Rates of reaction

• Average ROR


  Change in concentration / Total Time
• Endothermic reaction


  AH+ (positive)
• Exothermic reaction


  AH- (negative)
• Catalysts


  Substances that alter the rate of a chemical reaction but are not consumed in the reaction
• Rates of Reactions


  • Change in concentration per unit time of any one of the reactants or products in a reaction
• Factors affecting reaction rates


  • Nature of reactants
  • Particle size
  • Concentration
  • Temperature
• Ionic reactions


  Fast, do not involve breaking bonds
• Covalent reactions


  Slow, involve breaking bonds
• Instantaneous ROR


  Rate of reaction at any one point during the reaction
• Activation energy


  Minimum amount of energy which colliding particles must have for a reaction to occur
• Enzyme


  Biological catalyst
• Catalyst mechanisms


  1. Intermediate formation theory

  2. Surface adsorption theory
• Types of catalysts


  • Homogeneous
  • Heterogeneous
• Catalytic converters


  • Made from rhodium, palladium, platinum
  • Have honeycomb structure to increase surface area
• Measure effect of concentration/temperature


  On rate of reaction using sodium thiosulfate + HCl
• Catalytic converters convert pollutants from car gas fumes into less harmful substances like N2, CO2, H2O
• Problems with catalytic converters: need to be replaced every 50,000 miles due to issues like cloudiness, sulfur, and high temperature