Rates of reaction


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Rates of reaction

  1. 1. Factors Affecting Rate of Reaction The Collision Theory
  2. 2. The Collision Model <ul><li>A chemical reaction can only occur when molecules collide. </li></ul><ul><li>The chart below compares a car accident to the particle theory collision model. </li></ul>http:// www.yteach.co.uk/page.php/resources/view_all?id =collision_theory_molecule_potential_energy_diagram_reaction_mechanism_t&from=search http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_factor_collision_theory_temperature_concentration_reactant_pressure_page_1&from=search New products must be formed There must be proof of an accident (scratch, dent etc.) The collision must have enough energy to break apart the particles Cars must damage (something breaks) Reactant particles must collide Cars must collide Conditions for a successful chemical reaction Conditions for a car accident
  3. 3. Rate of Reaction <ul><li>Definition: </li></ul><ul><li>the speed at which reaction occurs </li></ul><ul><li>the amount of time it takes for a successful collision to be completed </li></ul>http:// phet.colorado.edu/new/simulations/index.php?cat =Chemistry http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=553
  4. 4. Rate of Reaction <ul><li>Factors Affecting the Rate of Reaction: </li></ul><ul><li>Temperature </li></ul><ul><li>Concentration </li></ul><ul><li>Pressure (Only for gases) </li></ul><ul><li>Surface area </li></ul><ul><li>Catalyst or Enzyme </li></ul>http:// phet.colorado.edu/new/simulations/index.php?cat =Chemistry http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=553
  5. 5. Factors Affecting the Rate of Reaction <ul><li>Temperature: Increasing the temperature of the reactants increases the rate of reaction. </li></ul><ul><li>Increasing the temperature </li></ul><ul><li>molecules move faster </li></ul><ul><li>More chance of collision and </li></ul><ul><li>Crash into each other with higher energy </li></ul>http://www.yteach.co.uk/page.php/resources/view_all?id=temperature_catalyst_reaction_rate_Maxwell_Boltzmann_molecular_energy_t&from=search
  6. 6. Factors Affecting the Rate of Reaction <ul><li>Temperature’s application to food preservation: </li></ul>
  7. 7. Factors Affecting the Rate of Reaction (Concentration) <ul><li>higher the concentration </li></ul><ul><li>more molecules in the same space </li></ul><ul><li>more chance of collision </li></ul><ul><li>faster the reaction </li></ul><ul><li>Pressure: The higher the pressure, the lower the volume for the same molecules, the more they collide and finally faster reaction. </li></ul>http:// www.yteach.co.uk/page.php/resources/view_all?id =rate_equation_reaction_concentration_kinetic_surface_area&from=search http://phet.colorado.edu/simulations/sims.php?sim=Gas_Properties http://www.yteach.co.uk/page.php/resources/view_all?id=rate_equation_reaction_concentration_kinetic_surface_area&from=search
  8. 8. Factors Affecting the Rate of Reaction <ul><li>Surface Area: increasing the surface area causes increase the rate of reaction. </li></ul><ul><li>More surface area </li></ul><ul><li>More molecules </li></ul><ul><li>available for collision </li></ul><ul><li>Increase the </li></ul><ul><li>number of collision </li></ul>http:// www.yteach.co.uk/page.php/resources/view_all?id =reaction_rate_factor_collision_theory_temperature_concentration_reactant_pressure_page_4&from=search http://www.yteach.co.uk/page.php/resources/view_all?id=rate_equation_reaction_concentration_kinetic_surface_area&from=search
  9. 9. Factors Affecting the Rate of Reaction <ul><li>Catalyst: </li></ul><ul><li>substances that can increase the rate of reaction by reducing the amount of energy required for a successful collision </li></ul><ul><li>provides sites for molecules to interact thus increasing the chance of collision (like a match maker) </li></ul>http://www.yteach.co.uk/page.php/resources/view_all?id=temperature_catalyst_reaction_rate_Maxwell_Boltzmann_molecular_energy&from=search
  10. 10. Factors Affecting the Rate of Reaction <ul><li>Characteristics of a catalyst: </li></ul><ul><li>Does not participate as a reactant. </li></ul><ul><li>Does not change during the reaction. </li></ul><ul><li>Is not consumed or used up. </li></ul><ul><li>Enzyme: a biological catalyst </li></ul>http://www.yteach.co.uk/page.php/resources/view_all?id=temperature_catalyst_reaction_rate_Maxwell_Boltzmann_molecular_energy&from=search
  11. 11. Application of Catalyst: Catalytic Converter <ul><li>A catalytic converter converts harmful pollutants into less harmful emissions before they ever leave the car's exhaust system. </li></ul>
  12. 12. Components of Car Emissions <ul><li>3 Unregulated Emmissions (safe and allowable) </li></ul><ul><li>Nitrogen gas (N2) </li></ul><ul><li>air is 78-percent nitrogen gas </li></ul><ul><li>most of this passes right through the car engine </li></ul><ul><li>Carbon dioxide (CO2) </li></ul><ul><li>product of complete combustion </li></ul><ul><li>contribute to global warming </li></ul><ul><li>Water vapor (H2O) </li></ul><ul><li>product of complete combustion </li></ul>
  13. 13. Components of Car emissions <ul><li>Regulated emissions (unsafe pollutants, monitored) </li></ul><ul><li>Nitrogen oxides (NO and NO2) </li></ul><ul><li>Product of oxidation </li></ul><ul><li>contributor to smog and acid rain </li></ul><ul><li>causes irritation to human mucus membranes </li></ul><ul><li>Carbon monoxide (CO) </li></ul><ul><li>Product of incomplete combustion </li></ul><ul><li>poisonous gas that is colorless and odorless </li></ul><ul><li>Hydrocarbons </li></ul><ul><li>Product of incomplete combustion </li></ul><ul><li>major component of smog produced mostly from evaporated, unburned fuel </li></ul>
  14. 14. Components of a Catalytic Converter <ul><li>Converting Nitrogen oxides (NO and NO2) </li></ul><ul><li>Reduction catalyst: platinum & rhodium </li></ul><ul><li>catalyst rips the nitrogen atom out of NO or NO2 and holds onto it </li></ul><ul><li>frees up oxygen in the form of O2 </li></ul><ul><li>nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2 </li></ul>2NO  N 2 + O 2 2NO 2  N 2 + 2O 2
  15. 15. Components of a Catalytic Converter <ul><li>Converting Carbon monoxide (CO) and hydrocarbons </li></ul><ul><li>Oxidation catalyst: platinum & palladium </li></ul><ul><li>catalyst helps burn the unburned CO and hydrocarbons with the remaining oxygen in the exhaust gas to produce the harmless carbon dioxide and water </li></ul>2CO + O 2  2CO 2 CxHy + O 2  CO 2 + H 2 O
  16. 16. Efficiency of Catalytic Converter <ul><li>Unfortunately these catalytic converters only works well when the engine is hot. </li></ul><ul><li>Video: NASA Low Temperature Catalytic Converter (Oxidation Catalysts) </li></ul><ul><li>http://www.youtube.com/watch?v=n0jieV9A1AU </li></ul>
  17. 17. Application of a fast reaction: Explosion <ul><li>Requirements of an explosion </li></ul><ul><li>(uncontrolled and controlled) </li></ul><ul><li>It must produce heat </li></ul><ul><li>It must produce gas </li></ul><ul><li>It must react quickly </li></ul><ul><li>In order to be useful, it has to happen in a controlled manner. </li></ul><ul><li>Video: Chemical Plant Explosion </li></ul><ul><li>http:// www.youtube.com/watch?v =_ KuGizBjDXo </li></ul>http://phet.colorado.edu/new/simulations/index.php?cat=Chemistry http:// www.explorelearning.com/index.cfm?method = cResource.dspView&ResourceID =553 http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_fast_slow_determination_kinetic_reactant_product_catalyst&from=search http:// www.yteach.co.uk/page.php/resources/view_all?id =reaction_rate_fast_slow_determination_kinetic_reactant_product_catalyst&from=search
  18. 18. Application of a fast reaction: Explosion in Air Bags <ul><li>sensors that detect a collision </li></ul><ul><li>send an electric signal that detonates an igniter compound </li></ul><ul><li>heat catalyzes the decomposition of the sodium azide (NaN3) generating nitrogen gas (N2) to fill the air bag </li></ul>
  19. 19. Application of a fast reaction: Explosion in Air Bags <ul><li>Air Bag Chemistry </li></ul><ul><li>NaN3 + heat  Na + N2 (g) </li></ul><ul><li>Nitrogen gas (N2) inflates the air bag. </li></ul>
  20. 20. Application of a fast reaction: Explosion in Air Bags <ul><li>Air Bag Chemistry: NaN3 + heat  Na + N2 (g) </li></ul><ul><li>Byproduct (Na) is highly reactive and potentially explosive so it needs to be stabilized: </li></ul><ul><li>Na + KNO3  Na2O + K2O + N2 (g) </li></ul><ul><li>(resulting metal oxides are still highly reactive) </li></ul><ul><li>  </li></ul><ul><li>Na2O + K2O + SiO2  alkaline silicate </li></ul><ul><li>(silicate glass is very stable) </li></ul>
  21. 21. Application of a fast reaction: Explosion in Air Bags <ul><li>Process only takes 30-40 milliseconds (0.03-0.04s) </li></ul><ul><li>the airbag must begin to deflate by the time the occupant hits it </li></ul><ul><li>It takes about 50 milliseconds for occupant to hit the airbag </li></ul><ul><li>air bag’s deflation absorbs the forward-moving energy of the occupant. </li></ul>Funny video: Old lady vs. young guy in car http:// www.youtube.com/watch?v =9bNYeJ-EDkc