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Predicting Reactions

Predicting Reactions. Presented by Mr. Mark Langella AP Chemistry Instructor College Board Consultant 2009. Why do the reactions occur?. Gibbs Free Energy drives the Spontaneous reactions Lower PE energy Formation of Stronger Bonds Greater Entropy ( Formation of Gases)

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Predicting Reactions

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  1. Predicting Reactions Presented by Mr. Mark Langella AP Chemistry Instructor College Board Consultant 2009

  2. Why do the reactions occur? • Gibbs Free Energy drives the Spontaneous reactions • Lower PE energy • Formation of Stronger Bonds • Greater Entropy ( Formation of Gases) • Solubility • Formation Constant

  3. Ways of Expressing CHEMICAL EQUATIONS • Word equation • In word equations, the names of the reactants and products are written out. The following example is a word equation: • carbon + oxygen carbon dioxide

  4. Formula equations • Formula equations consist of formulas substituted for the names in the word equation. The reaction above becomes • C + O2 CO2

  5. Ionic equations • In ionic equations, all water soluble compounds in an aqueous solution are separated into ions. • 2NaI(aq) + Pb(NO3)2(aq) 2NaNO3(aq) + PbI2(s) • 2Na+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) 2Na+(aq) + 2NO3-(aq) + PbI2(s) • Spectator ions - Spectator ions do not participate in the chemical reaction. That is, they are identical on both sides of the equation.

  6. Net ionic equations • The net ionic equation contains all of the particles in the ionic equation less any spectator ions. • 2Na+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) 2Na+(aq) + 2NO3-(aq) + PbI2(s) • Pb2+(aq) + 2I-(aq) PbI2(s)

  7. Balancing • We were reminded (especially by the combustion reaction above) that the coefficients used for balancing should be the lowest possibleWHOLE NUMBER coefficients.   • All other rules for the balanced equations are the same - omit spectator ions, assume a reaction occurs, write the formulas for molecular compounds (e.g. HF) as undissociated species in solution, etc.

  8. Synthesis or Combination Reactions • In synthesis or combination reactions, two or more substances combine together to form a single product. • The general form is A + B C • The products must contain only those elements found in the reactants.

  9. Metal + Nonmetal Salt • Magnesium ribbon is burned in oxygen • A strip of magnesium metal is heated strongly in pure nitrogen gas

  10. Synthesis • Solid calcium metal burns in air. • Balanced equation: • (ii) Predict the algebraic sign of entropy change for the reaction. Explain your prediction.

  11. Online Demos • Reaction of Magnesium and Oxygen • http://boyles.sdsmt.edu/magburn/magnesium_burning.htm • Reaction of Iron and Sulfur • http://www.pc.chemie.uni-siegen.de/pci/versuche/english/v21-1.html • Reaction of Potassium and Oxygen • http://neon.chem.ox.ac.uk/vrchemistry/FilmStudio/alkalimetals/HTML/page08.htm • Reaction of Lithium and Oxygen • http://neon.chem.ox.ac.uk/vrchemistry/FilmStudio/alkalimetals/HTML/page02.htm • Reaction of Lithium and Chlorine • http://neon.chem.ox.ac.uk/vrchemistry/FilmStudio/alkalimetals/HTML/page04.htm • Reaction of Sodium and Oxygen • http://neon.chem.ox.ac.uk/vrchemistry/FilmStudio/alkalimetals/HTML/page05.htm • Reaction of Zinc and Sulfur • http://boyles.sdsmt.edu/znsulf/zincsul.htm

  12. Nonmetal + Nonmetal Molecular compounds • Pure Solid Phosphorus (White Form) is burned in air • Reaction of Phosphorus and Chlorine • Website: http://boyles.sdsmt.edu/pwithcl/reaction_of_white_phosphorus_and.htm

  13. Hydrides • Preparation of the Group 1 hydrides • These are made by passing hydrogen gas over the heated metal. For example, for lithium hydride: • 2Li (s) + H2(g) 2LiH

  14. Nonmetal Oxide + Water Oxyacid • Oxy Acid= Contains H+ ions attached to common Polyatomic ion of Nonmetal Oxide plus one more oxygen • Solid dinitrogen pentoxide is added to water • Sulfur trioxide gas is bubbled into water

  15. Nonmetal Oxide + Water Oxyacid • Phosphorus (V) oxide powder is sprinkled over distilled water • Sulfur dioxide gas is bubbled into distilled water

  16. Nonmetal oxide + Oxygen • (c) Samples of nitrogen monoxide gas and oxygen gas are combined. • (ii) If the reaction is second order with respect to nitrogen monoxide and first order with respect to oxygen, what is the rate law for the reaction?

  17. Metal oxide + water metal hydroxide • Solid Cesium Oxide is added to water • Solid sodium oxide is added to distilled water • Powdered strontium oxide is added to distilled water • Calcium oxide powder is added to distilled water • Solid barium oxide is added to distilled water

  18. Metal Oxide and Water • Solid potassium oxide is added to water. • (i) Balanced equation: • (ii) If a few drops of phenolphthalein are added to the resulting solution, what would be observed? Explain.

  19. Demo

  20. Hydrogen-Nonmetal + Water Acidic Solution • Hydrogen Chloride gas bubbled into water

  21. Metal oxide + nonmetal oxide Yields metal ion attached to common polyatomic ion • Metal oxide + carbon dioxide metal carbonate • Carbon dioxide gas is passed over hot, solid sodium oxide • Metal oxide + sulfur dioxide Metal sulfite • Sulfur Dioxide is passed over solid calcium oxide

  22. DECOMPOSITION REACTIONS • Substances break down by means of decomposition reactions • The general form of a decomposition reaction is • C A + B • Decomposition reactions are the opposite of combination or synthesis reactions

  23. Decomposition of Metal Carbonate • Heating a metal carbonate always yields the metal oxide and carbon dioxide. • MCO3 MO + CO2 • Powdered magnesium carbonate is heated strongly • Solid calcium carbonate is strongly heated

  24. Metal Hydrogen Carbonate Decomposition • Heating a metal bicarbonate gives the metal oxide, carbon dioxide, and water. • MHCO3 MO + H2O + CO2 • http://www.chemguide.co.uk/inorganic/group1/compounds.html • Solid Sodium Hydrogen Carbonate is strongly heated

  25. Heating the nitrates • Most nitrates tend to decompose on heating to give the metal oxide, brown fumes of nitrogen dioxide, and oxygen. • For example, a typical Group 2 nitratelike magnesium nitrate decomposes like this: • In Group 1, lithium nitrate behaves in the same way - producing lithium oxide, nitrogen dioxide and oxygen. • The rest of the Groups, however, don't decompose so completely (at least not at Bunsen temperatures) - producing the metal nitrite and oxygen, but no nitrogen dioxide. 2 Mg(NO3)2 = 2 MgO + 2 NO2 + 3 O2

  26. Decomposition of Metal Hydroxides • Heating a metal hydroxide gives the metal oxide and water • MOH MO + H2O

  27. Metal Sulfite Decomposition • Heating a metal sulfite produces a metal oxide and sulfur dioxide • MSO3 MO + SO2 • Solid calcium sulfite is heated in a vacuum

  28. Metal Chlorate Decomposition • Heating a metal chlorate gives the metal chloride plus oxygen. • MClO3MCl + O2

  29. Decomposition • Solid potassium chlorate is strongly heated. •         Question: What is the oxidation number of chlorine before and after the reaction occurs?

  30. Electrolysis of Binary Compound • Electrolysis of a molten salt (ionic compound) separates the substance into its elements. • MN M + N

  31. Ammonium Compound Decomposition • Ammonium Carbonates • Solid ammonium carbonate is heated • Ammonium Hydroxide (NH4)2CO3 = 2NH3 + 2CO2 + H2O

  32. 2007 Questions (NH4)2CO3 = 2NH3 + 2CO2 + H2O

  33. Peroxide Decomposition • Elephant’s Toothpaste • Website: http://boyles.sdsmt.edu/tpaste/elephants.htm • Genie in a Bottle Demo • Website: http://boyles.sdsmt.edu/geniebot/genie.htm • Do not forget Group I Peroxides

  34. Reactions Based on Reduction Potentials EMF Potential • Reduction and Oxidation • Single replacement

  35. Cation Replacement • There are two types of single replacement reactions, in one, a metal or hydrogen replaces a positive ion • M0 + A+B- M+B- + A0

  36. Replacement of Hydrogen • Reaction of Magnesium and Different Concentrations of Acids • Website: http://boyles.sdsmt.edu/kinetic/mercadokinetics.htm • Hydrochloric Acid(g) + Magnesium(s)  Magnesium(II)Chloride(aq) + Hydrogen(g) • 2HCl(g) + Mg(s)  MgCl2(aq) + H2(g) • Small piece of sodium metal is added to distilled water • Website: http://boyles.sdsmt.edu/sodwat/reaction_of_sodium_and_water.htm • Sodium(s) + Water(l)  Sodium Hydroxide(aq) + Hydrogen(g) • 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)

  37. ) Reaction of Potassium and Water • Website: http://www.chem.shef.ac.uk/webelements-moov/K_H2O.mov • Potassium(s) + Water(l)  Potassium Hydroxide(aq) + Hydrogen(g) • 2K(s) + 2H2O  2KOH + H2(g) • A strip of zinc is added to a solution of 6.0-molar hydrobromic acid • Group I with water video • http://video.google.com/videoplay?docid=-2134266654801392897&q=rubidium+water

  38. 2007 Question

  39. Cation Replacement • Reaction of Zinc and Tin (II) Chloride • Website: http://www.chemtopics.com/lectures/unit02/lecture1/displace.htm • Zinc(s) + Tin (II) Chloride(aq)  Tin(s) + Zinc (II) Chloride(aq) • Zn(s) + SnCl2(aq) Sn(s) + ZnCl2(aq)

  40. Cation Replacement • 1. A strip of magnesium metal is added to an aqueous solution of silver nitrate. •         Question: Which substance is oxidized in the reaction?

  41. Cation Replacement • Zinc metal is placed into a solution of copper (II) sulfate. •         Question: Describe the change in color that the original solution undergoes as the reaction proceeds.

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