1. Chemistry
Chapter 2 - Section 2
Rates of
Chemical
Reactions

Tuesday, July 10, 2012

2. How Fast?
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3. Some reactions need
some help to get started,
others do not.
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4. “What is
that extra help
called?”
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5. Activation
Energy
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6. The
minimum amount
of energy needed to
start a reaction.
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7. Let’s look at an
example:
2O2 + CH4 --> CO2 + 2H2O
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8. Tuesday, July 10, 2012

9. Activation Energy
9
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10. Activation Energy
For a reaction to begin, the molecules must
bump into each other or collide with enough
force.
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11. Activation Energy
For a reaction to begin, the molecules must
bump into each other or collide with enough
force.
The reactants must smash into each other
with a certain amount of energy. If they do
not, the reaction will not occur.
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12. Activation Energy
For a reaction to begin, the molecules must
bump into each other or collide with enough
force.
The reactants must smash into each other
with a certain amount of energy. If they do
not, the reaction will not occur.
This energy is called, activation energy.
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13. Activation Energy
For a reaction to begin, the molecules must
bump into each other or collide with enough
force.
The reactants must smash into each other
with a certain amount of energy. If they do
not, the reaction will not occur.
This energy is called, activation energy.
This is also true for reactions that release
energy when they react. An example is
gasoline burning. 9
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14. When gasoline is spilled it does
not burst into flames.
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15. A highly flammable material, which
cannot be extinguished by wind or rain
needs to be lit in order to burn.
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16. Rate of Reaction?
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17. How fast a reaction
occurs after it has
started.
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18. You can measure
Reaction Rate by:
- how quickly one of the
reactants is consumed,
or
- how quickly one of the
products is created
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19. Rate of Reaction -
The faster the better
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20. Rate of Reaction -
Fast is not good here
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21. What controls
reaction rate?
1. temperature
2. concentration
3. surface area
4. inhibitors
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22. Temperature
Changes Rate
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23. Temperature
Changes Rate
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24. Temperature
Changes Rate
Slow the ripening of fruit by putting them in the
refrigerator.
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25. Temperature
Changes Rate
Slow the ripening of fruit by putting them in the
refrigerator.
Meat and fish decompose faster at higher
temperatures, producing toxins that can make
you sick. Keep them chilled helps slow the
decomposition rate.
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26. Temperature
Changes Rate
Slow the ripening of fruit by putting them in the
refrigerator.
Meat and fish decompose faster at higher
temperatures, producing toxins that can make
you sick. Keep them chilled helps slow the
decomposition rate.
Bacteria grow faster at higher temperature.
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27. Temperature Affects Rate
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28. Temperature Affects Rate
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29. Temperature Affects Rate
Most chemical reaction speed up when
temperature increase.
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30. Temperature Affects Rate
Most chemical reaction speed up when
temperature increase.
The atoms and molecules are always
moving, and they move faster at higher
temperatures.
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31. Temperature Affects Rate
Most chemical reaction speed up when
temperature increase.
The atoms and molecules are always
moving, and they move faster at higher
temperatures.
Faster molecules collide with each other
more often and with greater force,
which may be enough to break the old
bond. This is activation energy.
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32. Concentration
Affects Rate
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33. Concentration?
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34. Amount of substance
in a certain volume.
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35. Surface Area Affects Rate
10 cm
10 cm
10 cm
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36. Surface Area Affects Rate
Surface Area = 600 cm 2
10 cm
10 cm
10 cm
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37. Surface Area Affects Rate
Surface Area = 600 cm 2
10 cm That is the
amount of
10 cm
surface that
10 cm would be
touching the
other
reactant.
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38. Surface Area Affects Rate
What if we cut out little cubes?
1cm x 1cm
10 cm
10 cm
1 cm
1 cm
10 cm
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39. Surface Area Affects Rate
What if we cut out little cubes?
1cm x 1cm
10 cm How many cubes
10 cm
would we have?
1 cm
1 cm
10 cm
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40. Surface Area Affects Rate
What if we cut out little cubes?
1cm x 1cm
10 cm How many cubes
10 cm
would we have?
1 cm
1 cm 1000 cubes
10 cm
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41. Surface Area Affects Rate
What if we cut out little cubes?
1cm x 1cm
10 cm How many cubes
10 cm
would we have?
1 cm
1 cm 1000 cubes
10 cm
What would be
the SA of one
of the cubes?
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42. Surface Area Affects Rate
What if we cut out little cubes?
1cm x 1cm
10 cm How many cubes
10 cm
would we have?
1 cm
1 cm 1000 cubes
10 cm
6cm2 What would be
the SA of one
of the cubes?
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43. Surface Area Affects Rate
What is the total SA of all the cubes?
10 cm
10 cm
10 cm
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44. Surface Area Affects Rate
What is the total SA of all the cubes?
10 cm 6cm 2 x 1000 =
10 cm
10 cm
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45. Surface Area Affects Rate
What is the total SA of all the cubes?
10 cm 6cm 2 x 1000 =
10 cm
6000 cm 2
10 cm
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46. Surface Area Affects Rate
What is the total SA of all the cubes?
10 cm 6cm 2 x 1000 =
10 cm
6000 cm 2
10 cm
SA of Whole cube = 600 cm 2
SA of cut up cube = 6000 cm 2
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47. Surface Area Affects Rate
10 cm
That’s a
BIG
difference!
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48. Surface Area Affects Rate
SA of Whole cube = 600 cm 2
SA of cut up cube = 6000 cm 2
10 cm
That’s a
BIG
difference!
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49. Slowing
Down
Reactions
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50. Inhibitor?
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51. A substance that slows down a
chemical reaction. An inhibitor
makes the formation of a
certain amount of product take
longer.
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52. Inhibitor
Butylated hydroxytoluene (BHT)
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53. Speed Up Reactions
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54. Catalyst?
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55. A substance that speeds up
a chemical reaction.
Catalyst’s do not appear in
a chemical equation
because they are not
changed permanently or
used up.
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56. Catalysts
- provide a surface for
the reaction to take
place,
or
- reduce the activation
energy needed to start
the reaction
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57. 37
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58. Catalytic Converter
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59. Catalytic Converter
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60. Catalytic Converter
In vehicles, the exhaust passes through the
catalyst.
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61. Catalytic Converter
In vehicles, the exhaust passes through the
catalyst.
Catalysts will speed up the reactions that
change incompletely burned substances that
are harmful, such as carbon monoxide, into
less harmful substances like CO2 and H2O.
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62. Catalytic Converter
In vehicles, the exhaust passes through the
catalyst.
Catalysts will speed up the reactions that
change incompletely burned substances that
are harmful, such as carbon monoxide, into
less harmful substances like CO2 and H2O.
This results in cleaner air.
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63. Catalytic Converter
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64. Catalytic Converter
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65. Enzymes are Specialists!
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66. Enzyme?
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67. Large protein molecules that
speed up reactions needed for
your cells to work properly.
- convert food to fuel
- build bone and muscle tissue
- convert extra energy to fat
- produce other enzymes
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68. Tuesday, July 10, 2012

69. Other Uses of Enzymes
One example is Proteases - a class of enzymes
that work within cells to break down proteins.
Meat tenderizer is one example of a protease.
Contact lens cleaning solutions also contain
proteases that break down proteins formed by
your eyes that can collect on your lenses and
cloud your view.
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70. Finished
the KNP!
So, lets see a
catalyst at
work!
Tuesday, July 10, 2012