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  1. Chemical reactionstypes and balancing

  2. 2/14/11 – “C” day • Objective: To assess the concepts of ionic and covalent bonding. • Do Now: What property of water is determined by its shape? How do water molecules behave?

  3. 2/15/11 – “D” day • Objective: Introduce the concept of chemical reactions. • Do Now: Balance the following: • P4 + O2P4O6 Today: Check in HW Check Answers More Balancing Equations

  4. 2/16/11 – “E” day • Objective: To apply law of conservation of mass to chemical reactions. • Do Now: What is the law of conservation of mass? Today: Collect 11.1 Guided Read Chemical Reaction Notes Reaction in a Bag Lab

  5. Chemical reactions • When one or more reactants are changed into one or more products, a chemical reaction has occurred. • The atoms do not change, but are rearranged.

  6. Chemical reactions • The changing of substances into other substances by the breaking of old bonds and the formation of new bonds

  7. Terms to remember • The number in front of a substance is called the coefficient • The coefficient multiplies everything in the substance

  8. Terms to remember • Subscript – the number under an element – for example the 2 in O2 • The subscript tells how many of that type of atom is in a compound

  9. Practice • How many of each type of atom are there in 2 Al2(SO4)3? • 4 Al • 6S • 24 O

  10. Chemical reaction- example • Adding HCl to Zn • http://www.youtube.com/watch?v=HxiW2iPUZiw&feature=related How many safety mistakes can you find?

  11. Mistakes • Goggles? • Gloves? – Really strong HCl • Poor judgment – comment about holding balloon in teeth • Fire/explosion

  12. Zn + HCl • What happened? • How can you tell that a chemical reaction occurred?

  13. Chemical reaction • HCl + Zn → ZnCl2 + H2 The atoms in the products are the same atoms that were in the reactants, they are just arranged differently.

  14. Nomenclature • HCl + Zn → ZnCl2 + H2 Reactants → Products Reactants react to produce products

  15. LAW OF CONSERVATION OF MATTER • number and type  number and type • → READ as an = sign HCl + Zn → ZnCl2 + H2 Are there the same number of atoms of each type on each side of the →?

  16. Balancing equations • HCl + Zn → ZnCl2 + H2 • Step 1: Count the number of each type of atom on each side • H • Cl • Zn

  17. Balancing equations • HCl + Zn → ZnCl2 + H2 • Step 2: compare numbers, what needs to be changed to make them the same • H 1 → 2 • Cl 1 → 2 • Zn 1 → 1

  18. Balancing equations • 2HCl + Zn → ZnCl2 + H2 • Step 3: compare numbers, is it balanced now? • H 2 → 2 • Cl 2 → 2 • Zn 1 → 1

  19. Chemical Reaction 2 • H2 + O2 → H2O • Is this balanced? • How would you balance it?

  20. Chemical Reaction 2 • 2H2 + O2 → 2H2O

  21. Diatomic molecules • 7 elements, most of which we will use all the time, exist in nature as diatomic molecules, which means they only exist as a molecule of 2 atoms bonded together

  22. Diatomic molecules • H2, N2, O2, F2, Cl2, Br2 and I2 • Notice that all but H2 form a 7 on the periodic table. • You need to know these.

  23. Practice balancing equations Worksheets

  24. Types of reactions • Chemical reactions can be classified into 5 different types: • Synthesis • Decomposition • Single replacement • Double replacement • Combustion

  25. Synthesis reactions • Reactants: either 2 elements OR 2 compounds • Product: MUST be a compound USUALLY combination is 2 reactants 1 product A + B → AB

  26. Synthesis reactions • Examples N2 + 3H2 2NH3 2H2 + O2  2H2O

  27. Decomposition The opposite of synthesis One reactant making 2 or more products AB → A + B 2KClO3 2KCl + 3O2 2Ag2O  4Ag + O2

  28. Single Replacement • one atom takes the place of another atom in a compound A + BC  B + AC A has replaced B in this reaction

  29. Single Replacement • Examples • 2NaCl + F2 2NaF + Cl2 • Na + H2O  NaOH + H2 • K + MgBr2  KBr + Mg

  30. Double Replacement • When (usually) ions in 2 compounds switch places to form 2 new compounds. • AB + CD → AD + BC • Remember, positive charge (metal) is always written first

  31. Examples • CaCl2 + Na2SO4 → CaSO4 + 2 NaCl • FeCl2 + K2S  FeS + 2KCl

  32. Combustion • Reactants: Carbon and Hydrogen containing compound reacting with oxygen • Product: Carbon dioxide and water CxHy + O2CO2 + H2O

  33. Combustion • Examples • CH4 +3O2 → CO2 + 2 H2O • C3H8 + 5O2  3CO2 + 4H2O

  34. Types of reactions • Demonstration Lab

  35. Types of reactions • Types of chemical reactions IF WS

  36. Synthesis – Predicting products and balancing • Two or more reactants  one product Examples: Na + Cl2 2Na + Cl2 2NaCl

  37. Synthesis – Predicting products and balancing Rb + Cl2 Rb + Cl2 RbCl 2Rb + Cl2 2RbCl K + Cl2 K + Cl2  KCl not balanced 2K + Cl2  2KCl

  38. Decomposition • one reactant  two or more products • Exact opposite of a synthesis reaction

  39. Decomposition Seltzer water (carbonic acid) decomposes to produce carbon dioxide and water: H2CO3 CO2 + H2O Decomposition: one reactant, two (or more products)

  40. Decomposition

  41. Decomposition • Often decomposition requires adding energy. • If you add electricity to water, can make it decompose: H2O → H2 + O2 2H2O → 2H2 + O2

  42. Balancing Synthesis and Decomposition Reactions WS

  43. Single replacement reactions A + BC → B +AC • Two metals and one nonmetal OR AB + C →AC + B • Two nonmetals and one metal

  44. Single replacement

  45. Single Replacement Examples of two metals and one nonmetal Al + CuCl2 AlCl3 + Cu Balance: 2Al + 3CuCl2 2AlCl3 + 3Cu

  46. Single Replacement Examples of two nonmetals and one metal Mg + HCl  MgCl2 + H2 • Balance • Mg + 2HCl  MgCl2 + H2

  47. Try these SR reactions Use the following steps: • Identify which reactants are switching places • Determine neutral ratio for new compound • Draw reaction arrow and complete reaction • MgBr2 and Cl2 • KI and F2

  48. Answers 1. Magnesium Bromide and Chlorine • MgBr2 + Cl2 . • Bromine and Chlorine • ==> MgCl2 + Br2 2. Potassium Iodide and Fluorine • 2KI + F2 • Iodine and Fluorine • ==> 2KF + I2

  49. Balancing SR reactions WS