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Unit 8: Rates of Reactions
Collision Theory
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Collision Theory In order for a reaction to occur… Reactants must collide 1 2 Collision must be at the correct orientation 3 Collision must have minimum amount of energy for bonds to break Only a small number of collisions meet the requirements and result in a reaction
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1. Reactants Must Collide
In order for two molecules to react, they must come in contact with one another N O F There’s no way they’ll ever react if they don’t run into one another!
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2. Collision with Incorrect Orientation
For a collision to result in a chemical reaction, it must occur with the correct orientation N O F This is not the correct orientation. The reaction will not happen.
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2. Collision with Correct Orientation
For a collision to result in a chemical reaction, it must occur with the correct orientation F N O N O But not every collision produces a reaction—they must collide in the correct orientation to react F F This is the correct orientation. The reaction will happen.
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3. Collision with Not Enough Energy
For a collision to result in a chemical reaction, it must occur with the minimum energy for reaction Temperature: 10 oC N O F The collision does not have enough energy to produce a reaction
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3. Collision with Enough Energy
For a collision to result in a chemical reaction, it must occur with the minimum energy for reaction Temperature: 28 oC F N O N O F F This collision had more energy (faster moving molecules). A reaction will occur..
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Factors Affecting Reaction Rate
Temperature Concentration Surface Area Catalysts
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For most reactions, as temperature increases, reaction rate increases
Higher Temperature = faster molecules Faster molecules: More likely to collide Higher energy when they collide Reaction more likely to happen For most reactions, as temperature increases, reaction rate increases
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Concentrations of Reactants
More reactants = more likely to collide Reaction more likely to happen For most reactions, as reactant concentration increases, reaction rate increases
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Surface Area of Reactants
Higher surface area = reactants more likely to collide Reaction more likely to happen As surface area increases, reaction rate increases
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Catalysts Catalyst: – a substance that increases the rate of reaction without being used up creates a lower energy reaction pathway Example: enzymes in the body
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