Kinds of Chemistry

1
Chemistry is Imperfect

• Problem 1. Many possible reaction paths.
• We wrote CH4 2O2 ? CO2 2H2O
• But methane can also do this
• CH4 O2 ? CO 2H2O
• The second reaction makes deadly carbon monoxide
  the first produces only benign CO2 and H2O.

2
Imperfection happens.

• Problem 2. A second problem is that
• we may inefficiently isolate a product.
• product can stick to glassware.
• it can vaporize.
• it can get dropped on floor.
• it can stick to filter paper, etc.
• it can re-react (e.g., isolating K compared to
  Fe)
• Like gambling, there are many ways to lose!

3
Theory vs. Reality We actually quantify the
amount of imperfection.
Theoretical Yield what God would get. Percent
Yield what you would get compared to what God
would get as a chemist, expressed as a
percentage.
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Example 1 involves production of iron from iron
ore.
If you had 2 tons of rust (Fe2O3) how many tons
of iron could you get from it?
5
Lets do it by percent!
6
Or you can do it the hard way. (Having learned
conversions, might as well use them.)
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Suppose your metal processing plant loses some
iron and you only get 1.35 tons.

• Yield 100 x 1.35/1.40 96

8
Example 2 Soda lime glass is made from this
reaction Na2CO3 SiO2 ? Na2(SiO3) CO2
If we collect 200 g of CO2 from 1000 g of
sodium carbonate, what percent yield is that?

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10
Reactions do not go all the way.
Its not really A B ? C D Its more like A
B ? C D At any one time zillions of
As zillions of Bs zillions of Cs
zillions of Ds
Reactions that go More zillions of Cs and
Ds Reactions that dont go Less zillions of
Cs and Ds
11
Energy helps to determine whether reaction goes
or not (it is not the ultimate determinant,
though)
12
2 questions about reactions how fast? how far?
How fast
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Things that affect how fast include
Temperature rate ? as T ? Pressure rate ? as P
? Concentration rate ? as c ? Catalyst rate ?
Energy
AB
CD
With catalyst lowers energy of activation.
http//en.wikipedia.org/wiki/Enzyme
Time (reaction progress)
Biocatalyst Enzyme. Enzymes are important!
14
Things that affect how far
Chemists and, especially, chemical engineers who
try to manipulate equilibrium. Let me try to
explain..
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Equilibrium
Its more like A B ? C D zillions of As
zillions of Bs zillions of Cs zillions of
Ds
The molecules know what balance they want between
A, B, C and D. Problem is we may not
necessarily agree! Western cultures (and
chemists of all cultures) try to manipulate
equilibrium, as if it is our manifest destiny to
do so!
16
One of your first encounters with equilibrium was
physical equilibrium between gases liquids
solids. The Hot Soup Problem (Its alphabet
souphence the letters).
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Why is equilibrium such a foreign concept? 
Because we are used to fairly small numbers in
our daily lives. There are things that go like
equilibrium, though. Example attentiveness
of spectators at a football game.
 "Concession customers" ? "Active spectators"
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Can we manipulate this? Yes, by realizing that
the equation is not complete.

•  Concession customers Scoring Drive
• Û
• Active spectators Hunger

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We can characterize this equilibrium by a number,
the equilibrium constant, that shows the ratio
of product to reactant.
20
Limits to Equilibrium
What happens if we run out of Tiger Dogs? What
happens if the food lines are too long? What
happens if the oceans run out of capacity to
buffer all the CO2 we are producing?
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Returning to the soup problem
Hot soup ? Cold soup Heat released If we
remove heat from the soup in the form of hot
vapor, the system will try to make more heat in
the space above the soup. When it does, we get
more cold soup. Blowing on soup is manipulating
equilibrium!
Heat Energy H2O(l) ? H2O(g) Equilibrium
between water  liquid and water vapor.
22
Le Chateliers principle
23
Spontaneity!
Who decides what's equilibrium? Which way to
equilibrium? Observation often, the
reactions that occur spontaneously release heat
energy (exothermic). But not always! Some
endothermic reactions also occur spontaneously.

24
Entropy
Reactions (changes) occur if they increase the
disorderliness of the universe. Disorderliness"
is called "entropy" No one knows why this law
holds true. Like any law, it's the sum total of
our EXPERIMENTAL observations. You actually
take much of this for granted, whether you
realize it or not, when you use time Entropy is
time's arrow. "Forward" in times means more
disordered!