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Mastering Chemical Equations: Reactions and Synthesis Demystified

Understand chemical reactions like never before with balanced equations for synthesis, decomposition, and more. Learn the PVC method and tackle tricky scenarios like double replacement reactions. Get ready to ace your chemistry quizzes!

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Mastering Chemical Equations: Reactions and Synthesis Demystified

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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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