chem

• Collision Theory


  States that the rate of a chemical reaction is proportional to the number of collisions between reactant molecules
• Effective Collisions


  • Collisions that result in a chemical reaction and a new product was formed
• Ineffective Collisions


  • Collisions where molecules strike with a different orientation and then they just bounce off each other without reacting
• When the concentration of reactants is doubled


  The frequency of collisions between them is doubled
• Reactant particles must possess a minimum amount of energy in order to produce effective collisions
• The larger the sample, the greater the number of effective collisions and the faster the rate of reactions
• The number of particles having enough energy is dependent on the temperature of the reactants
• Some reactions require the reactant particles to be in their particular orientation to produce an effective collision
• Effective Collisions


  • Ozone molecule (O3) must collide with nitrogen monoxide molecule (NO) where the nitrogen atom of NO must hit one of the oxygen atoms of the O3 molecule
• Ineffective Collisions


  • Molecules strike with a different orientation and then they just bounce off each other without reacting
• Requirements for an effective collision


  • Sufficient energy (kinetic energy) to break chemical bonds
  • Proper orientation of reactant particles
  • Frequency of collisions between reactants
• Decreasing reaction rate by lowering temperature can be significant
• Catalyst is a substance that helps speed up the rate of chemical reactions
• Catalysis


  The process of speeding up a reaction by using a catalyst
• Types of solid catalysts


  • Metallic elements (metals, oxides, sulfides, halides)
  • Semi-metallic elements (boron, aluminum, silicon)
• Gaseous and liquid catalysts

  Used in their pure form or in combination with suitable carriers or solvents
• Solid catalysts


  Commonly dispersed in other substances known as catalyst supports
• Catalytic action is a chemical reaction between the catalyst and the reactant, it forms chemical reactions that are able and ready to react with one another to form a product
• The catalyst is regenerated during the reaction
• Modes of reactions in solid catalysts


  • Acid-base
  • Oxidation-reductions
  • Formation of coordination complexes
  • Formation of free radicals
• Catalytic processes and their catalysts


  • Ammonia synthesis - iron
  • Sulfuric acid manufacture - nitrogen(II) oxide, platinum
  • Cracking of petroleum - zeolites
  • Hydrogenation of unsaturated hydrocarbons - nickel, platinum, or palladium
  • Oxidation of hydrocarbons in automobile exhausts - copper(II) oxide, vanadium(V) oxide, platinum, palladium
  • Isomerization of n-butane to isobutane - aluminum chloride, hydrogen chloride
• Homogeneous catalyst


  Catalyst and the reactants are in the same physical state or phase
• Examples of homogeneous catalysis

  • Conversion of oxygen gas to ozone - oxygen radicals (O-) as intermediates, ultraviolet light as catalyst
  • Conversion of persulphate and iodide ions to sulfate ion and iodine - iron ions as catalyst
• Heterogeneous catalyst


  Catalyst and the reactant are in different phases
• Zeolites


  Crystalline solid made up of repeating units of SiO4, an important class of heterogeneous catalyst
• Enzymes


  Natural catalysts found in the body, responsible for many essential biochemical reactions
• Homogeneous catalysis


  When the catalyst and the reactant are in the same phase
• Heterogeneous catalysis


  When the catalyst and the reactant are in different phases
• Common heterogeneous catalysts


  • Inorganic or non-carbon-containing solids
  • Elemental metals
  • Sulfides
  • Metallic salts
• Zeolites


  • Crystalline solid made up of repeating units of SiO4
  • Four joined SiO4 molecules form different ring and cage structures
  • Aluminum atom creates charge imbalance, offset by a proton
• Enzymes


  • Proteins that function as catalysts in living systems
  • Natural catalysts found in the body
  • Responsible for many essential biochemical reactions
  • Have substrate binding sites or active sites where molecules involved in a reaction become attached
• Amino acids


  • Building blocks of proteins
  • Uneven charge distribution from one end to the other
  • Main reason why enzymes possess catalytic capabilities
• Most enzymes lower the activation energy of chemical reactions
• Enzymes bind to reactants, changing their shape to destabilize the reactant and make it more susceptible to chemical changes
• Catalysts lower the energy required for the transition state of a reaction to be reached, allowing more molecular interactions
• Catalysts do not affect the degree or progress of a reaction, only the reaction kinetics
• Activation energy (Ea)


  The energy level that reactant molecules must overcome before a reaction can occur
• Catalysts increase reaction rates by providing a new mechanism with a smaller activation energy
• Flour is almost completely starch (carbohydrate) which burns like sugar
• Flour particles suspended in air have a large surface area exposed to oxygen per unit weight, making them dangerous and explosive