Collision Theory

• Reactions must be controlled

  To avoid excess heat production
• Uncontrolled reactions


  Can cause unwanted side reactions or even explosions
• Collision Theory


  1. Reacting particles must collide

  2. Collision must have sufficient energy

  3. Collision geometry must be correct
• Activation energy (EA)


  The minimum energy required for a reaction to occur
• Activated Complex


  An unstable intermediate arrangement of atoms formed while bonds are breaking and forming
• Factors that affect the rate of reactions

  • Concentration
  • Size of particle (surface area)
  • Temperature
  • Pressure (for gas)
  • Use of catalyst
• Calculating relative rate


  Relative rate = (time (5) - time (1)) / time (5)
• The relative rate of a reaction which reached completion in 1 minute 40 seconds is 100/160 = 0.625
• More concentrated


  Faster reaction
• Effect of Particle Size

  • Smaller particles react faster
  • Smaller particles have larger surface area
• Higher pressure


  Faster reaction
• Higher temperature


  Faster reaction
• Energy distribution diagram


  The area under the graph indicates the total number of particles
• At higher temperature


  The graph shifts right, more particles have enough energy to react
• Catalysts


  Lower the activation energy
• Increasing temperature increases the number of molecules with sufficient kinetic energy to undergo an effective collision.
• Collisions that have enough kinetic energy to overcome the activation energy are called effective collisions, while those with insufficient energy are called ineffective collisions.
• A catalyst is a substance that speeds up a chemical reaction without being used up itself.
• An increase in concentration leads to more collisions per unit time, increasing the rate of reaction.
• A catalyst is a substance that lowers the activation energy required for a chemical reaction without being consumed or changed by the reaction itself.
• Surface area can affect the rate of reaction by providing more sites for collisions between reactant molecules.
• Particle size can also impact the rate of reaction, with smaller particle sizes leading to faster rates due to increased surface area.