Rates of Reaction

Chemistry AS :)

Definitions and how to explain:

  • The Collision Theory
  • Increasing Concentration/ Pressure on the rate of reaction
  • Increasing Temperature on the rate of reaction
  • Addition of a Catalyst on the rate of reaction
  • Activation Enthalpy
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  • Created by: VicC
  • Created on: 25-05-09 20:49

Rates of Reaction

affected by:

  • concentration
  • pressure
  • a catalyst
  • intensity of radiation
  • surface area
  • particle size
  • temperature
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THE COLLISION THEORY

For a reaction to occur, reactant particles must collide AND their combined kinetic energy must be equal to or greater than the activation energy for the reaction.

(http://woodlawnautobody.files.wordpress.com/2009/04/kf_collision2.jpg)

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Affecting the Rate of Reaction...

increasing CONCENTRATION/ PRESSURE:

  • means more particles per cm3
  • hence, more collisions per second
  • hence, rate of reaction INCREASES

! no mention of activation energy !

(http://wwwsci.seastarchemicals.com/images/faq_co3.jpg)

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Affecting the Rate of Reaction...

increasing TEMPERATURE:(http://www.learner.org/courses/essential/physicalsci/images/s7.thermometer.jpg)

  • particles have more kinetic energy
  • so collisions have more knietic energy
  • collisions occur more frequently
  • as a greater proportion of collisions will equal or exceed the minimum activation energy needede to react
  • hence, the rate of reaction INCREASES
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Affecting the Rate of Reaction...

addition of a CATALYST:

  • provides an alternative pathway for the making and breaking of bonds
  • hence, providing a lower activation energy
  • so a greater proportion of collisions will equal or be greater than the minimum activation energy needed for the reaction to occur
  • hence, the rate of reaction INCREASES
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ACTIVATION ENTHALPY/ ENERGY

  • The minimum combined kinetic energy required by a pair of colliding particles before a reaction will occur.

or

  • The energy required to allow bonds in the reactants to stretch and break as the new bonds form in the products.
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