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Topic 8: Kinetics and Equilibrium

Topic 8: Kinetics and Equilibrium. Kinetics = study of factors that make reactions speed up or slow down. 5/16/06. The KEY to kinetics is… . Collision Theory 1. Reaction requires A COLLISION between the particles.

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Topic 8: Kinetics and Equilibrium

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  1. Topic 8:Kinetics and Equilibrium Kinetics = study of factors that make reactions speed up or slow down. 5/16/06

  2. The KEY to kinetics is… • Collision Theory • 1. Reaction requires A COLLISION between the particles. • 2. Collision that cause a reaction is called AN EFFECTIVE COLLISION. • 3. EFFECTIVE COLLISION = A. Sufficient Energy B. Proper Orientation Ex. “the Home Run Swing”

  3. FACTORS THAT AFFECT THE RATE (speed) OF A REACTION: • 1. Nature of the reactants • 2. Concentration because more collisions (called…”collision frequency”.) • 3. Surface area because more collisions. • 4. Pressure (…if gas) because increases concentration and therefore collision frequency.

  4. 5. Presence of a catalyst because lowers Activation or start up Energy for the reaction. ex. The body’s enzymes • 6. Temperature because if T goes up then K.E. goes up; therefore each collision has more energy i.e. “has more punch”.

  5. Exothermic ReactionsPotential Energy Diagram:

  6. Ex. Exothermic P.E. Diagram

  7. Endothermic ReactionPotential Energy Diagram:

  8. Ex. Endothermic P.E. Diagram

  9. Exo versus Endo Reactions: • Energy “exiting” … so end up with less than you started. • R’s > P’s • H = - • Energy “entering”… so end up with more than you started. • R’s < P’s • H = +

  10. What does a catalyst do?A. Lowers Activation Energy!

  11. EQUILIBRIUM • Rate forward = Rate reverse • Must be REVERSIBLE REACTION • Does NOT mean Reactants = Products • Dynamic NOT static • Closed System

  12. Le Chatelier’s Principle: • “When a STRESS is placed on a system at equilibrium, the system will SHIFT in the direction that will relieve the stress.”

  13. Ex…of a Concentration “stress”: Given:N2 + 3H2 2NH3 Stress: [N2] increased! Shift: to relieve stress of the extra N2! Result: [NH3] up ; [H2] down.

  14. Ex. 2 …concentration “stress”: • Given: N2 + 3H2 2NH3 • Stress: [H2] goes down! • Shift:  to relieve stress of reduced amount of H2! • Result: [NH3] down ; [N2] up.

  15. Q. What do you do if “stress” is a pressure change? • A.Count the number of moles (i.e. the coefficients) on each side of the . Increased pressure favors the direction with less moles!

  16. Ex. …of a Pressure “stress”: Given:N2 + 3H2 2NH3 Stress: Increased Pressure! Shift:  to relieve the stress! Result: [NH3] up; [H2] down.

  17. Q. What do you do if the stress is a temperature change? • A. …look for exo and endo directions to the reaction. • An increase in temp causes endo direction to be favored since uses up the extra heat. • A decrease in temp causes exo direction to be favored since releases lost heat.

  18. Ex. …of temperature “stress”: Given:N2 + 3H2 2NH3 + kJ Stress: Increase in Temp! Shift:  to relieve the stress! Result: [N2] up; [H2] up; and [NH3] down!

  19. “The Common Ion Effect” • It’s really a Concentration “Stress”. • Ex. P.118, Q.27. CaSO4(s) Ca+2(aq) +SO4-2(aq) Na2SO4(s) 2Na+(aq) +SO4-2(aq) Common Ion is SO4-2! So…favors Reverse!

  20. ENTHALPY versus ENTROPY • Enthalpy = Heat Energy • Nature likes Low Energy . (…so prefers exo reactions). • Entropy = Randomness; “messy-ness” ex. (s) vs (g) or (s) vs (aq) • Nature likes High Entropy; Random; “Messy”.

  21. Topic 9: “REDOX” REACTIONS And ELECTROCHEMISTRY

  22. Q. WHAT IS AN OXIDATION NUMBER? OXIDATION = CHARGE NUMBER TOOLS = P.T. & Table E

  23. RULES FOR ASSIGNING OXIDATION NUMBERS: Atoms in the free state have Ox. No. of 0. Group 1’s = + 1 Group 2’s = + 2 Group 3’s = + 3 Group 17’s = - 1 O = - 2 (except peroxide, H2O2, then O = -1) H = + 1 (except with metal hydride, NaH; then H = -1) Rule: “The sum of all oxidation numbers is equal to the charge on the molecule (…0) or ion.”

  24. Ex. Determining Ox. No. • 1. KMnO4 • What is the ox. no. for Mn ? Ans. +7 • 2. PO4-3 • What is the ox. no. for P ? Ans. +5 • 3. CuSO4 • What is the ox. no. for S ? Ans. +6 ( Cu is +2 )

  25. What is meant by Oxidation and Reduction ? Oxidation means the charge on an element increases (i.e. more +)… b/c atom “loses” e-! Reduction means the charge is decreasing (i.e. more -)… b/c atom “gains” e-!

  26. Ox. No. changes during a Redox Reaction (usually SR reaction): Ex. Label the following Redox Rx: Zn + CuSO4 ZnSO4 + Cu Ox: Zn0  Zn+2 + 2e- Red: Cu+2 + 2e-  Cu0

  27. Try another! Pb + 2AgNO3 Pb(NO3)2 + 2Ag Ox: Pb0 Pb+2 + 2e- Red: Ag+1 + 1e-  Ag0

  28. Oxidation versus Reduction “OIL” = “Oxidation Is Loss of e-’s” Half-Reaction: Zn0 Zn +2 +2e- “RIG” = “Reduction Is Gain of e-’s” Half-Reaction: Cu+2 + 2e-  Cu0

  29. Do Now! Zn + CuSO4 ZnSO4 + Cu Half Reactions: Ox: Zn0  Zn+2 + 2 e- “oil” Red: Cu+2 + 2e-  Cu0 “rig”

  30. Schematic Drawing of anElectrochemical Cell (a battery):

  31. Electrodes: “An Ox and a Red Cat” Anode = The electrode where oxidation takes place; The higher one on Table J (usually left) Cathode = The electrode where reduction takes place; The lower one on Table J (usually on right)

  32. Remember: 1. Ox = charge increasing. Red = charge decreasing. 2. “OIL” = oxidation is losing e-’s. “RIG” = reduction is gaining e-’s. 3. “An…Ox” = Anode is site of oxidation. “Red…Cat” = Cathode is site of reduction. 4. Anode = Higher Metal on Table J !!! 5. e- flow is ALWAYS Anode  Cathode

  33. 6. Salt Bridge function = a. allows for the migration of ions; b. completes the circuit.

  34. Do Now! Given: a) Write the half-reactions; b) Balance; c) Label Anode & Cathode; d) e- source? Al + NiSO4 Al2(SO4)3 + Ni

  35. Ex. Voltaic Cell (Spontaneous electricity = a battery)

  36. Ex. Electrolytic Cell (Non-Spontaneous = Au or Ag plating)

  37. Another example of an Electrolytic Set up:

  38. SIMILARITIES betweenVoltaic and Electrolytic Cells: • Similarities: • Both are REDOX Rxs. • Both have ANODE as site of OXIDATION; CATHODE as site of REDUCTION. • e- flow is always Anode  Cathode.

  39. DIFFERENCES betweenVoltaic and Electrolytic Cells: VOLTAIC ELECTROLYTIC 1. Spontaneous 1. Non-spontaneous 2. Automatically 2. Requires a releases e-’s battery hook-up. i.e. electricity. 3. Anode = - 3. Anode = + Cathode = + Cathode = -

  40. Topic 10: Acids, Bases, & Salts

  41. Q. How can you recognize an acid or a base from its formula? Table L = Bases end with OH; or accept H! NaOH KOH Ca(OH)2 & NH3 Table K = Acids begin with H! HCl HNO3 H2SO4 H3PO4 H2CO3 & CH3COOH ?

  42. A Look At Acid and Base Ions: The Acid Ion: H+ + H2O  H3O+ Table E The Hydronium Ion The Base Ion: OH- Table E The Hydroxide Ion

  43. Conjugate Acid – Base Pairs: They look like each other except for an H. Ex 1. HCl + H2O  H3O+ + Cl- Ex 2. H2SO4 + H2O  H3O+ + HSO4-

  44. The Neutralization Reaction HCl + NaOH  HOH + NaCl Acid + Base  Water + Salt It’s a double replacement reaction! How about… Ca(OH)2 + H2SO4 ? CaSO4 + 2 H2O

  45. The pH Scale: 0 ------------ 7 ------------ 14 Acid Neutral Base Note: Each pH unit means a power of 10. Ex. pH 3  5; 2 units; 100X weaker acid.

  46. Do Now! …do you know the definition? 1. Acid 2. Base 3. Hydronium ion 4. Hydroxide ion 5. Conjugate Acid – Base Pairs 6. Neutralization Reaction 1. releases H+ 2. releases OH- or accepts H+ 3. H3O+ 4. OH- 5. Look like each other except for an H 6. DR Rx Acid + Base  Salt + Water

  47. 7. pH Scale 8. Indicators 9. Dissociation 10. Electrolytes 11. Metal + Acid  ? 7. Scale: Acid – Neutral – Base 8. Chemicals that change color depending on acid or base environment. TABLE M 9. Separation of ions 10. Solutions that conduct electricity; ions in it! 11. SR Rx liberating H2

  48. Indicators Chemical that changes color depending on whether in acid or base environment. Any explanation for how an indicator works? Table M Which indicator would be best for telling you when you are at NEUTRAL pH?

  49. If H+ attached from an acid, molecule reflects one color to your eye… • Red cabbage dye • Litmus • Phenolphthalein • If OH- attached from a base, molecule reflects a different color to your eye… • Red cabbage dye • Litmus • Phenolphthalein

  50. Some common indicators:

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