17.2 What Determines ROR?

• Effective Collisions:

  • when a chemical reaction occurs btw particles
  • particles must collide with energy >/= to activation energy (min. amount of energy taken in for bond breaking)
  • more effective collisions - increased ROR
• 1. Concentration

  • number of particles in given volume
  • as concentration of reactants increase, number of reacting particles per unit volume increases
  • particles collide more frequently - frequency of effective collisions increase
• 2. Pressure (only for gases)

  • gases compressed to smaller volume - more gaseous particles per unit volume - pressure increase
  • particles closer tgt - collide more frequently - increased frequency of effective collisions - increased ROR
• 3. Particle Size (Surface Area)

  • breaking a large particle into smaller pieces - more finely divided - surface area increase (total mass and volume remains constant)
  • SA in contact with other reactant particles increase - higher frequency of effective collisions - increased ROR
• 4. Temperature

  • 2 ways particles are affected: reactant particles have more KE - move and vibrate faster - increase frequency of effective collisions + more reactant particles possess energy >/= to Ea - increase frequency of effective collisions