM 001
Fall, 2004
Hour Exam III
YOU MUST SHOW ALL OF YOUR WORK AND/OR LOGIC ON THIS EXAM
Please read and sign the following statement:
"I have neither given nor received help on this exam."
Signature_______________________________
I. Multiple choice ____________/20
II. Short answer ____________/32
III. Problems ____________/48
TOTAL_____________________
Possibly useful equations and constants:
PV=nRT
M
RT3
u
1
2
2
1
M
M
r
r
nRTnb)(V
V
an
P
2
R = 8.314 J/K-mol = 0.0820 L-atm/K-mol
Vapor pressure of water at 20ºC = 17.5 mm Hg
760 mm Hg = 1 atm
pf3
pf4
pf5
pf8

Partial preview of the text

Download Fall, 2004 CHEM 001 Exam III: Multiple Choice, Short Answer, and Problems and more Exams Chemistry in PDF only on Docsity!

Name___________________________________ CHEM 001 Fall, 2004 Hour Exam III YOU MUST SHOW ALL OF YOUR WORK AND/OR LOGIC ON THIS EXAM Please read and sign the following statement: "I have neither given nor received help on this exam." Signature_______________________________ I. Multiple choice ____________/ II. Short answer ____________/ III. Problems ____________/ TOTAL_____________________ Possibly useful equations and constants: PV=nRT M 3 RT u1 2 2 1 M

M

r r(V nb) nRT V n a P 2  ^        R = 8.314 J/K-mol = 0.0820 L-atm/K-mol Vapor pressure of water at 20ºC = 17.5 mm Hg 760 mm Hg = 1 atm

I. Multiple choice (2 points each) Circle the letter for the correct answer.

  1. As we go from polar covalent to purely covalent bonding, the degree of transfer of charge from one atom to the other a. increases b. decreases c. stays the same d. halves
  2. The Lewis dot symbol for beryllium ion includes: a. the symbol Bl b. 8 electrons c. designation for a zero overall charge d. none of the above
  3. Which of the following follows the octet rule in its compounds: a. Be b. Al c. F d. none of the above
  4. The lattice energy is the a. energy to completely separate a mole of a solid ionic compound into its gaseous ions. b. energy to completely separate a mole of a solid ionic compound into its individual elements in their standard states. c. energy to form a mole of a solid ionic compound from its gaseous ions. d none of the above
  5. In the following Lewis dot structure for CNO─, what is the formal charge on the nitrogen atom?   ┐- : C=N=O: a. + b. 0 c. - d. none of the above
  6. As we go from the top to the bottom of a group in the periodic table, the electronegativity a. increases b. decreases c. stays relatively constant d. goes up and then down

c. Xe F 4 .. .. electron domain: octahedral : F : : F : molecular: square planar Xe : .. .. : F F :

....

  1. Based on formal charges, which of the following structures for phosphate is most likely and why? (8 points) .. .. : O :  3- : O :  3- .. │ .. .. │ .. : O = P - O : : O ─ P ─O : │ ^ ^ │  : O : : O :   The one on the left is the more likely because provides for one of the oxygens and the phosphorus to have formal charges of zero, leaving the others with a -1 formal charge (Since O is very electronegative this is a favorable situation.) The one on the right would mean that all of the oxygens were -1 and the P was +1. Having a + and a - next to one another is not favorable
  2. Rank the following in terms of bond energy (highest to lowest) and justify your answer: (6 pts) C - N C - P C - O C - O > C - N > C-P The bond energy will decrease as we go from N to P due to the greater charge localization between the carbon and the nitrogen (smaller atom, less diffuse p orbital on N as opposed to P). As we go from N to O, the smaller size of the atom means the atoms can have better overlap and the more electronegative means that the electron density is more confined to the area between the atoms, giving a strong bond.
  1. For what properties of gases do the a and b constants in the van der Waals equation correct? Why does it make sense that the term containing a is positive and that containing b negative? (6 pts) a corrects for the attractive forces between atoms, while b corrects for the volume of the atoms or molecules themselves. Attractive forces would tend to decrease the number of collisions/time of the gas atoms or molecules with the container walls, so a correction must be added to the measured pressure. On the other hand, the volume of the atoms or molecules decreases the volume available for them to move about. III. Problems:
  2. Based on bond enthalpies given below, calculate the change in enthalpy for the formation of carbon dioxide and water from gaseous n -butane (shown below) and oxygen gas. (10 pts) Type of bond Bond enthalpy (kJ/mol) C-H 413 C-C 348 H H H H │ │ │ │ H – C – C – C – C - H │ │ │ │ H H H H

b) If the valve is opened so that the gases can diffuse freely between the containers, what will be the final pressures of each gas (assume T does not change)? c) What is the total pressure in the system after the two samples have mixed? d) What is the mole fraction of each gas after the two samples have mixed?

  1. If it takes one liter of helium 50 s to escape from a container, how long would it take for one liter of hydrogen gas to escape at the same temperature and intial pressure? (6 pts)
  1. Five (5.00) g of oxygen is trapped over water at 20oC. The total pressure in the system is 1.01 atm. What volume will the sample occupy? (6 points)