CHEM2141
Students:
If you are encountering difficulities with the exam problems please email me and I will respond to the group as in this email. I suggest doing the "easier" problems first (i.e. problems 1 & 4). Please have your lecture notes handy.
I have received several inquires concerning problem 2d, 2e and 3a. So I have provided useful info below:
If you are encountering difficulities with the exam problems please email me and I will respond to the group as in this email. I suggest doing the "easier" problems first (i.e. problems 1 & 4). Please have your lecture notes handy.
I have received several inquires concerning problem 2d, 2e and 3a. So I have provided useful info below:
Problem
2d -
d.
(7 pts) For 
of
part b, if all of the energy was restricted the n30
mode (3026.758 cm-1), what would be the approximate (round
off to nearest integer) value of the corresponding vibrational quantum
number for that mode,
u30.
This
problem is essentially a Harmonic oscillator of fundamental frequency n30
= 3026.758 cm-1. The value of the u qauntum
number (that we call u30
in this case) will be very high. Don't worry about the zero point
energy, because we are concerned with the energy in the highu state
minus the energy at u
= 0 (zero point energy). Thus the zero point energy is an offset.
For
more clarification see the solution to Homework 3 problem
8. Note the (0,3,0) is a state with 3 vibrational quanta for the n2
mode. So in this u
= 3, and the energy in wavenumbers = 3 x n2.
Note: This problem
is not computationally difficult, but it does involve conceptual
understanding of what we mean by a vibrational overtone, and the energy
(above the zero point energy) associated with the vibrational overtone.
Problem
2e -
e.
(5 pts) If the C-H bond energy in benzene is 515.5 kJ mol-1,
determine the maximum energy translational energy
in kJ mol-1 of a H atom ejected from the phenyl
radical following the 193 nm absorption of C6H6 to
form the phenyl radical and H atom. (Hint: similar to photoelectric
effect, except an atom is ejected instead of an electron).
In
the photoelectric effect you have to account for the conservation of
energy with the work function, photon energy & kinetic (translational) energy
of the electron. Similarly in this problem you also have 3 energies to
account for, which obey an energy conservation. Just be sure that you
are dealing with energies per mole, and not energies per molecule. Note
at the top of the exam: 83.6
cm-1
= 1 kJ mol-1
Problem 3a
-
(10
pts) Employ the steady-state approximation for [ClO4] to show
that
i.e.
In lecture we were primarily concerned with simplifying the expression: d[product]/dt, but this problem asks for d[Cl2O6]/dt which has two terms: a production term and a depletion term. To add the two terms, you must make the denominators the same. For exam if you are adding 2/3 to 7. You multiply the numerator and denominator of 7/1 by 3 to get 21/3: 2/3 + 21/3 = 23/3. Utilize a similar approach for problem 3a of the Take Home Final exam.
This problem (3a) along with 3e can be quite tedious, so work slowly and carefully.
Wade Sisk
Associate Professor of Chemistry
The University of North Carolina Charlotte
9201 University City Blvd.
Charlotte, NC 28223-0001
Ph:(704)687-4433, Fax:(704)687-3151
email: wsisk@uncc.edu <mailto:wsisk@uncc.edu>
URL: <http://chemistry.uncc.edu/faculty/sisk/profile_sisk.html>