Predicting Reactions

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

15. 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

16. 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

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

19. 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?

20. 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

21. 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.

22. Demo

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

25. 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

26. 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

27. 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

28. 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

29. 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

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

31. 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

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

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

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

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

36. 2007 Questions (NH4)2CO3 = 2NH3 + 2CO2 + H2O

38. 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

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

41. 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

44. 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)

45. ) 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

46. 2007 Question

48. 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)

49. 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?

50. 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.