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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] • Shift:  • Result: [NH3] ; [H2]

  14. Ex. 2 …concentration “stress”: • Given: N2 + 3H2 2NH3 • Stress: [H2] • Shift:  • Result: [NH3] ; [N2]

  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: pressure • Shift:  • Result: [NH3] ; [H2]

  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: Temp • Shift:  • Result: [N2] ; [H2]; [NH3]

  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

  27. Try another! • Pb + 2AgNO3 Pb(NO3)2 + 2Ag

  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 7. pH Scale 8. Indicators 1. releases H+ 2. releases OH- or accepts accepts H+ 3. H3O+ 4. OH- 5. Look like each other except for an H 6. DR Rx Acid + Base  Salt + Water 7. Scale: Acid – Neutral - Base 8. Chemicals that change color depending on acid or base environment. TABLE M

  47. 9. Dissociation 10. Electrolytes 11. Metal + Acid  ? 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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