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What is the difference between a chemical reaction and physical change?

What is the difference between a chemical reaction and physical change? When you watch a reaction occur, what are some hints that it is a chemical reaction?. Ch. 11 Chemical Equations Reactions. Describing Chemical Reactions. Objectives.

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What is the difference between a chemical reaction and physical change?

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  1. What is the difference between a chemical reaction and physical change? • When you watch a reaction occur, what are some hints that it is a chemical reaction?

  2. Ch. 11 Chemical Equations Reactions Describing Chemical Reactions

  3. Objectives • List three observations that suggest that a chemical reaction has taken place. • List three requirements for a correctly written chemical equation. • Write a word equation and a formula equation for a given reaction. • Balance a formula equation by inspection.

  4. Chemical Reactions • when a substance changes identity • reactants- original • products- resulting • law of conservation of mass • total mass of reactants = total mass of products

  5. Chemical Reactions • chemical equation • represents identities and relative amounts of reactants and products in the chemical reaction • uses symbols and formulas

  6. Hints of Chemical Rxn • heat or light • can also happen with physical changes • gas bubbles • means a gas is being created as product • precipitate • solid is being created • color change

  7. Writing Chemical Equations • most pure elements • written as elemental symbol • diatomic molecules • molecule containing only 2 atoms • some elements normally exist this way • H2, O2, N2, F2, Cl2, Br2, I2 • other exceptions • sulfur: S8 • phosphorus: P4

  8. Word Equations • uses names instead of formulas • helps you to write formula equation

  9. Example • Description: Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. • Word Equation: sodium oxide + water  sodium hydroxide • Formula Equation: Na2O + H2O  NaOH

  10. yields reversible above arrow: or heat heated MnO2 or Pt catalyst 25°C specific T requirement 2 atm specific P requirement after a formula: (s) solid (l) liquid (aq) aqueous: dissolved in water (g) gas Symbols Used in Equations

  11. Text Pg. 323 Chart of symbols used in chemical equations

  12. List three observations that suggest that a chemical reaction has taken place.

  13. Acids you have to know! • HCl hydrochloric acid • H2SO4 sulfuric acid • HNO3 nitric acid • H3PO4 phosphoric acid • HC2H3O2 acetic acid

  14. Write the chemical equation from the following description: Zinc metal is added to hydrochloric acid to create zinc chloride and hydrogen gas.

  15. Aluminum reacts with oxygen to produce aluminum oxide • Al + O  Al2O3 • Al + O2 Al2O3 • Al3 + O  Al2O3

  16. Aluminum reacts with oxygen to produce aluminum oxide • Al + O  Al2O3 • Al + O2 Al2O3 • Al3 + O  Al2O3

  17. Phosphoric acid is produced through the reaction between tetraphosphorus decoxide and water • H3PO4 P4 + H2O • H3PO4 + H2O  P4 • P4O10 + H2O  H3PO4

  18. Phosphoric acid is produced through the reaction between tetraphosphorus decoxide and water • H3PO4 P4 + H2O • H3PO4 + H2O  P4 • P4O10 + H2O  H3PO4

  19. Iron(III)oxide reacts with carbon monoxide to produce iron and carbon dioxide • FeO + CO Fe + CO2 • Fe2O3 + CO  Fe + CO2 • Fe + CO Fe2O3 + CO2

  20. Iron(III)oxide reacts with carbon monoxide to produce iron and carbon dioxide • FeO + CO Fe + CO2 • Fe2O3 + CO  Fe + CO2 • Fe + CO Fe2O3 + CO2

  21. Coefficients • whole numbers in front of formula • distributes to numbers of atoms in formula • specifies the relative number of moles and molecules involved in the reaction • used to balance the equation

  22. Balancing Equations • ONLY add/change coefficients- NEVER subscripts!!! • balance one type of atom at a time • balance polyatomic ions first • balance atoms that appear only once second • balance H and O last • simplify if you can • Check at end!

  23. Rules for writing and balancing equations – Pg. 327 in text.

  24. Writing Equations • Write Word equations to help you organize reactants and products • Be sure to include symbols showing states of each reactant and product • Be sure to write the correct formula for each (crossing over for ionic compounds!) • Check your balancing of the equation when you are finished

  25. Example 1 • Description: • Aqueous iron III oxide reacts with hydrogen gas to produce iron metal and liquid water Word Equation: Iron III oxide + hydrogen gas  iron + water

  26. Example 1 • Formula Equation: Fe2O3 (aq) + H2(g) Fe (s) + H2O (l) • Balanced Formula Equation Fe2O3(aq) + 3H2(g) 2Fe (s) + 3H2O (l)

  27. Example 2 • Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. • calcium + water  calcium hydroxide + hydrogen • Ca(s) + H2O(l) Ca(OH)2(aq) + H2(g) • Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g)

  28. Example 3 • solid zinc metal reacts with aqueous copper (II) sulfate to produce solid copper metal and aqueous zinc sulfate • zinc + copper (II) sulfate  copper + zinc sulfate • Zn(s) + CuSO4 (aq)  Cu (s) + ZnSO4 (aq) • Zn(s) + CuSO4 (aq)  Cu(s) + ZnSO4 (aq)

  29. Example 4 • Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water • hydrogen peroxide  oxygen + water • H2O2 (aq)  O2 (g) + H2O (l) • 2H2O2 (aq)  O2 (g) + 2H2O (l)

  30. Example 5 • Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper (II) nitrate • copper + silver nitrate  silver + copper (II) nitrate • Cu (s) + AgNO3 (aq)  Ag (s) + Cu(NO3)2 (aq) • Cu (s) + 2AgNO3 (aq)  2Ag (s) + Cu(NO3)2 (aq)

  31. Example 6 • Carbon dioxide gas is bubbled through water containing solid barium carbonate, creating aqueous barium bicarbonate • carbon dioxide + water + barium carbonate  barium bicarbonate • CO2 (g) + H2O (l) + BaCO3 (s) Ba(HCO3)2 (aq) • CO2 (g) + H2O (l) + BaCO3 (s) Ba(HCO3)2 (aq)

  32. Example 7 • Acetic acid solution is added to a solution of magnesium bicarbonate to create water, carbon dioxide gas, and aqueous magnesium acetate. • acetic acid + magnesium bicarbonate  water + carbon dioxide + magnesium acetate • HCH3COO (aq) + Mg(HCO3)2 (aq)  H2O(l) + CO2 (g) + Mg(CH3COO)2 (aq) • 2HCH3COO (aq) + Mg(HCO3)2 (aq)  2H2O(l) + 2CO2 (g) + Mg(CH3COO)2 (aq)

  33. Write the balanced formula equation for: Lithium metal is added to a solution of aluminum sulfate to make aqueous lithium sulfate and aluminum metal.

  34. Types of Chemical Reactions

  35. Types of Chemical Reactions • 5 basic types discussed here • not all reactions fall in these categories • you should be able to: • categorize a reaction • predict the product(s)

  36. 1. Synthesis • also called combination reaction • reactants: • more than one • can be elements or compounds • products: only one compound A + X  AX where A is the cation and X is anion

  37. 1. Synthesis • Rubidium and sulfur Rb(s) + S8 (s) Rb2S (s) • Magnesium and oxygen Mg (s) + O2 (g) MgO(s) • Sodium and chlorine Na (s) + Cl2 (g) NaCl(s) • Magnesium and fluorine Mg (s) + F2 (g) MgF2 (s)

  38. 1. Synthesis • calcium oxide and water CaO(s) + H2O(l) Ca(OH)2 (aq) • sulfur dioxide and water SO2 (g) + H2O (l) H2SO3 (aq) • calcium oxide and sulfur dioxide CaO(s) + SO2 (g) CaSO3 (s)

  39. 2. Decomposition • opposite of synthesis • usually require energy • reactants: only one compound • products: more than one • usually elements but can be compounds AX  A + X

  40. 2. Decomposition • water H2O (l) H2 (g) + O2 (g) • calcium carbonate CaCO3 (s) CaO(s) + CO2 (g) • calcium hydroxide Ca(OH)2 (s) CaO(s) + H2O (l) • carbonic acid H2CO3 (aq)  CO2 (g) + H2O (l)

  41. 3. Single Replacement • an element replaces a similar element in a compound • reactants: 1 element & 1 compound • products: 1 element & 1 compound A + BX  B + AX Y + AX  X + AY

  42. 3. Single Replacement • zinc and hydrochloric acid Zn (s) + HCl(aq)  ZnCl2 (aq) + H2 (g) • iron and water Fe (s) + H2O (l)  FeO(aq) + H2 (g) • magnesium and lead (II) nitrate Mg (s) + Pb(NO3)2 (aq)  Mg(NO3)3 (aq) + Pb(s) • chlorine and potassium bromide Cl2 (g) + KBr(s)  KCl(s) + Br2 (g)

  43. 4. Double Replacement • two similar elements switch places • reactants: 2 compounds • products: 2 compounds AX + BY  BX + AY

  44. 4. Double Replacement • barium chloride and sodium sulfate BaCl2 (aq) + Na2SO4 (aq)  NaCl(aq) + BaSO4 (s) • iron sulfide and hydrochloric acid FeS(aq) + HCl(aq)  FeCl2 (aq) + H2S (g) • hydrochloric acid and sodium hydroxide HCl(aq) + NaOH (aq)  NaCl(aq) + H2O (l) • potassium iodide and lead (II) nitrate KI (aq) + Pb(NO3)2 (aq)  KNO3 (aq) + PbI2 (s)

  45. 5. Combustion • Only responsible for one type • releases energy in form of heat/light • reactants: hydrocarbon + O2 • H2O and CO2 as the only products Ex: CH4 + O2 CO2 + H2O

  46. Combustion • propane and oxygen C3H8(g) + O2(g)  CO2(g) + H2O(g)

  47. Practice Classify each of the following reactions one of the five basic types: • Na2O + H2O  NaOH • synthesis • Zn (s) + 2HCl (aq)  ZnCl2 (aq) + H2 (g) • single replacement • Ca(s) + 2H2O (l) Ca(OH)2 (aq) + H2 (g) • single replacement

  48. Practice • 2H2O2 (aq)  O2 (g) + 2H2O (l) • decomposition • Cu (s) + 2AgNO3 (aq)  2Ag (s) +Cu(NO3)2 (aq) • single replacement • C2H4 (g) + O2 (g)  CO2 (g) + H2O (g) • combustion • ZnO(s) + C (s)  2Zn (s) + CO2 (g) • single replacement

  49. Practice • Na2O (s) + 2CO2 (g) + H2O (l) NaHCO3 (s) • synthesis • Ca(s) + H2O(l)  Ca(OH)2(aq) + H2 (g) • single replacement • KClO3 (s)  KCl(s) + O2 (g) • decomposition • H2SO4 (aq) + BaCl2 (aq)  HCl(aq) + BaSO4 (s) • double replacement

  50. Activity Series

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