Topic: Kinetics
description
Transcript of Topic: Kinetics
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Topic: Kinetics
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2 things needed for a reaction to occur
• X amount of activation energy• Effective collisions
Particle Diagram of Collision
NO + O3 NO2 + O2
Activated Complex is NOT in equation!
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Kinetics tells how fast a reaction will occur
• Reaction rate = speed of the reaction– Depends on Frequency of collisions (how often
they occur) and efficiency of collisions• Rate = Concentration of reactant or product
timeDisappearance of reactants
Appearance of products
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Collision Theory• Molecules must collide in order to react• Effective collisions lead to formation of products– Effective Collisions =
• Energetic• Favorable orientation
• Ineffective collisions do not lead to products
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Most collisions are NOT effective!
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Why Do Collisions Have to be Energetic?
• KE of reactants is used to overcome reaction barrier
• KE is transformed into PE
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)
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Nature of the reactants:Ions or Molecules?
• Ions in solution react quickly• Covalently bonded molecules react slowly– takes time to break all those bonds!
• 2 gas phase reactants react more quickly than 2 liquids or 2 solids
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)2) Temperature
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Increase in Temperature
• Temp = measure of average KE of molecules in system
• faster molecules are moving, will collide more often
• faster molecules are moving, more energetic the collisions
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)2) Temperature3) Concentration
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Concentration
• Increase in concentration:– more particles per unit volume – more collisions in given amount time
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)2) Temperature3) Concentration4) Pressure (gases only)
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Pressure
• systems involving gases changing pressure analogous to changing concentration
• Pressure, # particles per unit volume– Increase reaction rate
• ↓ Pressure, ↓ # particles per unit volume– Decrease reaction rate
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)2) Temperature3) Concentration4) Pressure (gases only)5) Surface Area
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Surface Area
• Higher surface area –more particles exposed for reaction
• Higher surface area means smaller particle size• (For heterogeneous reactions)
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• Homogeneous Reaction: –all reactants in same phase
• Heterogeneous Reaction: –reactants in different phases
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Factors that determine reaction rates
1) Nature of reactants (ions vs molecules)2) Temperature3) Concentration4) Pressure (gases only)5) Surface Area6) Presence of a catalyst
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Catalyst
• Substance that increases rate of reaction without itself being consumed –does not participate in reaction
• Lowers the activation energy for the reaction
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Catalyst/enzyme written above the arrow