Factors affecting reaction rates

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Factors affecting reaction rates

• For students!

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The nature of reactants

• Some things just react more that is why sodium
  reacts with water but a metal like iron reacts
  slowly!
• Sodium is more reactive!

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Sodium in water

• The sodium is so reactive it has a very fast
  rate. It gets so hot that the hydrogen produced
  catches alight.

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The effect of concentration

• As concentration increases what happens to the
  rate according to collision theory?

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The effect of concentration

• As molecules become closer, more concentrated,
  they have a greater chance of colliding, this
  means that the chance of a successful collision
  through the correct orientation occurs, so the
  rate increases.

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The effect of surface area

• As surface area increases what happens to the
  rate according to collision theory?

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The effect of surface area

• As a lump of sugar dissolves slowly compared to
  grains, so powders react faster than lumps. This
  is because more surface allows for more
  collisions. This means that the chance of a
  successful collision through the correct
  orientation occurs, so the rate increases.

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The effect of temperature

• As temperature increases what happens to the rate
  according to collision theory?

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The effect of temperature

• As molecules gain more kinetic energy, they move
  faster so colliding more. They also collide with
  more energy. These 2 factors increase rate.

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The effect of temperature

• As temperature increases by approximately 10K
  (10OC) rate doubles.

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The effect of temperature

• The shaded area represents molecules with enough
  activation energy. As temp increases, the number
  with enough energy increases.

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The effect of a catalyst

• As a catalyst is added, what happens to the rate
  according to collision theory?

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The effect of a catalyst

• A catalyst lowers the activation energy, this
  increases the chance of a successful collision.
  Enzymes are biological catalysts.

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The effect of a catalyst

• A negative catalyst slows a reaction down. The
  name given is an inhibitor.
• Where might inhibitors be of benefit?

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Types of catalysts.

• Catalysts can be homogeneous or heterogeneous. If
  the catalyst is in a different state to the
  reactants it is? The same state it is?

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Question

• Platinum is a solid metal used in catalytic
  converters in cars. As the exhaust fumes pass
  over they are turned into less polluting
  chemicals, what type of catalyst is platinum?
• Enzymes are in solution with the food. What type
  of catalysts are they?

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Answer Q11 - 14

• P541