Sample Exam #2

CHM2045 Sample Exam #2

Name ______________________________ SS# _________________________ Section _________

Instructions: Put your name, social security number, and section number on the top of this exam page. Answer the following five (5) parts in the notation and conventions of the lecture for a total of 100 points. Read the entire exam and place all answers on this exam sheet. Work alone and consult no one, living or dead, about this test (except Brucat) until after you leave the room. No scrap work will be collected. Notebooks, textbooks and any other study material are not allowed in the exam room. You may use only your writing and calculating instruments; sharing of calculators is NOT allowed. Show proper units and proper significant figures to receive credit. Your name on this exam states the assertion:
I hereby pledge that I have neither given nor received any unauthorized aid on this exam.

h = 6.626 x 10^-34 Js ; c = 2.998 x 10⁸ m/s ; R_H = 2.179 x 10^-18 J; E_n = -Z² R_H / n²;

Part I (5 points each for a total of 20 points)

What is the wavelength in vacuum of radio signals from the Rock 104 radio station (104 MHz)?
How many radial nodes does a 4p orbital have?
Write the electronic configuration of the ground state of the neutral Potassium Atom (Z=19):
Draw a 3d orbital:

Part II (20 points) What is the vacuum wavelength of the photon emitted from a Hydrogen atom that starts from a 3d orbital and ends up in a 2p orbital?

Part III (10 points each for a total of 20 points) Consider our simple theories of Chemical Bonding
a)Draw the Lewis and VSEPR Structures of PCl₅
Be sure to label bond angles

b) Draw the highest occupied molecular orbital in N₂

Part IV (20 points) Using the following average bond dissociation energies,

Bond Average Bond Energy (kJ/mol) Bond Average Bond Energy (kJ/mol) Bond Average Bond Energy (kJ/mol)

C-O 358 C-C 348 H-H 436

C=O 799 C=C 614 C-H 413

C=O 1072 C=C 839 O-H 463

Estimate the enthalpy change for the hydrogenation of ethylene, i.e

C₂H_{4 (gas)} + H_{2 (gas)} = C₂H_{6 (gas)} DH = _____________ kJ/mol
(Hint: Write Lewis Structures)

Part V (10 points each for a total of 20 points) Consider an Elemental Crystal.
a) Draw the Unit Cell of a face centered cubic (fcc) elemental solid

b) What is the number of atoms per unit cell in a face centered cubic (fcc) structure?

Bond	Average Bond Energy (kJ/mol)	Bond	Average Bond Energy (kJ/mol)	Bond	Average Bond Energy (kJ/mol)
C-O	358	C-C	348	H-H	436
C=O	799	C=C	614	C-H	413
C=O	1072	C=C	839	O-H	463