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CHEMICAL EQUATIONS

CHEMICAL EQUATIONS. Water and what is known from its equation. *** Note that molecules and moles always have the SAME RATIOS. CHEMICAL REACTIONS. one or more substances are changed into different substances Represented by chemical equations 2H 2 (g) + O 2 (g)  2H 2 O(g)

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CHEMICAL EQUATIONS

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  1. CHEMICAL EQUATIONS

  2. Water and what is known from its equation. *** Note that molecules and moles always have the SAME RATIOS

  3. CHEMICAL REACTIONS • one or more substances are changed into different substances • Represented by chemical equations • 2H2 (g) + O2(g)  2H2O(g) • REACTANTS PRODUCTS

  4. CHEMICAL EQUATIONS • Show the substances undergoing change and the result(s). • Show relative amts. of elements/cmpds. that take part in the changes [coefficients] • See ‘Symbols Used in Chem. Rxn. handout

  5. 11.1 Writing Chemical Equations

  6. 11.1 Writing Chemical Equations • iron + oxygen  iron(III) oxide

  7. 11.1 Writing Chemical Equations • Hydrogen Peroxide  Water and Oxygen

  8. The PVC Method to WRITING A BALANCED CHEMICAL EQUATION • Pair the elements properly • Valences give subscripts • Coefficients balance the equation

  9. WRITING A BALANCED CHEMICAL EQUATION • Tips: • Start with element that appears only once on each side. • Save oxygen and hydrogen for last

  10. Lithium aluminum hydride reacts with water to produce lithium hydroxide, aluminum hydroxide and hydrogen gas. • LiAlH4 + H2O LiOH + Al(OH)3 + H2 • LiAlH4 + 4H2O LiOH + Al(OH)3 + H2 • LiAlH4 + 4H2O LiOH + Al(OH)3 + 4H2 • *Note that hydrogen is diatomic when not bonded to other elements.

  11. Diatomic Molecules H. BrOFINCl Harvey BrOFINCl

  12. Persistent difficulty ? • Check all FORMULAS to make sure they are correct • K2(SO4) v K2(SO3)

  13. Ammonia reacts with oxygen gas to produce nitrogen dioxide and water. • NH3 + O2 NO2 + H2O • 2NH3 + O2 NO2 + 3H2O • 2NH3 + O22NO2 + 3H2O • 2NH3 + 7/2O22NO2 + 3H2O • 4NH3 + 7O24NO2 + 6H2O

  14. Synthesis

  15. Common Types of Chemical Reactions Synthesis • two or more simple compounds combine to form a more complicated one • General form : A + B ---> AB • Iron and sulfur to form iron (II) sulfide: 8 Fe + S8 ---> 8 FeS

  16. Decomposition

  17. Common Types of Chemical Reactions Decomposition • opposite of a synthesis reaction • complex molecule breaks down to make simpler ones • General form: AB ---> A + B • Hydrogen peroxide decomposes to water and oxygen gas: H2O2 H2O +O2

  18. Single Replacement

  19. Common Types of Chemical Reactions Single Replacement • one element trades places with another element in a compound • General form: A++ BC ---> AC + B, or A- + BC ---> BA + C • Zinc replaces copper in copper sulfide solution: Zn +CuSO4  ZnSO4 + Cu

  20. Double Replacement

  21. Common Types of Chemical Reactions Double Replacement • cations (positive ions) of two different molecules switch places, forming two entirely different compounds • General form: AB + CD ---> AD + CB • Sodium Chloride (salt) solution reacts with silver nitrate to produce silver chloride and sodium nitrate. NaCl +AgNO3  AgCl + NaNO3

  22. Common Types of Chemical Reactions Combustion • oxygen combines with a compound containing carbon, hydrogen and sometimes oxygen • forms water and carbon dioxide. • General Form: CxHy CO2 + H2O • Exothermic • Burning of naphthalene: C10H8 + 12 O2 ---> 10 CO2 + 4 H2O

  23. Review and Foreshadow • Video • Logic and rules for balancing chemical equations are reviewed • Types of chemical reactions are introduced • Take Notes • Quiz (10 points) @ end of video • Name • Period • Number 1-10

  24. Decomposition: Special Cases • Anions and cations do not separate as expected. • X = any metal

  25. Metal carbonates • XCO3  XO + CO2 • metal oxide & carbon dioxide • CaCO3CaO + CO2

  26. Metal hydroxides • XOH  XO + H2O • metal oxide & water • Ca(OH)2CaO + H2O

  27. Metal chlorates • XClO3XCl + O2 • metal chloride & oxygen gas • Ca(ClO3)2 CaCl2 + 3O2

  28. Single Replacement Reactions • A++ BC ---> AC + B, or • A- + BC ---> BA + C • Are the free elements always able to replace the element in the compound? • How can we tell when / if the free elements will successfully replace the element in the compound?

  29. Activity Series [partial listing]

  30. Will these reactions occur? • ZnCO3 + H2? • ZnCO3 + H2N.R. • AgCl + Mg ? • 2AgCl + Mg MgCl2 + 2Ag

  31. Replacing HYDROGEN in WATER • Water is unusually stable. • Replacing the hydrogen in water depends on: • Placement of free element on activity series, and • TEMPERATURE

  32. Replacing HYDROGEN in WATER • < 175 oC • X + H2O  XOH + H2 • Metal hydroxide hydrogen gas • Ca + 2H2O  Ca(OH)2 + H2 • > 175oC • X + H2O  XO + H2 • Metal oxide hydrogen gas • Ca + H2O CaO + H2

  33. Double Replacement Reactions • AB + CD ---> AD + CB • When a double replacement reaction occurs one of the following are produced: • gas • precipitate • an insoluble solid that forms when two liquids are mixed • water • These rxn also called acid-base rxn

  34. SOLUBILITY • The property of a substance to dissolve • Water • Universal solvent • Solubility Table - handout • NaCl + AgNO3 NaNO3 + AgCl • 2NaCl + Fe(NO3)2 2NaNO3 + FeCl2 •  NR (no double replacement products made)

  35. Predicting Reaction Products • Analyze the reactants. • Decide what pattern of chemical reaction the reactants will fit. • Na and H2SO4 • a single element and a compound fit the single replacement pattern. • H2 and O2 • two elements fit the synthesis pattern.

  36. Use the pattern to decide which elements will go together. • [REMEMBER to refer to the Activity Series for single replacement reactions.] • Na + H2SO4 → • Na replaces H [Na stronger than H]; H becomes lone element. • 2Na + H2SO4 → Na2SO4 + H2

  37. Use valences to form good chemical formulas to represent the products. • The sum of the valences equals zero in a chemical formula. • Na+1; SO4-2 • 2Na + H2SO4 → Na2SO4 + H2 • Write the diatomic elements as H2, Br2, O2, F2, I2, N2, and Cl2. when they are by themselves.. (Henry BrOFINCl) • 2H2 + O2 → 2H2O

  38. Balance the equations using coefficients (BIG numbers placed in FRONT of the chemical formula.) • 2Na + H2SO4 → Na2SO4 + H2 • 2H2 + O2 → 2H2O • Balance H, Olast.

  39. Nuclear Equations • Nuclear equations result in the change of one element into another transmutation • 238 number of protons + neutrons 92 U number of protons (determines identity of atom)

  40. α particle decay • 238234 4 92 U 90 Th + 2He • thorium α particle

  41. β particle decay • 234 234 0 90 Th 91 Pa + -1e- • protactinium β particle • Decay continues until a stable substance is reached.

  42. K capture decay • 100 0 100 46 Pd + -1e- 45 Rh

  43. Rules for balancing nuclear equations • The sum of the mass numbers (top) is the same on both sides of the equation. • The sum of the electric charges (bottom) is the same on both sides of the equation.

  44. Find the unknown product • 18 0 9F  +1 e- + ? • Find the mass • 18 = 0 + x • 18 = x • 18 0 18 9 F  + 1e- + ?

  45. 230?V X • Find the charge • 9 = 1 + x • 8 = x • 18 0 18 9F  +1e- + 8 ?

  46. Find the element • 18 0 18 9F +1e- + 8O

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