Percy Lavon Julian

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Percy Lavon Julian
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• Percy graduated from State Normal School for
  Negroes in 1916 at the top of his class

He applied and was accepted into DePauw
University, he began as a probationary student,
having to take higher level high school classes
along with his freshman and sophomore
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  In addition to this full course load, he also
worked to support himself. He was a member of the
Phi Beta Kappa Honor Society and graduated as the
Class Valedictorian in 1920. 
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Though at the top of his class, he was
discouraged from seeking graduate school because
of potential racial sentiment by his coworkers
and employers. Instead, he took the position as a
chemistry teacher at Fisk University, a Black
college in Nashville, Tennessee.
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• Later he developed his own company and created
  the drug physostigmine, a drug which was used as
  a treatment for glaucoma.
• After much work and adversity, Julian was
  successful and became internationally hailed for
  his achievement.

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Percy Lavon Julian

• aero-foam which worked as a flame retardant and
  was used by the United States Navy and saved the
  lives of countless sailors during World War II.

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• developed a way to inexpensively develop male
  and female hormones from soy beans.
• These hormones would help to prevent
  miscarriages in pregnant women and would be used
  to fight cancer

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• So significant was his work that Percy Lavon
  Julian in 1950 the City of Chicago named him
  Chicagoan of the Year.

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• After purchased a home for his family in nearby
  Oak Park, the home was set afire by an arsonist
  on Thanksgiving day 1950.
• A year later, dynamite was thrown from a passing
  car and exploded outside the bedroom window of
  Percy's children.

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• When chemist Percy Lavon Julian, received an
  honor scroll from the American Institute of
  Chemists, he quoted Henry Wadsworth Longfellow
  which begins Where should the scholar live? In
  solitude or in society?
• Dr. Julian's answer was in society.
• "My prime concern, is that the scientist
  recognize the magnitude of responsibility resting
  upon his shoulders, when the nation entrusts so
  much of its wealth in his hands."

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It is all about tolerancefreedom of
religionfreedom of speechfreedom to meet
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Go over test results

• Retake of exam

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Last lecture we discussed the suttle kinds of
bonds that develop intermolecularly
When the electron is pulled off a hydrogen by a
electronegative Oxygen or Nitrogen Forces that
come from permanent negative and positive regions
of a molecule ie sugar Transient Shifting
negative and positive regions that occur around a
nonpolar compounds or elements only at cold
temperatures and high pressures

• Hydrogen bonds
• Dipole dipole
• London dispersion forces

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One clarification

• I can see how one molecule can undergo London
  forces by having the electron cloud shift
  momentarily but how could a entire block of CO2
  collectively become solid with London forces?

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Induced London dispersion forces
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As we create or break these bonds with the
addition or removal of energy the molecules
change state
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A vapor is the gas of any compound that would
normally be found as a liquid at room temperature
and pressure. For example, water, gasoline,
rubbing alcohol

• http//www.chem.uidaho.edu/honors/vapress.html

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vapor pressure barometer
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At a given temperature only a percentage of the
molecules will have enough energy to break the
intermolecular bonds an break free of the bulk
liquid
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The stronger the bonds between molecules the
fewer molecules can escape
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The higher the energy the more energy available
to break bonds
Loss of compounds or atoms from a liquid to a gas
is called Vaporization or evaporation

• Low temp High temp

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If the container is open the liquid will
eventually completely evaporate
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On the other hand
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movement of atoms or compounds from a gas to a
liquid is condensation
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A molecule or atom that collides with a liquid
will usually condense into the body of the
liquid.

• The more molecules or atoms that collide with the
  liquid the more condensation occurs

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If the rate of vaporization equals the rate of
condensation then the system is said to be in
equilibrium

• A closed container of alcohol reaches equilibrium
  when the rate of vaporization equals the rate of
  condensation this is a dynamic equilibrium

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Equilibrium
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The vapor pressure is a measure of the force
exerted by a gas during vaporization

• The hotter the solution, the greater the vapor
  pressure

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At a particular temperature a liquid vapor two
phase system will generate a constant vapor
pressure at equilibrium
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The force that is trying to keep an atom or
molecule from leaving solution is both the
intermolecular bonds and the surrounding ambient
atmospheric pressure

• http//www.fact-index.com/b/bo/boiling_point.html

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It is kind of like a Rugby Scrum
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What if molecules in the interior of the liquid
acquire enough energy to leave the liquid phase
and go into the vapor phase?
At 100C the vapor pressure of water is 760 torr
(1 atm) or equal to the atmospheric pressure on
the liquid (in an open container) At this
temperature, interior bubbles will not collapse
and the water boils
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Mosh pit
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Atoms are constantly moving in and out of the
surface of a liquid.

• If the energy of a liquid reaches the Boiling
  point
• then molecules anywhere in the liquid begin to
  vaporize, resulting in the formation of vapor
  bubbles.

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If the ambient pressure is increased then a
greater vapor pressure is necessary for boiling
to occur.

• If the ambient pressure is decreased then a lower
  vapor pressure is necessary for boiling to occur.

If nearly all the ambient pressure is removed
then the vapor pressure will equal the ambient
pressure at room temperature
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The stronger the intermolecular bonds, the more
energy is necessary to break the bonds and create
vapor pressure. When the vapor pressure equals
ambient pressure the solution boils
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A substances state depends on temperature and
pressure

• Higher temperature than a liquid or gas
• Low temperature than a liquid or solid
• low pressure then a liquid or gas
• Higher pressure then a liquid or solid

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This relationship between pressure and
temperature can be studied best with a phase
diagram
The triple point is the only point where all
three phases are present at the same pressure and
temperature
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Each element or compound has a unique phase
diagram

• Uranium
• Hexafluoride

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Creating solid CO2 or H2O(l)
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Critical point
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Critical point

• At the critical point, the liquid phase becomes
  so energized and light that the liquid state is
  indistinguishable from the gas state and only a
  strange kind of vapor can be found.

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Moving from one phase to another is not as simple
or smooth as is portrayed on a phase diagram
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Superheating of a liquid

• Superheating can occur because bubble formation
  in the interior of the liquid requires many high
  energy molecule gathered together in the same
  vicinity

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We learned that q sh(mass)?T
The more heat the higher the temperature
something becomes
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Does water progressively heat up and just change
phase as it goes up?
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Does it stands to reason that the more heat
calories you put in an object the greater the
temperature and the matter just changes phase
no
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In reality when you take water and heat it up you
get a special graph
Heating curve
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These flats are area of phase change
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Why the plateaus, why the flat area what have we
missed in this despicable sorted story

• Why cant anything be simple???

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What do we know about these flat areas
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The energy necessary to cause vaporization of one
mole of a liquid its boiling point and at 1 atm
is heat of vaporization ?Hvap
This is the energy that is necessary to break
bonds
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What does that mean that the graph does not go up
but we are still pouring heat into the system?
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Remember the phase change is named in relation to
liquid water

• Heat of fusion water to ice
• or ice to water
• Heat of vaporization water to steam
• or steam to water

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When we reach 100 degrees the heat that is added
to the system is no longer increasing the
movement of the molecules but instead the
increased heat is used to
break hydrogen bonds
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Which takes more energy,Breaking the tight bond
of ice and convert the bond to a looser liquid
bond

• Breaking the liquid bond and allowing the H2O to
  become steam

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At 10 Co we add heat until the water is 0 Co
then we add additional heat to break the hydrogen
bond from the fused solid state into the liquid
state

• It takes 334J/g per gram to change ice into water.

Heat of fusion
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It is not enough just to get the water to the
proper 100 degree temperature we must also add
additional energy (2260J/g) to change the state
of the material itself.

• Heat of Vaporization

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This can be equated to the energy utilized to
break a spring
Here a spring is vibrating nicely
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Here the energy has tightened the spring
As you add heat energy the bond between molecules
is stretched
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Here the spring is energized to a taught state
where it can no longer increase vibration
What happens if you add more heat energy
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Here we see finally a broken spring and the ends
go flying apart.
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We need energy not only to stress the wire and
extend it to its full strength we finally need
the added extra energy to break the wire itself
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This is reversible process

• It takes energy going in to change 100 Co of
  liquid water into a gas
• And
• when 100 Co steam condenses to water energy is
  given off out of the water into the environment

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remember

• When ever there is a phase change energy is
  either consumed or expelled depending on the
  direction of the reaction
• solid to liquid fusion
• liquid to gas vaporization
•  

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How much energy does it take to change a liquid
to a solid or a liquid to a gas

• How much energy does it take to finally snap the
  bonds between the atoms or molecules

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It depends on how many bonds we need to snap It
depends on the mass

• q m heat of phase change

Heat of fusion for water is 334 J/g joules per
gram Heat of vaporization for water is 2269 J/g
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So to get water to become a gas 2260 J/g has to
be pulled in endothermically

• Why does getting sprayed with water so cooling on
  a hot day

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Some of the 2260 J/g heat of evaporation comes
from the air temperatureBut some of the 2260 J/g
comes from you skin leaving it feeling cold

• Heat leaves your skin and is used by the water to
  turn liquid water into vapor

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Calculate the heat required to change a 250 g
sample of liquid water at 100 Co into steam.
(Heat of vaporization of water is 2260 J/g)
q m heat of phase change

•   we are not talking about the energy to get
  the solution to boiling temp, we are talking
  about the energy to break the spring, vaporize
  the solution.

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Calculate the heat required to melt 15 g of ice
at 0 Co (heat of fusion for water is 334J/g)
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How much heat is released when 15 g of steam at
100Co condensed to give 15 grams water ( heat of
vaporization for water is 2260 J/g )
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How much heat is released when 15g of steam at
100oC condenses to give 15 grams of water at
100oC?
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So does this have anything to do with Lava-lamps?