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Unit 6 Chemical Reactions

Unit 6 Chemical Reactions. General Chemistry Spring 2010. Section 1. NOMENCLATURE REVIEW. Ionic. Basic Rules These have a cation (+) and an anion (-) Usually a metal and a nonmetal Sometimes contain polyatomic ion(s) (back of PT) Pay attention to charges

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Unit 6 Chemical Reactions

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  1. Unit 6Chemical Reactions General Chemistry Spring 2010

  2. Section 1 NOMENCLATURE REVIEW

  3. Ionic • Basic Rules • These have a cation (+) and an anion (-) • Usually a metal and a nonmetal • Sometimes contain polyatomic ion(s) • (back of PT) • Pay attention to charges • Overall charge on ENTIRE formula has to be ZERO • Use subscripts to add charge to make zero • Criss-cross is a shortcut but be careful! • Practice this on the next slide

  4. Basic Ionic Formula • Give the formulas for the following compounds w/o PAI • Potassium sulfide • Magnesium oxide • Give the formulas w/ PAI • (DON’T CHANGE THE FORMULA) • Aluminum nitrate • Calcium phosphate

  5. Transition Metals • In the name, charge on TM is in () • Ex) Iron (III) chloride • Ex) Tin (II) fluoride • Use that charge to do criss-cross • To figure out the TM charge do reverse criss-cross. The charge is on ONE TM! • Ex) CuO • Ex) Cu2O

  6. Covalent Nomenclature • NO CRISS CROSS!!! NO REDUCE!!! • The subscript after the symbol = the prefix in the name • The prefix in the name = the subscript in the formula (what are these rules?) • Ex) NO2 • Ex) N2O • Ex) Sulfur hexafluoride • Ex) Triphosphorus pentachloride Diatomic molecules

  7. Acids • Every acid formula begins with hydrogen • The other half is either a halogen or a polyatomic ion • Halogen? Use “hydro” in name • Ex) HCl • Ex) HF • Polyatomic? Change ending to “-ic” (for this class) • Ex) H3PO4 • Ex) H2SO4 • # of H’s is the charge on the PAI

  8. Section 2 Counting Atoms Review

  9. Subscript • Indicates the number present • Only applies to the element it’s with • AlCl3 • One aluminum and three chlorines

  10. Subscripts • When an element has no subscript • The implied subscript is ONE • Ag1 = Ag

  11. Coefficient • Affects anything behind it • Multiply everything by the coefficient • 3 AlCl3 • Three aluminums and nine chlorines

  12. Section 3 Reaction Basics

  13. Chemical Equations • The “sentences” of chemistry • Show how elements react with each other and what compounds they will form So that’s what happens when sodium and water mix!!!!

  14. Parts of a chemical Equation • Reactants • Always on the left of the equation • What the reaction STARTS with • Products • Always on the right of the equation • What is produced from the reaction (made) • Yield • Arrow • Where the reaction actually occurs

  15. Can you show me what you just said??? Yield Sign Mg + O2 MgO Reactants Products

  16. Symbols in Equations (Table 11.1)

  17. Section 4 Inventory Reactions

  18. Law of Conservation of Mass • The reason we balance reactions • Matter is neither created nor destroyed • Must account for all elements • Before and after reaction Antoine-Laurent de Lavoisier was the first to state this law.

  19. Reaction Anatomy Reactant(s) Products KClO3 KCl + O2 K 1 Cl 1 O 3 K 1 Cl 1 O 2

  20. Inventory • Compare the number of each atom in the reactants to the products • If equal = “balanced reaction” • Abides by the law of conservation of mass • If not equal = “not balanced” • Does not abide by the law of conservation of mass; MUST BALANCE Reactant(s) Products KClO3 KCl + O2 K 1 Cl 1 O 3 K 1 Cl 1 O 2 “Not balanced”

  21. Section 5 Balancing Reactions

  22. KClO3 KCl + O2 K 1 Cl 1 O 3 K 1 Cl 1 O 2 Balance It’s best to leave H and O for the end • Inventory first • Locate one element that does not balance • Add a coefficient to make it balance • NEVER TOUCH A SUBSCRIPT • Look to make odd numbers even • Re inventory • Repeat until balanced 2 2 3 balanced 2 2 2 2 6 6

  23. Balancing • When balancing a chemical equation you may only change the coefficient (big number in front of the substance) • Balancing example #1: • Mg(s) + O2(g) MgO(s) 2 2 / 2 / 2 2 / • Mg 1 • 2 O 1

  24. Balance Combustion = 2 CHOR • Combustion is any reaction with CO2 + H2O for products • 2…coefficient of 2 in front of big hydrocarbon • C…balance carbons • H…balance hydrogen • O…balance oxygen • R…reduce if possible (divide by a common factor, like 2) H C 1 11 7 8 2 C7H16 + O2 CO2 + H2O 22 14 16

  25. Balancing (cont.) • When balancing a chemical equation you may only change the coefficient (big number in front of the substance) • Balancing example #3: • NaOH(aq) + H2SO4(aq)  Na2SO4(aq) + HOH(l) 2 2 2 / 2 / • Na 2 • 1 OH 1 • 2 H 1 • 1 SO4 1 Count polyatomic ions as one piece! / 2 / 2

  26. 5 2 2 2 Practice Problem #1 • Balance the following reactions: • P4(s) + O2(aq) P4O10 • Zn + HCl  ZnCl2 + H2(g) • Mg(s) + O2(g) MgO(s) • KClO3 KCl + O2(g) 2 2 3

  27. Section 6 Reaction Types

  28. Sorting into piles makes it easier to see the similarities and differences Reaction Types • Chemical reactions are classified into 5 different types: • This makes it easier to see what is happening in a reaction • This makes it easier to predict products in a reaction

  29. Reaction Types (cont.) • Five reaction types • 1) Synthesis (Combination) • 2) Decomposition • 3) Single Replacement • 4) Double Replacement • 5) Combustion Now let’s look at each type individually

  30. Please Note • The following reactions are not balanced • The examples are only used to show the type of reaction

  31. Synthesis = S (Note: The book uses the term “combination;” it’s the same thing) • Two or more substances react to form one new compound • Element + element  new compound • compound + compound  new compound • Examples • H2 + N2 NH3 • Mg + O2 MgO (magnesium oxide)

  32. Decomposition = D • One compound breaks into two or more simpler products • Compound  element/compound + element/compound • Examples • Na2O  Na + O2 • NH4NO3  N2O + H2O • Ammonium nitrate, when heated, explosively breaks down!

  33. Single Replacement = SR • Element + compound  new element + new compound • Examples • AlCl3 + O2  Al2O3 + Cl2 • H2(SO4) + K  K2(SO4) + H2 • Br2 + NaI  NaBr + I2 • Br2 + NaCl  No Reaction • Halogen activity decreases as you go down group

  34. Activity Series • Whether one metal displaces another depends on upon the reactivities of the metals • A reactive metal will replace any metal listed below it on the activity series • Ex) iron will displace copper from a copper compound, but iron does not similarly displace zinc or calcium

  35. Double Replacement = DR • Compound + compound  new compound + new compound • Examples • Na2O + MgBr2 NaBr + MgO • H(NO3) + Mg(OH)2  H(OH) + Mg(NO3)2 Which switch? Think about Paula Abdul when you rewrite the formulas!

  36. Combustion = C • An element or a compound reacts with oxygen, usually producing heat and light • Always involves oxygen as a reactant • Reaction with CO2 + H2O for products • Examples • C6H12O6 + O2 CO2 + H2O • 2 C8H18 + 25 O2 16 CO2 + 18 H2O

  37. Double Replacement Single Replacement Combustion Decomposition Synthesis Visual Review of Types of Reactions

  38. Section 7 Predicting Products(p.338-339)

  39. Synthesis (cont.) • Steps to predict products: • 1. Combine the two reactants in one product (switchy switchy • 2. Balance Steps in the Irish Countryside

  40. 2 2 2 4 Practice Problem #4 • Predict the product and balance: • Mg(s) + O2(g) • Be(s) + Br2(g)  • Cs(s) + S2(g)  MgO(s) BeBr2(s) Cs2S(s)

  41. Decomposition (cont.) • Steps to predict products: • 1. Break the one reactant into two products • Don’t forget about diatomic moleculesH, N, O, F, Cl, Br, I • 2. Balance Ancient Steps in Cancun, Mexico

  42. 2 2 Practice Problem #5 • Predict the products and balance: • MgCl2(s) • FeS(s)  • NaI(s)  Mg(s) + Cl2(g) Fe(s) + S(s) Na(s) + I2(s)

  43. Single Replacement (cont.) • Steps to predict products: • 1. Figure out which metal is going to replace which other metal • 2. Write the products: • One metal is now by itself • One metal is now part of a compound (Switchy Switchy) • 3. Balance Steps to the House of the Ñusta at Machu Picchu

  44. 3 2 2 3 Practice Problem #2 • Predict the products and balance: • K(s) + MgS(aq) • Ba(s) + Au(C2H3O2)3(aq)  • Zn(s) + HCl(aq)  2 Mg(s) + K2S(aq) Au(s) + Ba(C2H3O2)2(aq) 2 H2(s) + ZnCl2(aq)

  45. Double Replacement (cont.) • Steps to predict products: • 1. Figure out which metal is going to trade partners with which other metal • 2. Write the products: • One metal is now in a compound with the other anion (switchy switchy) • One metal is now in a compound with the other anion (switchy switchy) • 3. Balance Steps on a Sand Dune at the edge of the Gobi Desert

  46. Practice Problem #3 • Predict the products and balance: • FeS(s) + HCl(aq) • CaCl2(aq) + H2SO4(aq)  • NH4I(aq) + AgNO3(aq)  2 FeCl2(aq) + H2S(g) 2 HCl(aq) + CaSO4(s) NH4NO3(aq) + AgI(s)

  47. Combustion (cont.) • Steps to predict products: • 1. Write CO2 and H2O as the products • 2. Balance…2CHOR • 1st balance C • 2nd balance H • 3rd balance O Steps to the Lincoln Memorial

  48. 5 3 4 2 15 10 12 2 8 13 10 Practice Problem #6 • Predict the products and balance: • C3H8(g) + O2(g) • C5H12O(s) + O2(g) • C4H10(s) + O2(g) CO2(g) + H2O(l) CO2(g) + H2O(l) CO2(g) + H2O(l)

  49. Section 8 Reaction Rates and Equilibrium

  50. Energy Basics • For a reaction to proceed… • Reactants’ bonds must break • Bonds must reform to make products • Energy is required to break reactants apart (their bonds) • Reactions either gain or lose energy, they never stay the same

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