Bio

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Lecture 49
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Bio

• Albert Schweitzer

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Studied in Strasbourg and Parisat age 21 decided
to spend his first 30 years learning and the next
30 years serving humanity and God
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Schweitzer studied art music philosophy and
science

• In 1913 became a Medical doctor
• Was also a world class organist

After he was married Schweitzer spent his
remaining 50 years in Africa fighting leprosy and
sleeping sickness--a period of prodigious
philanthropy that earned him the Nobel Peace
Prize in 1952.
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Example is not the main thing in influencing
others, it is the only thing.
Albert Schweitzer
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the most urgent need expressed by The Paris
Missionary Society, turned him down!
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I am responsible Albert Schweitzer
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Albert Schweitzer

• The only ones among you who will be really happy
  are those who will have sought and found how to
  serve.
• --- Albert Schweitzer

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Homework review

• We know the concentration of the reactants
  increase the reaction rate
• But by how much?

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To determine how the concentration effects the
reaction rate we utilize the Rate Law

• Rate k reactantn

k rate constant at a given temperature reactant
the molarity of the reactant N the order of
the reaction
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The order of the reaction is important it tells
you the influence of the concentration

• Rate k reactantn

n can only be determined experimentally and are
usually whole numbers but are sometimes
fractions.
If n is 0 and there is only one reactant then it
is considered a zero order reaction and the
concentration has no effect on reaction rate If n
is 1 and there is only one reactant then it is
considered a first order reaction and the
concentration has a direct effect If n is 2 then
it is considered a second order reaction and the
concentration has a squared effect on reaction
rate
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2N2O5 ?4NO2 5O2Experimentally the rate was
found to be first order for N2O5 . That is the
rate varies directly with the N2O5 . Therefore
the following rate law can be written.Rate k
N2O51
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NO2 CO ?NO CO2Experimentally the rate was
found to be second order for NO2 and zero order
for CO . Therefore the following rate law can be
written.Rate k NO22 CO0
The effect of NO2 concentration squared and the
no effect from CO
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You can determine the order of a reaction by
comparing the rate of a reaction to the
concentrations
Rate k reactantn
There is a easier way (doubles)
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2ICl H2 ? I2 2HCl
When more than one reactant establish one
reactant as unchanging and calculate the others
order
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2ICl H2 ? I2 2HCl
Examine the Icl concentration between
experiment 1 and 2. What happens? (it doubles.)
What happens to the initial rate? (it doubles)
Therefore Icl is first order. What happens to
the H2 between experiments 1 and 3? (it
quadruples , four times greater) What happens to
the initial rate of the reaction? (it quadruples,
four times greater) Therefore H2 is first order.
(rate quadruples when concentration quadruples)
The rate law then is Rate k ICl1 H21
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The rate law then is Rate k reactant Ana
reactantBnb
Go over homework problems on page 595 1-10
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6) What is the order of a reaction if its rate
triples when the reactant concentration triples?

• 7) The reaction CH3NC ? CH3CN is of order 1, with
  a rate of 1.3 104 M/s when the reactant
  concentration was 0.040 M. Predict the rate when
  CH3NC 0.025 M.

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8)The following data relate to the reactionA B
? C. Find the order with respect to each
reactant.
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9) If the reactionNO2 CO ? NO CO2 proceeds
by a one-step mechanism,what is the rate law?
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http//www.saskschools.ca/curr_content/chem30/modu
les/module4/lesson3/ratelawequation.htm
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New HomeworkRead pages 604 to 611

• Do problems 1-9 on page 611

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Redox reactions

• The movement of electrons

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We have seen how the electron

• binds molecules
• accounts for electricity
• is the origin of electromagnetic waves
• accounts for all chemical reactions and therefore
  accounts for all life and matter.

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• Electrons put the zap in electricity, the color
  in light and the bang in many explosions.
  Electrons are what is makes elements stable when
  they are in their octet such as the Nobel gases
  or unstable when they are in anything but a
  octet.

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When you see metal rust, electricity flowing
from a battery or burning of gasoline you are
seeing the result of the movement of electrons
into around or out of a molecular system.
Magnesium oxygen gas ? magnesium oxide
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• Hundreds of years ago it was thought that all
  ionic reactions where there was a transference of
  electrons involved oxygen
• And they termed the transference of electrons and
  the ionic bonding oxidation

Addition of oxygen
4Fe 3O2 ? 2Fe2O3
Oxidation
CH4 O2 ? CO2 H2O
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The opposite of oxidation is oxygen removal of an
oxygen or what is called reduction
2 Fe2O3 3C? 3CO2 4Fe
Removal of oxygen
reduction
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More recently however we have learned that
oxidation and reduction reactions really involve
a much more fundamental and important process
then simply the addition or removal of oxygen.

• There is involved the invisible but powerful
  shift of electrons

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By following the shift of the electron we can
understand the chemical reaction from the view of
the electron where really all the energy lies

• It is kind of like studying a company by watching
  the employees move around but you get a better
  understanding by watching the money

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2Mg O2 ? 2MgOMg O2 ?MgO2
Which is correct?

• We know that Mg has 2 extra electrons
• We know the Oxygen needs 2 electrons
• 2Mg2 O2-2 ? 2MgO

This is ionic transfer of electrons
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But the old name oxidation reduction stuck
During a chemical reaction where there is a shift
in the placement of the electrons. This is called
an oxidation-reduction reaction. Oxygen does
not even need to be involved.
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Oxidation is the part of the process where there
is the loss of electrons

• During oxidation the electrons are pulled off
  leaving the compound with a more positive charge.
  The element that did the pulling of the
  electrons acquires the electrons and now has a
  more negative charge.

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Loss of two electron
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The oxidation reaction of Ca isCa ? Ca2 2e
The calcium has undergone oxidation and has lost
2 electrons
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Reduction is gain of electrons

• When a chemical undergoes reduction electrons are
  added leaving the primary material with a more
  negative charge. The element that gave up the
  electrons has a more positive charge. Again the
  products become ionic and stick together.

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Reduction is gain of electrons
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The reduction reaction of S is S 2e- ? S-2
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Reduction of sulfur
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These oxidation-reduction reactions always work
together. Electrons are removed from one element
or compound and then placed on another.

• Its like acid base chemistry where whenever a
  Hydrogen falls off an acid it is gained by a base

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Put together these reactions are seen Ca S ?
CaS
Ca loses two electrons (oxidation) and S gains
two electrons (reduction) and these now ionic
substances bond
This is nothing new!!!! We saw this happening
when we drew our Lewis dot reaction

• Ca ? Ca2 2e S 2e- ? S-2

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Notice the shift of the electrons with the
electrons oxidizing from the Ca and the sulfur
being reduced
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Any time a element or compound loses electrons
then it is undergoing oxidation no matter what
causes it. Any time an element or compound gains
electrons then it is undergoing reduction no
matter what causes the gain.
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Remember that LEO Loss of Electron
oxidation

• GER
• gain of electrons reduction

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Oxidation is when a Metal loses an electron so
that the original metal because more stable by
establishing an octet.

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• Reduction is when a Nonmetal gains an electron
  so that the valance shell of the element has a
  octet

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http//library.kcc.hawaii.edu/external/chemistry/i
ntroduction.html
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Li will do what , gain or lose an e- to be stable

• Li will undergo oxidation or reduction

Ca will do what to be stable
Ca will lose 2 e- to be stable so the Ca ends up
having undergone oxidation in order to establish
a stable shell
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To track the movement of the electron we use
oxidation numbers.If the oxidation number of an
atom or element changes that means there was a
transference of an electron and an electric
current was present
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The oxidation number is basically the charge on a
compound

• Kind of like in a poker game each different
  colored chip has a particular value

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To calculate the oxidation number

• 1)     the oxidation number for any free element
  or compound of identical free elements such as
  hoffbrinkel is 0
• 2)     the oxidation number for any ion is the
  charge on the ion
• 3)     the oxidation number for oxygen is 2
  except in peroxide (H2O2) when it is 1
• 4)     the oxidation number for H is always 1
  except when the H is attached to a metal in
  column 1 or 2 NaH BrH2 MgH2 where H -1
• 5)     all other oxidation numbers are assigned
  so that the sum of all oxidation numbers equals
  the net charge on the molecule or polyatomic ion

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Assign the oxidation numbers for

• CH4
• CO2
• N2O5
• Li4C
• SO3
• Na2O
• Cl-1
• PO4-3

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Assign the oxidation numbers for

• http//www.chemistrycoach.com/oxidation_numbers_ws
  _1.htmOxidation20Numbers20Worksheet-1
• http//www.howe.k12.ok.us/jimaskew/chemcard/redox
  3.htm

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• In order to understand these reactions we break
  the reactions into ½ reactions where the
  electron can more easily be tracked.
• Its kind of like using a microscope to see red
  blood cells in the blood. By taking the
  equation apart we can see where the electrons are
  moving.

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We separate the reactants into two equations ½
oxidation reaction and ½ reduction reaction.
Ca S ? CaS Ca ? Ca2 2e
S 2e ? S-2
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(No Transcript)
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Do some ½ reactions

• Zn(s) Cu2(aq) ? Cu(s) Zn 2(aq)
• Mg(s) Pb2 Mg2 Pb(s)
• Fe2O3 (aq) 3CO(g) 2Fe(l) 3CO2 (g)

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• Place the reactants on one side of the arrow
  and show where the electrons move accounting
  for the gain or loss of an electron and if this
  was a oxidation or reduction ½ reaction

The next step is making sure that all the
products and reactants including the electrons
are balanced.  
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Cuo Ag ? Cu2 Ag

• The half reactions are
• Cuo ? Cu2 2e oxidation
• Ag 1 e ? Ago reduction

Are the products balanced Are the reactants
balanced Are the electrons balanced
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• The overall reaction is
• Cuo ? Cu2 2e
• 2Ag 2 e ? 2Ago
• 2Ag Cu 2e ? 2Ag Cu 2e

2Ag Cu ? 2Ag Cu
This is another way to balance a chemical reaction
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What we are doing is balancing the equation from
the perspective of the electron. Which makes
sense because that really is where the chemical
reaction is taking place
This is nothing new!!!!!!!!!!!! We are just
understanding what we did before
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Cr3 Zno ? Cro Zn2

• Write the ½ reaction for Cr
• Write the ½ reaction for Zn

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• The half reactions are
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• Cr3 3e ? Cro reduction
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• Zno ? Zn2 2e oxidation

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To balance the electrons in the equations we must
multiply the Cr3 equation by 2 and the Zn
equation by 3 giving

• 2Cr3 6e ? 2Cro
  3Zno ? 3Zn2 6e
• 2Cr3 6e 3Zno ? 2Cro 3Zn2 6e

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Imagine the shift of the electrons from one
element to another. Notice how this means there
is a slight momentary electric current from the
element being oxidized to the element being
reduced
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The terminology that is used in these kind of
reactions is simple but important

• Oxidation is loss of electrons
• The oxidizing agent is the thing causing the loss
• The metal is undergoing oxidation
• Reduction is the gain of electrons
• The reducing agent is the thing causing the gain
• The nonmetal is undergoing reduction

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In the equation Ca S ? CaS the S is the
oxidizing agent or in other words the entity
forcing the loss of electrons to occur

• One way to remember the meaning of oxidizing
  agent, oxidation and oxidizing is to instead of
  using the word oxidation use the word clean

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Electrons are released in oxidation and acquired
in reduction
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In Ca S ? CaSThe element Ca loses 2 electrons
and is said to undergo oxidation and the Sulfur
gains 2 electrons so S is said to undergo
reduction.

• LEO GER
• Loss of Electron oxidation gain of electrons
  reduction

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Write a balanced equation for the reduction of
iron III ions to iron II ions by the oxidation of
neutral nickel atoms to nickel II ions
Fe3 e ? Fe 2 reduction Ni ? Ni2 2e
oxidation
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2Fe3 2e ? 2Fe 2 Ni ? Ni2 2e2Fe Ni
2e ? 2Fe Ni 2e
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Do the redox half reaction handout
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Elements are named in oxidation reduction
reactions by way of an Oxidation number, The
oxidation number specifies the number of
electrons that are being transported in the
reaction
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• In this classic reaction we can see how the
  electrons are transferred from the copper to the
  silver resulting in a flow of electrons.
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• Zn(s) Cu2(aq) ? Zn2(aq) Cu(s)

Zn0(s) ? Zn2(aq) 2e
2e Cu2(aq) ? Cu0(s)
here you can see the loss of electrons from the
solid zinc (oxidation) and gained by the solid
copper (reduction)
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When the ½ reactions represent a change of
oxidation numbers and therefore represents a
redox reaction

• Not all are reactions are redox reactions. Some
  reactions do not involve a transfer of electrons
  and resultant change in oxidization state.

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FeCl2 K2S ? FeS 2KCl

• A Classic reaction that is not a oxidation
  reduction reaction is the double replacement
  reaction. In the double replacement there is no
  exchange of electrons but instead simple a swap
  of one cation for another cation

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• FeCl2 K2S ? FeS 2KCl

This is not a redox reaction
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Redox reactions represent a deeper degree of
balance

• if there is a change in the oxidation number and
  there is a gain or loss of electrons then you
  have to keep track of the electrons there must
  be a equal number of electrons on both sides of
  the equation and ½ reactions. There can not be
  electrons lost into some cosmic abyss. There is
  a conservation of mass.

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OXIDATION NUMBERS

• Li has a oxidation number of 1
• Ca has a oxidation number of 2
• O2 has a oxidation number of -2
• F has a oxidation number of -1
• I has a oxidation number of -1
• Iron (III) has an oxidation number of 3

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These oxidation numbers are critical because they
let us know whether or not a electron is being
transferred and if the reaction is a redox
reaction.
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So as the elements combine and recombine the
electrons shift from one compound to another

• This transportation of electrons form one place
  to another is considered an electric current.
  For some elements this transference of the
  electrons is slow while for others compounds it
  is fast

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These electric currents are what causes batteries
to work
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Chemists can measure the electric potential that
is developed when these electric currents flow

• For instance
• F2 2e- ? 2F-
• Zn2 2e- ? Zn