Her parents encouraged her in chemistry and biology

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Lecture 42
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Her parents encouraged her in chemistry and
biology
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Dr. Hodgkin began her work at Somerville College
in Oxford in 1928

• Here, she discovered that crystals are a solid
  compound of atoms arranged in a regular and
  repeated pattern.

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Does the College matter??

• Dorothy Crowfoot married Thomas Hodgkin in 1937.
  Thomas was a distinguished historian of Africa
  and an Arab scholar. He was the son of Robin H.
  Hodgkin, provost of Queen's College in Oxford and
  cousin of Professor A. L. Hodgkin, a recipient of
  the Nobel
  Prize for medicine in 1963.

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Dr. Hodgkin hooked up with WL Bragg Nobel
laureate for crystallography
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In 1944 she found the structure of penicillin
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• Dr. Hodgkin began working on Vitamin B12 which
  prevents and cures pernicious anemia in the late
  1940s. She finally determined the structure of
  Vitamin B12 in 1956. For this, as well as here
  other achievements, she won the Nobel Prize in
  chemistry in 1964.

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Dorothy Crowfoot Hodgkin suffered a stroke and
died July 29, 1994 at her home in England
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Homework read pages 496 511

• Page 501 do problems 1-7
• Page 511 do problem 1-7

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Go over exam written part

• Block 2 will take the test for the first 45 min
  next class

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Last time we talked about

• How like dissolves like
• Polar grabs polar hydrophilic
• Nonpolar mixes with nonpolar hydrophobic
• Soap with the polar head and nonpolar tail allow
  nonpolar to be hydrated

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We saw the difference between solvent and solute
There is more solvent
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To quantitate the degree of salvation
(concentration) we discussed molarity which
ismoles per liter

• M moles per liter

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In liquids the higher the temp the more solute
that can be added until you hit the saturation
point

• Unsaturated
• Supersaturated
• saturated

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When mixing gases in liquid the hotter the system
the less gas that goes into solution
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And lastly we discussed Colligative properties

• Adding a solute into a solution gets in the way
  of the freezing process so it takes a lower temp
  for freezing
• Adding a solute into a solution getts in the way
  of vaporization so it demands a greater
  temperature for boiling

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Pure water vaporization At 100 C
Impure water vaporization At 104 C
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Today Reaction equilibrium
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In a simple world opposites attract and they stay
together
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But associations do not always stay together
There are Clues that indicate If the association
is reversible
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The same goes with chemicals
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Equilibriumis when the forward reaction equals
the reverse reaction
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To understand the way a chemical reaction shifts
from reactions to products we look at the
equilibrium.
In chemistry we used the arrows to illustrate the
tendency for a reaction to go to the product side
or reactant side
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These are called completion reactions One way
reactions

• According to the arrows these reactions only move
  in one direction
• (Like playing tennis by yourself)

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In the reaction PCl3 Cl2 ? PCl5 we know that
in a perfect world 1 mole of PCl3 one mole of Cl2
should react and be used up yielding 1 mole PCl5.

But that is not what happens because of the ?
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• These are called reversible reactions

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Look at the reaction 2NO2 ? 2NO O2

• Initially you have a ton of NO2 that is turning
  into NO and O2 quickly because of the great
  quantity of NO2 present
• With time you start to have less NO2 and so the
  reaction slows down because of the low quantity
  of NO2 present

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This is a tug of war where you have flow toward
the left (reactants)flow toward the right
(products)
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Graph of the change in the number of moles of NO2
with time
As you use up the NO2 your reaction rate slows
down
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According to the graph does all the NO2 get used
up
Why Not? ?
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2NO2 ? 2NO O2As NO2 dissociates you go from a
state where there is no O2 to where there is some
O2 and in time a great deal of O2
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The same goes for NO
Depending on the rate of dissociation of NO2
and the rate of recombination of O2 and NO you
get a balance.
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Why aren't the NO and the O2 lines the same?
2NO2 ? 2NO O2
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The number of O2 and NO that are combining and
becoming NO2 then the chemical reaction is said
to be in
When the number of NO2 atoms decomposing and
become O2 and NO equaled
equilibrium
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The concept that concentration pushes a reaction
is called the Law Of Mass Action It basically
states that the rate of a chemical reaction is
proportional to the concentration of the
reactants.
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We can convey the direction and rate of a
reaction by using the ratio of products to
reactants A ratio of 1 means as much goes forward
toward product as back toward reactant A ratio of
½ means for every one that goes forward two go
back more reactant than product
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They found that if you take the molar
concentration of the products and divide by the
molar concentration of the reactants you get a
constant Keq for that particular chemical
reaction.
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PCl3 Cl2 ? PCl5
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PCl3 Cl2 ? PCl5

• For our reaction PCl3 Cl2 ?PCl5 where the
  reaction reaches an equilibrium where 1M PCl3
  reacts with 1 M of Cl2 stabilizing at a
  concentration of
• .76 M of PCl3 .76 M Cl2
• and
• .26 M of PCl5.

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calculating the Kequ we get 0.47
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• Equilibrium of the flow out to flow in

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H2 Cl2 HCl under heated conditions

• 1.9 moles per liter of the product and .01 moles
  per liter of the reactants

Note there is no units on Kequ it is a ratio
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 A 2B ? 3C

• A BB ? CCC

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So write the equilibrium constant equation
forthe Haber process for making NH3

• N2(g) 3H2(g) ? 2NH3(g)
• COCl2(g) ? CO(g) Cl2(g)
• Fe(aq) SCN-(aq) ? FeSCN2(aq)

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• H2 Cl2 ? 2HCl
•   2NO2(g) ? N2O4(g)
•     2HI(g) ? H2(g) I2(g)
•  
• 2SO2(g) O2(g) ? 2SO3(g)

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The greater the concentration the greater the
rate of the reaction. What would the
concentration of a pure solid (s) or pure
liquid (l) be
By definition a pure solid or pure liquid has no
solvent so the concentration is nonsensical.
Therefore you simply leave all solids and pure
liquids out of the equation.
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Write the equation for Keq for the below
equations

• 8) 2NO(g) O2(g) ? 2NO2(g)
•   
• 9)     CO(g) H2O(g) ? CO2(g) H2(g)
•  
• 10)H2(g) Cl2(g) ? 2HCl(g)
•  
• 11)Cu(s) 2 Ag (aq)? Cu2 (aq) 2Ag(s)
•  
• 12)PbI2(s) ? Pb2 (aq) 2I-(aq)
•  

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Think of the difference between the numerator and
denominator
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• 9)     Ag (aq) 2NH3(aq) ? Ag(NH3)2(aq)
•  
• 10)4HCl(g) O2(g) ? 2H2O(g) 2Cl2(g)  
• 21) C (s) 2H2(g) ? CH4(g)
•  
• 22) C(s) H2O(g) ? CO(g) H2(g)
•  

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• For the reaction where
• H2CO3 (aq) H2O (l) ? H3O(aq) HCO3-(aq)
•  
• what is the Keq value realizing that at
  equilibrium and in a closed system
•  
• 1) H2CO3 (aq) 3.3x10-2 M
• 2) H3O(aq) 1.1 x 105 M
• 3) HCO3-(aq) 7.1 x 10-1 M
• 4) H2O (l) nonsensical

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• For the system involving N2O4 and NO2 at
  equilibrium
• (N2O4(g)? 2NO2(g))
• at a temperature of 100oC the concentration of
  N2O4 is
• 4.0 x10-2M and the concentration of NO2 is 1.2
  x 10-1 M. What is the Keq for this reaction

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• Methanol can be prepared by the reaction of H2
  and CO at high temperature , according to the
  following equation,
• CO(g) 2H2(g) ? CH3OH(g)
•  
• What is the concentration of CH3OH(g) if H2
  0.08 M and CO .025M and the Keq for the
  reaction is 290

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a) enable you to estimate the concentration of
reactants at equilibrium at a particular
temperatureb) indicate the direction of the
reactionc) enable you to estimate the
concentration of reactants at equilibrium at a
particular temperature
Remember that the Kequ gives you a quantitative
idea of the