Lecture 18.1- Rate Factors


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Section 18.1 lecture for Honors & Prep Chemistry

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Lecture 18.1- Rate Factors

  1. 1. EXOTHERMIC REACTIONS CAN HURT! Which would you rather be near? ΔH for Rusting -822 kJ/mol ΔH for H2 explosion -483.6 kJ/mol
  2. 2. EXOTHERMIC REACTIONS CAN HURT! Which would you rather be near? ΔH for Rusting -822 kJ/mol ΔH for H2 explosion -483.6 kJ/mol
  3. 3. REACTION RATES HOW FAST? VERY ΔH for Rusting -822 kJ/mol slow ΔH for H2 explosion -483.6 kJ/mol VERY fast
  4. 4. Chemical rates are expressed as Increase in products/time or Decrease in reactants/time
  5. 5. A rate measures a change that occurs over time.
  6. 6. Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.
  7. 7. According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, IF the colliding particles have enough kinetic energy.
  8. 8. Effective Collision
  9. 9. Ineffective Collision
  10. 10. The minimum energy that colliding particles must have in order to react is called the activation energy.
  11. 11. The activated complex or transition state is the unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier.
  12. 12. ENDOTHERMIC EXOTHERMIC Much bigger activation energy! High activation energy = slower rate Low activation energy = faster rate
  13. 13. A tiny spark will provide the activation energy needed to react a few molecules of gas. The exothermic reaction of these few molecules will release enough energy to react the rest of the gas tank. BOOM!
  14. 14. Activation Energy Video
  15. 15. The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst.
  16. 16. Temperature – INCREASE TEMP, INCREASE RATE Faster particles collide more often and with more force, so they are more likely to get over the ACTIVATION ENERGY BARRIER.
  17. 17. Temperature – INCREASE TEMP, INCREASE RATE Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action.
  18. 18. Concentration- Increase reactant concentration, increase rate Crowded reactant particles collide more often.
  19. 19. Concentration- Increase reactant concentration, increase rate a. In air, a lighted splint glows and soon goes out. b. When placed in pure oxygen (higher oxygen concentration), the splint bursts into flame.
  20. 20. Particle Size MORE SURFACE AREA, FASTER RATE More particles are exposed, so more collisions are possible
  21. 21. The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive, destroying the grain elevator.
  22. 22. Catalysts ADD CATALYST, INCREASE RATE A catalyst lowers the activation energy barrier, so it is easier to get over!
  23. 23. A catalyst increases reaction rate, but it is not changed during the reaction. It is there at the beginning… … and it is still there at the end.
  24. 24. An enzyme is a biological catalyst
  25. 25. An inhibitor is a substance that interferes with the action of a catalyst. Antioxidants and antimicrobials used in drying fruits and preserving fruit juices slow the action of microbes and limit contact with air.
  26. 26. 18.1 Section Quiz. 1. The units below that would be appropriate to measure the rate of a chemical reaction is a. mmol/s. b. mol/L. c. kJ/mol. d. h/mol.
  27. 27. 18.1 Section Quiz. 2. In a chemical reaction, the energy of reactants is always a. greater than the energy of the products. b. more than the activation energy. c. less than the activation energy. d. less than the energy of the products.
  28. 28. 18.1 Section Quiz. 3. An increase in which one of the following will NOT increase the reaction rate? a. temperature b. concentration of reactants c. volume of gaseous reactants d. surface area of reactants
  29. 29. 18.1 Section Quiz. 4. A catalyst works because it a. lowers the activation energy. b. increases the temperature. c. is permanently changed in a reaction. d. supplies energy to a reaction.