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Chapter 18 “Reaction Rates and Equilibrium”
Activation Energy
is being supplied
Activated Complex
1
Turn to page 62 in your Standards
Book
Standard #8 - Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules.
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Collision Theory Reactions can occur:
Very fast – such as a firecracker
Very slow – such as the time it took
for dead plants to make coal
Moderately – such as food spoilage
Rate of reaction means how fast is the
reaction
In chemistry, reaction rate is expressed as the
amount of reactant changing per unit time.
Example: 3 moles/year, or 5 grams/second
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Reaction rate
Rusting is a ‘slow’ reaction, you hardly see any change looking at it!
The fermentation of sugar to alcohol is quite slow but you can see the carbon dioxide bubbles forming in the 'froth'!
Burning of a fuel is an example of a fast reaction
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Rusting Pipe - Slow reaction
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Wood Burning - Fast Reaction
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I wonder what
happens if I mix
these two
solutions…
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8
WOW, that was
really FAST
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It was also
really FUN
10
I wonder if I should
be wearing my
goggles?
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Collision Model
•Key Idea: The molecules must
touch (or collide) to react.
•However, only a small fraction of
collisions produces a reaction. Why?
•Particles lacking the necessary
kinetic energy to react will bounce
apart unchanged when they collide 12
Collision Model 1. Collisions must have enough
energy to produce the reaction: must equal or exceed the “activation energy”, (which is the minimum energy needed to react).
Will a AA battery start a car?
• Think of clay clumps thrown together gently – they don’t stick, but if thrown together forcefully, they stick tightly to each other.
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Collision Theory
2. Also In order for reactions to
occur between substances,
their particles must collide and
the reactant molecules must be
correctly oriented for the
reaction
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Effective Collision
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Ineffective Collision
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