Notes on Rates of Chemical Reactions

Rates of Chemical Reactions

• Definition: The rate of a chemical reaction is a measure of how quickly the reaction proceeds, determined experimentally.

• Fast vs. Slow Reactions:

  • Fast Reaction Example: Reactants A and B form product C.

  • At time = 0: Only reactants (A + B) are present.

  • After 30 seconds: All reactants converted to product C.

  • After 45 seconds: Still only product C present.

  • Slow Reaction Example: Reactants X and Y form product Z.

  • At time = 0: Only reactants (X + Y) are present.

  • After 15 seconds: Some reactants converted to product Z.

  • After 30 seconds: Reaction still ongoing.

  • After 45 seconds: Some reactants still present; not complete.

• Collision Theory:

  • States that chemical reactions occur through collisions between molecules.
  • Collisions must occur with sufficient energy for the reaction to proceed.

• Factors Affecting Reaction Rates:

  1. Concentration of Reactants:

     • Higher concentration increases the frequency of collisions.
     • Example: Reaction between hydrogen (H) and iodine (I) to produce hydrogen iodide (HI).
     • As concentration increases, likelihood of collisions increases leading to a faster reaction rate.
     • Note: Reaction rate decreases as reaction proceeds due to decreased reactant concentration.

  2. Temperature:

     • Higher temperature generally increases reaction rates.
     • Increased temperature leads to increased molecular motion, resulting in a higher frequency and energy of collisions.
     • Visual representation shows the same concentration at three different temperatures: low, intermediate, and high.
     • More molecular motion means more collisions at higher energy, increasing the likelihood of reactions.

• Summary of Factors Influencing Reaction Rates:

  • Rates increase with:
  • Increasing reactant concentration.
  • Increasing temperature.
  • Rates decrease as the reaction proceeds due to the reduction of reactant concentrations.