Rates and Equilibrium Notes, part I

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Rates and Equilibrium Notes, part I

• Collision Theory
• Factors Affecting Reaction Rates

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Reaction Rates

• We have talked about many reactions so far, but
  we have not talked about how fast a reaction
  occurs.
• A reactions rate is the speed at which it will
  occur.

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Collision Theory

• Reactions occur when atoms, ions or molecules
  collide, providing that they have enough energy
  to do so.
• Why only if they have enough energy?

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Activation Energy

• Activation energy is the minimum amount of energy
  particles need to react with each other.

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Orientation

• Atoms also have to collide in the right
  configuration to react.

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Reaction Mechanisms

• Because molecules have to collide to react, large
  reactions with lots of reactants do not happen at
  once.
• A reaction mechanism is the series of steps that
  take place.
• See board for example and graph.

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Factors Affecting Reaction Rates

• Every reaction proceeds at its own rate, but by
  modifying the conditions a reaction takes place
  in, we can change the speed reactions occur.

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1) Temperature

• Usually, raising the temperature of a reaction
  speeds up a reaction (the opposite is true, as
  welllowering temperature slows down reaction).
• Why?

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1) Temperature

• As the temperature of particles increases, their
  overall energy increases (increasing the chance
  that there will be enough energy for the
  reaction). Also, the faster moving particles are
  more likely to collide.

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2) Concentration

• Generally, increasing concentration of reactants
  increases a reactions rate.
• Why?

No, not THAT kind of concentration!
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2) Concentration

• Because you have more particles in the same
  amount of space (the same volume) there are more
  collisions, thus more chances each second for the
  reaction to occur!

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3) Particle size

• Decreasing the particle size for the same amount
  of reactant will cause the reaction rate to
  increase.
• Why?

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3) Particle size

• Decreasing particle size increases the total
  amount of reactant exposed for reaction. The
  more exposure, the more likely that collisions
  will occur and thus, a faster reaction!

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3) Particle size

• Surface area is the same idea, but looked at in
  the opposite way.
• The smaller particle size for the same amount of
  stuff, the higher the surface areaso the higher
  the surface area, the faster the reaction.

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4) Catalysts

• A catalyst is something that speeds up a reaction
  without being used up.
• How does it work?

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4) Catalysts

• Catalysts allow a reaction to proceed at a lower
  than normal activation energy.
• It can do this by forming an alternate route
  for the reaction to occur, sometimes allowing for
  an intermediary product.

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4) Catalysts

• Other catalyst terms
• An inhibitor is a substance that acts against the
  effects of a catalyst.
• An enzyme is specifically a biological catalyst
  usually composed of a protein.