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Intro to Reactions

Ch. 9 – Chemical Reactions. Intro to Reactions. BACKGROUND. chemical reaction : process in which 1 or more substances are changed into 1 or more different substances.

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Intro to Reactions

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  1. Ch. 9 – Chemical Reactions Intro to Reactions

  2. BACKGROUND • chemical reaction: process in which 1 or more substances are changed into 1 or more different substances. • chemical equation: uses symbols and formulas to represent the identities and relative amounts of reactants and products in a chemical reaction

  3. A.Signs of a Chemical Reaction • Evolution of heat and light • Formation of a gas • Formation of a precipitate • precipitate: solid produced as result of chemical rxn in a soln. and separates from the soln. • Color change

  4. CHEMICAL EQUATIONS • Three requirements for chemical equations: • a. Equation must represent known facts: actual compounds and actual lab results

  5. CHEMICAL EQUATIONS • b. The equation must contain correct formulas for reactants and products • ex: diatomic elements (7) H2, N2, O2, F2, Cl2, Br2, I2

  6. CHEMICAL REACTIONS c. Law of Conservation of Mass must be satisfied • mass is neither created nor destroyed in a chemical reaction • total mass stays the same • atoms can only rearrange 4 H 2 O 4 H 2 O 36 g 4 g 32 g

  7. C. Chemical Equations A+B  C+D PRODUCTS REACTANTS • word equation: (def)reactants and products represented by words • hydrogen + oxygen  water • formula equation: (def)represents reactants and products of a chemical equation by their symbols or formulas • 2H2 + O2 2H2O

  8. symbols in chemical equations

  9. symbols in chemical equations

  10. Reversible Reaction • reversible reaction: the products re-form the original reactants Reversible Reaction Oscillating Reaction

  11. Significance of Chemical Eqn. • Coefficients show relative amounts of reactants and products 2H2 + O2 2H2O 2 molecule H2: 1 molecule O2: 2 molecules H2O

  12. Significance of Chemical Eqn. • Relative amounts of reactants and products can be determined from reaction coefficients. H2 + Cl2 2HCl 1 molecule H2: 1 molecule Cl2: 2 molecules HCl 1 mol H2: 1 mol Cl2: 2 mol HCl 2.02 g H2: 70.9 g Cl2: 72.92 g HCl

  13. Ch. 8 – Chemical Reactions II. Balancing Equations(p. 250-254)

  14. A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!

  15. B. Helpful Tips • Balance one element at a time. • Update ALL atom counts after adding a coefficient. • If an element appears more than once per side, balance it last. • Balance polyatomic ions as single units. • “1 SO4” instead of “1 S” and “4 O”

  16. C. Balancing Example Al + CuCl2 Cu + AlCl3 Al Cu Cl Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 3 3 2  2  6 1 1 1 1 2 3 2  3  6   3

  17. Chemical Reactions II. Balancing Equations

  18. A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!

  19. B. Helpful Tips • Balance one element at a time. • Update ALL atom counts after adding a coefficient. • If an element appears more than once per side, balance it last. • Balance polyatomic ions as single units. • “1 SO4” instead of “1 S” and “4 O”

  20. C. Balancing Example Al + CuCl2 Cu + AlCl3 Al Cu Cl Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 3 3 2  2  6 1 1 1 1 2 3 2  3  6   3

  21. Ch. 9 – Chemical Reactions III. Types of Chemical Reactions

  22. Synthesis A + B  AB • the combination of 2 or more substances to form a compound • only one product

  23. Synthesis H2(g) + Cl2(g)  2 HCl(g)

  24. Synthesis • Products: • ionic - cancel charges • covalent - hard to tell Al(s)+ Cl2(g)  AlCl3(s) 2 3 2

  25. Synthesis • Reactions with oxides • Oxides of active metals react with water to form metal hydroxides • Active metal: Ca metal oxide: CaO reaction: CaO + H2O  Ca(OH)2

  26. Synthesis • Examples: • Mg + O2 → • S8 + O2 → • Co + F2 → • BaO + H2O → MgO 2 2 8 SO2 8 2 2 CoF3 3 Ba(OH)2

  27. Decomposition AB  A + B • a compound breaks down into 2 or more simpler substances • only one reactant

  28. Decomposition 2 H2O(l)  2 H2(g) + O2(g)

  29. Decomposition • Products: • binary - break into elements • ((others - hard to tell – various rules)) KBr(l)  K(s) + Br2(l) 2 2

  30. Decomposition • Products for metal carbonates • MCO3  metal oxide + CO2 • CaCO3  CaO + CO2 • Products for metal hydroxides • NOT GROUP 1 METALS • M(OH)x metal oxide + water • Ca(OH)2 CaO + H2O

  31. Decomposition • Products for metal chlorates • MClO3  metal chloride + O2 • KClO3  KCl + O2 • Products for acids • acid  nonmetal oxide + water (generally) • H2SO4 SO3 + H2O 2 3 2

  32. Single Replacement A + BC  B + AC • one element replaces another similar element in a compound • metal replaces metal • nonmetal replaces nonmetal

  33. Single Replacement Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

  34. Single Replacement • Activity Series: Part of series Li > Rb > K > Ba > Sr > Ca > Na An element can only replace another if the free element is more reactive than the element in the compound Li + KCl  K + LiCl  LiCl + K NR (no reaction)

  35. Single Replacement • Replacement of metal by metal • Fe2O3+ AlAl2O3+Fe • Replacement of H in water by a metal • Na + H2O  NaOH + H2 • metal + water  metal hydroxide + hydrogen 2 2 2 2 2

  36. Single Replacement • Replacement of hydrogen in an acid by a metal • active metal + acid  metal compound + hydrogen • Mg + HCl  MgCl2 + H2 • Replacement of halogens • Cl2 + NaBr  NaCl + Br2 2 2 2

  37. Double Replacement AB + CD  AD + CB • ions in two compounds “change partners” • cation of one compound combines with anion of the other

  38. Double Replacement Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

  39. E. Double Replacement • Formation of a precipitate • 2 aqueous compounds form insoluble solid • 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq) • Formation of a gas • 1 product bubbles out of solution • FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)

  40. Double Replacement • Formation of water • HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

  41. Combustion A + O2 B • the burning of any substance in O2 to produce heat CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

  42. Combustion • Products: • contain oxygen • hydrocarbons form CO2 + H2O Na(s)+ O2(g)  Na2O(s) 4 2 C3H8(g)+ O2(g)  CO2(g)+ H2O(g) 5 3 4

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