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Chapters 13 & 14

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  1. Chapters 13 & 14 Kinetics and Equilibrium

  2. Chemical Kinetics • What is the study of chemical kinetics? • What is a reaction rate? • The speeds, or rates, at which chemical reactions take place • Change in a quantity over a certain time • Symbol: k

  3. Chemical Kinetics • What quantities can we easily measure changes over time? • Concentration [A] • Mass • Volume

  4. Chemical Kinetics • Why would we want to study this? • Manufacturing • Safety • Food preservation

  5. Graphical Representation • How do we represent this graphically?

  6. Collision Theory • What is the main concept behind collision theory? • Reactions can not occur if molecules do not collide • Manipulating variables that affect the number of collisions over a certain time

  7. Collision Theory • What is activation energy (Ea)? • Amount of energy required for a reaction to take place if the molecules are oriented correctly • Affected by temperature (KE)

  8. Maxwell Boltzmann Curve • What does a Maxwell Boltzmann curve represent? • The number of molecules that have the required activation energy to react • Shifts based on temperature

  9. Variables • What variables affect collisions that increase the reaction rate? • Size • b/c surface area increases • Temperature • Concentration • Pressure

  10. Catalysts • How does a catalyst affect activation energy? • How does a catalyst affect the rate of reaction? • Lowers the activation energy • It does NOT take part in the reaction in any way • Increases the reaction rate

  11. Variables and Catalysts

  12. Variables and Catalysts

  13. Variables and Catalysts

  14. Energy Profiles • What is an energy profile? • Shows the change in energy between the reactants and the products • Able to determine whether the reaction is endothermic or exothermic • Shows activation energy • Shows if a catalyst is present

  15. Energy Profiles

  16. Energy Profiles

  17. Energy Profiles Energy of the reactants Activation energy for the forward reaction Energy of the activated complex or transition state Activation energy for the reverse reaction Energy absorbed by the systemfrom the surroundings Energy of the products

  18. Energy Profiles • The energy of the reactants is 730 kJ and the energy of the products is 850 kJ. • What is the amount energy gained or released by the system? • 120 kJ (endothermic) • What number does that represent on the above diagram? • 5

  19. Energy Profiles and Catalysts • Which quantities are affected by the use of a catalyst? • I – Yes, less energy absorbed by the reactants • II – Yes, less energy released by the formation of the products • III – No, the overall change in energy is unaffected

  20. Energy Profiles

  21. Energy Profiles

  22. Chemical Equilibrium • What is a reversible reaction and how is it represented? • In a reversible reaction, what happens when equilibrium is reached? • A reaction where reactants create products and products create reactants • Amount of reactants and products remains constant

  23. Types of Equilibrium • What is the difference between a physical and chemical equilibrium? • Chemical involves two or more different substances • Physical involves the same substance changing phases

  24. Types of Equilibrium • What is the difference between a dynamic and static equilibrium? • Dynamic – the rate of the forward reaction and reverse reaction are equal and the reaction continues • Static – the forward and reverse reactions stop once equilibrium is reached

  25. Equilibrium Constant • What is an equilibrium constant? • How can it be calculated? • For a reversible reaction at equilibrium and constant temperature, the concentration ratio of products to reactants is constant • K or Keq or Kc

  26. K • How would you set up the calculation for K for the following reaction:

  27. K • What does K tell us about the reaction? • If K = 1 then it is in equilibrium • If K >>> 1 then… • Shift right • Favors products • Usually what you want! • If K <<< 1 then… • Shift left • Favors reactants

  28. Equilibrium Side Note • How does the term homogeneous equilibrium apply to reactions? • This means that all substances are in the same phase or state • Solid, liquid, gas or aqueous • NOTE: We will not be working with heterogeneous equilibriums

  29. Equilibrium Practice Pg. 566 Example 14.2

  30. Equilibrium Practice Pg. 566 Practice Exercise

  31. Equilibrium • What rule generally applies to equilibrium reactions? • What are the four stresses that you need to be familiar with? • Le Chatelier’s Principle • Concentration • Temperature • Pressure • Catalysts

  32. Concentration • How does concentration affect the equilibrium? • Adding more reactants • Shift to the right • Creates more product • Adding more products • Shift to the left • Creates more reactant

  33. Temperature • How does temperature affect the equilibrium? • Need to know whether the reaction is exothermic or endothermic • Exothermic – heat is a product, so adding more heat pushes the reaction left • Favors reactants • Endothermic – heat is a reactant so it pushes the reaction right • Favors products

  34. Pressure • How does pressure affect the equilibrium? • If pressure is added the equilibrium will shift toward the side with less volume • In this case, added pressure would mean that N2O4 would be favored

  35. Catalyst • How does the presence of a catalyst affect the equilibrium? • Will speed up the rate at which equilibrium is reached • Increases forward and reverse reaction rates • It has NO effect on the equilibrium or the value of K

  36. Equilibrium Practice 14.52

  37. Equilibrium Practice 14.56

  38. Equilibrium Practice 14.60

  39. Bohr-Haber Synthesis • Why is ammonia production important? • What is the balanced reaction? • Fertilizers • Explosives • Chemical Weapons

  40. Bohr-Haber Synthesis • How will you manipulate certain stresses to maximize output? • Pressure • High pressure favors the products because the volume ratio is 4:2 • Temperature • Exothermic reaction means lower temperatures favor production

  41. Bohr-Haber Synthesis • Why is a catalyst used in this reaction and does it affect the equilibrium? • Even though the yield of this experiment is only 15%, why is it still favorable to do? • Since lower temperatures slow the rate of production an iron catalyst is used, but it does not affect equilibrium • Recycling - Unused reactants are recycled back into the reaction to create more ammonia

  42. The contact Process • Why is the production of sulfuric acid important? • What is one of the first reactions in the creation of sulfuric acid? • Fertilizers • Paints • Detergents • Fiber production

  43. The contact Process

  44. The contact Process • How will you manipulate certain stresses to maximize output? • Pressure • High pressure favors the products because the volume ratio is 3:2 • Temperature • Exothermic reaction means lower temperatures favor production • A vanadium catalyst is used to increase the rate at which equilibrium is reached

  45. Article - The Nitrogen Fix The Nitrogen Fix: Breaking a Costly Addiction Over the last century, the intensive use of chemical fertilizers has saturated the Earth’s soils and waters with nitrogen. Now scientists are warning that we must move quickly to revolutionize agricultural systems and greatly reduce the amount of nitrogen we put into the planet's ecosystems. by Fred Pearce