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EXAM 1 GRADES

EXAM 1 GRADES. Feb.19. Announcements. You can pick up your exams after class. You can see your make up exams in my office. Deadlines for HW2 and HW3 pushed till Sunday, Feb. 24 Call Aris if you have problems with HW. Most students finished it.

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EXAM 1 GRADES

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  1. EXAM 1 GRADES

  2. Feb.19. Announcements • You can pick up your exams after class. • You can see your make up exams in my office. • Deadlines for HW2 and HW3 pushed till Sunday, Feb. 24 • Call Aris if you have problems with HW. Most students finished it. • If you can not find your exam talk to me after class. • There have been changes to the “freshman forgiveness” policy. Consult your academic adviser if you plan to take advantage of it.

  3. 4.6. Redox reactions with chemical elements • If element reacts it forms a compound. This requires a change in the ON, thus it is a redox reaction. C+ O2 = CO2 • Not all redox reactions involve elements, but all reactions of the elements are redox. SO2 + MnO2 = SO3 + MnO

  4. Some rules for redox reactions • Metals tend to loose electrons, non-metal tend to gain electrons. • Non-metals with a higher group number tend to take electrons away from non-metals with a lower group number. • Non-metals with a lower period number tend to take electrons away from non-metals with a higher period number. • The rules for max and min oxidation number are the same as for max and min valency and for stable charge. • The strongest oxidizing agents are F2>O2>Cl2. • The strongest reducing agents are Cs>K>...>Li

  5. 4.6. Redox reactions with chemical elements • Combination X+Y= Z • Decomposition Z = X+Y • Displacement X+YZ = XZ + Y Metals usually are reducing agents, nonmetals are oxidizing.

  6. Combination 1. Metal and nonmetal form an ionic compound

  7. Combination 2. X+Y= ZTwo nonmetals form a covalent compound N2 (g) + 3H2 (g) = 2 NH3 (g) P4 (s) + 6Cl2 (g) = 4PCl3(l) C (s)+ O2 (g) = CO2 (g)

  8. Combination 2. X+Y= ZCompound combines with element • 2CO + O2 = CO2 • PCl3 +Cl2 = PCl5 • Zn + 2MnO2 = ZnMn2O4

  9. Decomposition 1. Thermal 2KClO3 (s) = 2KCl (s)+ 3O2 (g) H2O2 = H2O + ½ O2

  10. Decomposition 2. Electrolytic • H2O = H2 + 1/2O2 • 2HF = H2 + F2 • NaCl = Na +1/2 Cl2

  11. Displacement 1. An active metal displacing hydrogen from water or acid.

  12. Displacement 2. Displacing one metal with another.

  13. Li K Ba Ca Na can displace H from water strength as reducing agents H2 Cu Hg Ag Au cannot displace H from any source - Figure 4.20 The activity series of the metals. Mg Al Mn Zn Cr Fe Cd more metallic character means stronger reduction properties, easier to loose electrons. can displace H from steam + Co Ni Sn Pb can displace H from acid more positive metals displace more negative metals from their salts: Cu, Pb Hg, Fe +

  14. Displacement 3. Nonmetal exchange: stronger oxidants: F2 > Cl2> (O2) > Br2 > I2 2KBr + Cl2 = 2KCl +Br2 2H2O + 2F2 = 4HF + O2 burning water 4HI + O2 = 2I2 + 2H2O Br- and I- are stable in air. O2 displacement occurs only in acids.

  15. Combustion: any redox reaction that involves O2 as oxidant • 4HI + O2 = 2I2 + 2H2O displacement of nonmetal • 2CO + O2 = CO2 combination with compound • C (s)+ O2 (g) = CO2 (g) combination w nonmetal • C6H12O6 + 6O2 = 6CO2 + 6H2O neither biorespiration, energy source for living organisms

  16. (a) magnesium(s) + nitrogen(g) magnesium nitride (aq) (b) hydrogen peroxide(l) water(l) + oxygen gas (c) aluminum(s) + lead(II) nitrate(aq) aluminum nitrate(aq) + lead(s) Sample Problem 4.10 Identifying the Type of Redox Reaction PROBLEM: Classify each of the following redox reactions as a combination, decomposition, or displacement reaction, write a balanced molecular equation for each, as well as total and net ionic equations for part (c), and identify the oxidizing and reducing agents: PLAN: Combination reactions produce fewer products than reactants. Decomposition reactions produce more products than reactants. Displacement reactions have the same number of products and reactants.

  17. 0 0 +2 -3 Mg(s) + N2(g) Mg3N2 (aq) +1 -1 +1 -2 0 H2O2(l) H2O(l) + O2(g) 2 H2O2(l) 2 H2O(l) + O2(g) 0 +2 +5 -2 +3 +5 -2 0 Al(s) + Pb(NO3)2(aq) Al(NO3)3(aq) + Pb(s) 2Al(s) + 3Pb(NO3)2(aq) 2Al(NO3)3(aq) + 3Pb(s) Sample Problem 4.10 Identifying the Type of Redox Reaction (a) Combination continued 3 Mg is the reducing agent; N2 is the oxidizing agent. (b) Decomposition 1/2 or H2O2 is the oxidizing and reducing agent. (c) Displacement Pb(NO3)2 is the oxidizing and Al is the reducing agent.

  18. 4.7. Reversible Processes H2O (l) → H2O (g); evaporation H2O (g) → H2O (l); condensation H2O (l) ↔ H2O (g) NaCl (s) → Na+ (aq) + Cl- (aq) Na+ (aq) + Cl- (aq) → NaCl (s) NaCl (s) ↔ Na+ (aq) + Cl- (aq) chemical reactions are also reversible

  19. Phase Equilibrium

  20. Phase Equilibrium

  21. Phase Equilibrium Equilibrium is dynamic because processes are still occurring

  22. N2O4 (g) ↔ 2NO2 (g) colorless brown Dynamic Chemical Equilibrium

  23. N2O4 (g) ↔ 2NO2 (g) colorless brown Dynamic Chemical Equilibrium

  24. N2O4 (g) ↔ 2NO2 (g) colorless brown Dynamic Chemical Equilibrium

  25. N2O4 (g) 2NO2 (g) colorless brown Dynamic Chemical Equilibrium

  26. Dynamic Chemical Equilibrium • most reactions are reversible • products form • can react → reactants • equilibrium is reached when • rate of forward reaction • = rate of reverse reaction • amount of reactants do NOT equal amount of products

  27. equilibrium requires • a closed system • all substances in contact with each other • at equilibrium • rate of forward reaction = rate of reverse reaction • quantities of product and reactant remain unchanged • reactions still continue to occur; dynamic

  28. 2HI ↔ H2 + I2 • At what time does this system first reach equilibrium? • Is the system at equilibrium after 5 s?

  29. equilibrium may favor products Na2SO4(aq) + BaCl2(aq) → NaCl(aq) + BaSO4(s) precipitate forms – removes Ba2+ & SO42- ions reaction is largely complete equilibrium may favor reactants CH3COOH (aq) + H2O (l) ↔ CH3COO-(aq) + H3O+(aq) weak acid only dissociates partially larger quantity of reactants process is dynamic

  30. not all reactions go straight toward equilibrium • Living organisms are the best-known examples of lasting non-equilibrium systems with periodic behavior. • There is no magic “living spirit” responsible for such behavior of living systems. Artificial chemical mixtures can behave the same way. • Belousov-Zhabotinskiy reaction is an example of a non-equilibrium oscillating reaction.

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