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Chemistry 121

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Chemistry 121. Week of 3. January / February ... Kinetic Molecular Theory ... To match the collision frequency of the molecule, you would drive 2.8 x 109 mi ... – PowerPoint PPT presentation

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Title: Chemistry 121


1
Chemistry 121
  • Week of 3
  • January / February 2007

2
Exam 1 Results
  • Grading Scale
  • 4.0 100-92
  • 3.7 91-88
  • 3.3 87-82
  • 3.0 81-78
  • 2.7 77-74
  • 2.3 73-68
  • 2.0 67-64
  • 1.7 63-60
  • 1.3 59-55
  • 1.0 54-50
  • 0.0 49-0

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Boiling Point of Water as a Function of Pressure
  • Water boils at lower temperatures as altitude
    (height above sea level) increases. This table
    shows the temperature of boiling water at various
    altitudes
  • The boiling points of all liquids will be
    similarly affected. What sorts of things might be
    affected by the lower boiling points of water and
    other liquids?

5
Boyles Law
6
Avogadros Law
7
Relationship between Temperature/Pressure
8
Charles Law
9
Check-In
  • Oxygen generators in some airplanes are based on
    a chemical reaction between sodium chlorate and
    iron
  • NaClO3 (s) Fe (s) ? O2 (g) NaCl (s) FeO(s)
  • How many grams of NaClO3 would be needed to
    produce 120. liters of O2 at 1.00 atm and 20. C?

10
Collecting gas sample over water
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Kinetic Molecular Theory
  • Gas molecules can be considered to have
    negligible volume (compared to container).
  • Gas molecules are in constant motion and
    frequently collide (elastic) with each other and
    the walls of the container.
  • Gas molecules do not exert attractive or
    repulsive forces on each other.
  • The average kinetic energy of the molecules is
    proportional to the absolute temperature of the
    gas.

13
Where Does Pressure Come From?
  • To give you an idea of relative speeds and forces
    of collisions
  • Consider a N2 molecule the size of a compact car.
    To match the collision frequency of the
    molecule, you would drive 2.8 x 109 mi/sec and
    smash into another car every 700 yards without
    sustaining any damage.

14
Motion of a Gas Molecule
15
Pressure and Volume
  • Distance between molecules?
  • What happens to the number of collisions?
  • Speed of gas molecules?

16
Partial Pressure
  • Distance between molecules?
  • Number of collisions?
  • Speed of molecules?

17
Temperature
  • Speed of molecules?
  • Distance Between Molecules?
  • Number of Collisions?

18
Number of Atoms?
  • Distance Between Molecules?
  • Number of Collisions?
  • Speed of molecules?

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Check-In
  • During the decomposition of KClO3, 92 mL of O2 is
    collected by displacement of water at 25 C.  If
    atmospheric pressure is 756 mm Hg, what mass of
    O2 is collected? 

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Check-In Continued
Why Do We Store Energy as Fat... Animals, though
they store small amounts of glycogen in the
muscles and liver, and rely on glucose in the
bloodstream for immediate energy needs, bank most
of their energy reserves in fat.  The body of a
typical woman is about 25 fat by weight (a man's
body is closer to 15).  In a world where
swiftness and agility increase an animal's
chances for survival, is it better to store
energy as fat or carbohydrates?
25
a.) How many grams of weight is attributed to
fat storage in a 150. lb woman?  (Remember 1lb
453.6g.)
150. lbs x .25 37.5 lbs fat 37.5 lbs x
(453.6g/1lbs) 17,010 g fat
b.)  Fat releases 9.0 cal/g of energy when
burned.  How many calories (cal)  are released
when the woman in part (a) burns all of her fat
reserves?
17010 g fat x 9.0 cal/g 153,090 cal
26
c.)  Carbohydrates release 4.0 cal/g when
burned.  How many grams of carbohydrates contain
this same amount of energy, as found in part (b)?
153090 cal ? 4.0 cal/g 38,272.5 g carbohydrates
d.)  Using your answer to part (c) and
information from part (a), what would be the
total weight of this woman, if her body stored
this energy in carbohydrate reserves?
38,272.5 g ? 453.6 g/lb 84.38 lbs 150. lbs
37.5 lbs fat 112.5 lbs 112.5 lbs 84.4 lbs
carbs 196.9lbs or 2.0 x 102 lbs
27
Why Store Energy in Fat Reserves????
  • Therefore, a 150 lbs woman would weigh 200 lbs,
    if energy was stored by our bodies in the form of
    carbohydrates instead of fats!!!!!

But, why the difference between the energy of
fats and carbohydrates?
Fat triglyceride
Carbohydrate sucrose
See p. 351, Silberberg for more pictures
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