Chapter 19:
Entropy and Microstates
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Kelsey
Chemistry 178
Verkade
10/28/2010
1. Demo 10/28/2010 = Lycopodium (Fire Breathing) Pumpkin
“Lycopodium powder is a very fine yellow powder made from the spores of Lycopodium
clavatum, also known as stag’s horn club moss and running ground pine. Lycopodium
powder does not readily burn unless it is dispersed as a mist near flame, where it can
ignite because of presence of oxygen to support combustion as well as the increase in
available surface area.”
Further explanation and how to make a Lycopodium Pumpkin (be careful!) may be found
at: http://www.ehow.com/how_6327512_make-lycopodiumpumpkin.html#ixzz13fURJj
ZX
2. The second law of thermodynamics states that there is a direction to the way events occur
in nature. In any spontaneous process the entropy of the universe increases.
Circle the correct answer:
a. For a reversible/irreversible process,
b. For a reversible/irreversible process,
Irreversible processes are spontaneous processes. Entropy is not conserved, for
irreversible processes
is continually increasing (ex. Expanding the
universe increases entropy, you cannot decrease the size of the universe to where
it was before without exerting work).
3. Arrange solid, liquid, and gas in order of decreasing entropy. Explain your choice.
, this is because molecules become more ordered and move less as
you move from gas to liquid to solid. The more ordered a molecule is, the lower the
entropy.
4. (Problem 19.42 in BLBM textbook) Predict the sign of
for each of the following
processes:
a. Gaseous Ar is liquefied at 80 K Negative, moles of gas decrease
b. Gaseous N2O4 dissociates to form gaseous NO2 Positive, moles of gas increase
c. Solid potassium reacts with gaseous O2 to form solid potassium superoxide, KO2
Negative, moles of gas decrease
d. Lead bromide precipitates upon mixing Pb(NO3)2(aq) and KBr(aq) Negative, less
motional freedom, fewer moles of ions in aqueous solution
Supplemental Instruction
1060 Hixson-Lied Student Success Center  294-6624  www.si.iastate.edu
5. What is a microstate and (Problem 19.29 in BLBM textbook) how would each of the
following changes affect the number of microstates available to a system:
a. Increase in temperature
The higher the temperature, the broader the distribution of molecular speeds and
kinetic energies available to the particles. At higher temperature, the wider range
of accessible kinetic energies leads to more microstates for the system.
b. Decrease in volume
A decrease in volume reduces the number of possible positions for the particles
and leads to fewer microstates for the system.
c. Change of state from liquid to gas
Going from liquid to gas, particles have greater translational motion, which
increases the number of positions available to the particles and the number of
microstates for the system.
Microstate: The state of a system at a particular instant; one of many possible
energetically ways to arrange the components of a system to achieve a particular state.
6. Entropy is a measure of how many microstates are associated with a particular
macroscopic state. The Boltzmann equation is:
. What does each variable
stand for?
S = Entropy
k=Boltzmann’s constant (1.38 x 10-23 J/K)
W=number of microstates
7. The third law of thermodynamics states that the entropy of a perfect pure crystal at 0 K is
zero (state of perfect order).
Name the three atomic modes of motion, and what these types of motion do.
Translational: The moving of a molecule from one point in space to another.
Vibrational: The shortening and lengthening of bonds, including the change in bond
angles.
Rotational: The spinning of a molecule about some axis.
Illustrate these three kinds of motion with sketches for the HCl molecule.
Look at page 810 of BLBM textbook, water molecule atomic motion.