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Chemical Equations

Chemical Equations. Ch.9. (9-1) Chemical Rxn. Substances changed into something different Reactants  Products Same type & # of atoms on each side, just rearranged differently. Evidence of Chemical Change. Heat, light, or sound Gas Precipitate (ppt) Color change. Physical Change.

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Chemical Equations

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  1. Chemical Equations Ch.9

  2. (9-1) Chemical Rxn • Substances changed into something different • Reactants  Products • Same type & # of atoms on each side, just rearranged differently

  3. Evidence of Chemical Change • Heat, light, or sound • Gas • Precipitate (ppt) • Color change

  4. Physical Change • Same composition before & after rxn • Ex: melting, boiling H2O(s) H2O(l)

  5. Energy • Chemical rxns absorb or release E • Exothermic: release E • Reactants  Products + E • Endothermic: absorb E • Reactants + E  Products

  6. Activation E • Particles must collide for a chemical rxn to occur & enough E must be present • Spontaneous rxn: occurs naturally w/out extra E • Nonspontaneous: needs more E to start

  7. (9-2) Chemical Equations • Describes type & # of atoms that are rearranged during a rxn • Word eq.: • Ethanol + oxygen  carbon dioxide + water • Formula eq.: • C2H5OH + O2 CO2 + H2O

  8. Coefficients 2 K + Cl2 2 KCl • 2 K tells how many atoms react • The 2 applies to everything that follows it • 2 KCl = 2 K & 2 Cl • If the coef. is followed by a subscript they are multiplied • 2 H2O = 4 H & 2 O

  9. Subscripts & Superscripts 2 K + Cl2 2 KCl • Cl2 refers to 2 atoms of Cl • Diatomics: BrINClHOF CaCl2 Ca2+ + 2 Cl- • Ca2+ tells the charge of an ion

  10. Tips for Balancing Rxns • Save H & O for last • Treat polyatomic ions as a single element if on both sides of rxn • H2SO4 + Al  Al2(SO4)3 + H2 • 1 sulfate 3 sulfates • Balance left to right

  11. Tips for Balancing Rxns 4. Balancing 1 element may unbalance others 5. If present, make sure charges balance on each side of eq. • HCl + H2O  Cl- + H3O+ Net = 0 Net = 0 • Ag+ + Cu  Cu2+ + Ag 2Ag+ + Cu  Cu2+ + 2Ag Net = 2+ Net = 2+

  12. (9-3) States • C6H12O6(aq)+ 6O2(g) 6CO2(g)+ 6H2O(l)+ E

  13. Conditions • Conditions: • Yield:  • Equilibrium: • Heat: • Temp./Pressure: • Catalyst: heat .. 1 atm 0ºC Pd

  14. Equation Info • Balanced eq. show proportions • C6H12O6 + 6O2 6CO2 + 6H2O 1 mol 6 mol 6 mol 6 mol

  15. Mole Ratio • Conversion factor used to convert from 1 type of mole to another • Compare coef. C6H12O6 + 6O2 6CO2 + 6H2O 1 mol C6H12O6 : 6 mol CO2 3 mol C6H12O6 x 6 mol CO2 = 18 mol CO2 1 mol C6H12O6 Mole Ratio

  16. Mole Ratio Practice Determine the # of moles of each product would be formed given 16.0 mol KClO3 2 KClO3 2 KCl + 3O2 + 78 kJ • List the known 16.0 mol KClO3

  17. Mole Ratio Practice • Multiply by the mole ratio (moles that need to cancel on the bottom) 16.0 mol KClO3 x 2 mol KCl = 16 mol KCl 2 mol KClO3 16.0 mol KClO3 x 3 mol O2 = 24 mol O2 2 mol KClO3

  18. Mole Ratio Practice • Now calculate how much E was given off in kJ 16.0 mol KClO3 x 78 kJ = 624 kJ 2 mol KClO3

  19. Enthalpy • ∆H: total E of a system (absorbed or released) • Measured in Joules (J) • Exo: - ∆H • Stonger bonds produced • Endo: + ∆H • E added to break bonds

  20. Exo: Endo:

  21. (9-4) Types of Reactions • Combustion • Oxidation • Synthesis • Decomposition • Displacement (Single Replacement) • Double Displacement (Double Replacement)

  22. Combustion • Violently exo. rxn, usually w/ O2 • Produces CO2 & H2O • CH4 + 2O2 CO2 + 2H2O + 803 kJ

  23. Oxidation • Not as dramatic as combustion, but still involves O2 • Ex: rusting of iron 4Fe + 3O2 2Fe2O3

  24. Synthesis • Atoms or molecules combine to form a more complex cmpd • A + B  AB • 8 Fe + S8  8 FeS

  25. Polymerization • Series of synthesis rxns to make a very large molecule (polymer) High Density Polyethylene

  26. Decomposition • Single cmpd is broken down to produce 2 or more simpler substances • AB  A + B • 2 H2O  2 H2 + O2

  27. Displacement • Element replaces another element in a cmpd • AB + C  A + BC • 2Al + 3CuCl2 2AlCl3 + 3Cu

  28. Activity Series • Order of elements tendency to react w/ H2O & acids • Displace those below it (less active), but not above (more active) • Farther away = quicker rxns • 2K + MgO  K2O + Mg more less active active

  29. Displacement Practice • Mg + CuO  MgO + Cu • More reactive Mg displaces the less reactive Cu • Sn + CaO  SnO + Ca • No rxn! • Sn is less reactive than Ca

  30. Double Displacement • Ions from 2 cmpds interact in soln to form a product • AB + CD  AD + CB • 2KI + Pb(NO3)2 PbI2 + 2KNO3

  31. Rxn Classification Practice 1.  NaOH + KNO3 NaNO3 + KOH • Double displacement 2.  2 C4H10 + O2 8 CO2 + 10 H2O • Combustion 3.  2 Fe + 6 NaBr  2 FeBr3 + 6 Na • Single displacement

  32. Rxn Classification Practice 4.  CaSO4 + Mg(OH)2 Ca(OH)2 + MgSO4 • Double displacement 5.  Pb + O2 PbO2 • Synthesis 6.  Na2CO3 Na2O + CO2 • Decomposition

  33. Solubility Rules • Explain which substances dissolve & which form precipitates (ppt.) • Table 13-2, p.492 • Soluble = dissolves (aq) • Insoluble = ppt (s)

  34. NO3- NaNO3 = aq KNO3 = aq AgCl = s ZnCl2 = aq All nitrates are soluble.  Cl- All chlorides are soluble except AgCl, Hg2Cl2, and PbCl2.  Solubility Practice

  35. Ionic Equation • 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq) • Total Ionic Eq.: 2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq) • Spectator ion: ion that remains unchanged • K+, NO3-

  36. Net Ionic Equation • Includes only those cmpds that are involved in a chemical change • Omit spectators • 2I-(aq) + Pb2+(aq)  PbI2(s)

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