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Unit 6

Unit 6. Chemical Reactions: An Introduction. Evidence of a Chemical Reaction. Color change Temperature change Formation of a gas (bubbles) Formation of a precipitate (a solid forming when 2 solutions are mixed together). Principles of Chemical Reactions:.

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Unit 6

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  1. Unit 6 Chemical Reactions: An Introduction

  2. Evidence of a Chemical Reaction • Color change • Temperature change • Formation of a gas (bubbles) • Formation of a precipitate (a solid forming when 2 solutions are mixed together)

  3. Principles of Chemical Reactions: • A chemical equation tells you what reactant chemicals are used and what product chemicals are formed. • A chemical equation does not tell you how long the chemical reaction will take, how to mix the chemicals, or at what temperature.

  4. 2 H2 + 1 O22 H2O • The numbers in front of the chemicals, the coefficient, tell you the number of atoms and molecules involved, or the number of moles involved. 2 molecules of hydrogen are added to 1 molecule of oxygen makes (yields) 2 molecules of water. 2 moles of hydrogen are added to 1 mole of oxygen makes (yields) 2 moles of water.

  5. Law of Conservation of Mass • You can not destroy or create substances in a chemical reaction. You simply change how they appear. • Mass at beginning = Mass at end of of reaction reaction

  6. To balance equations: • a. Know what the reactants and products are • A + B  C + D • reactants products • Know the correct formula for each substance • c. Conserve atoms by placing coefficients in front of the chemicals so that you have the same number of atoms of each element on opposite sides of } }

  7. Notation of phase may be used. s = solid L = liquid g = gas aq = aqueous (dissolved in water) Zn(s) + 2 HCl(aq) ZnCl2 (aq) + H2 (g)

  8. Balancing equations using molecule model kits: H2 + O2  H2O

  9. Element colors Hydrogen – Yellow Carbon – Black Nitrogen – Blue Oxygen – Red Chlorine - Green

  10. Types of Chemical Reactions Synthesis X + Y  XY Decomposition XY  X + Y Combustion CxHyYz + O2 CO2 + H2O Single Replacement A + XY  AY + X Double Replacement AB + XY  AY + XB

  11. Types of chemical reactions: • Synthesis (or combination): combining 2 or more small molecules or atoms into one larger molecule Synthesis X + Y  XY H2(g) + O2(g) H2O (g)

  12. Decomposition: breaking a large molecule into 2 or more smaller molecules or atoms Decomposition XY  X + Y (NH4)2Cr2O7(s)  N2(g) + H2O (g) + Cr2O3(s) Combustion: a hydrocarbon molecule combining with oxygen to make CO2 and H2O Combustion CxHyYz + O2 CO2 + H2O C2H6O (g) + O2(g) CO2(g) + H2O (g)

  13. Single replacement: an element exchanges places with another element in a compound to make a new element and a new compound Single Replacement A + XY  AY + X AgNO3(aq) + Cu (s) Cu(NO3)2(aq) + Ag (s) Double replacement: when 2 compounds exchange partners to make 2 new compounds Double Replacement AB + XY  AY + XB FeCl3(aq) + NaOH (aq) Fe(OH)3(s) + NaCl (aq)

  14. Writing balanced ionic equations for chemicals dissolving in H2O NaCl (s) NH4Cl (s)  CaCl2 (s)  (NH4)2CO3 (s) 

  15. AgNO3 (s) CuCl2 (s)  NaHCO3 (s)  Na2SO4 (s) 

  16. Types of Chemical Reactions Synthesis X + Y  XY Decomposition XY  X + Y Combustion CxHyYz + O2 CO2 + H2O Single Replacement A + XY  AY + X Double Replacement AB + XY  AY + XB

  17. .50 mol 1.00 mol Fe2O3 + C  Fe + CO 2 ____g 12.01g ____g ____g

  18. Some reactions give off energy. These are called exothermic chemical reactions. CaO (s) + H2O (L)  Ca(OH)2(s) Some reactions absorb energy. These are called endothermic chemical reactions. Ba(OH)2.8H2O(s) + NH4NO3(s) Ba(NO3)2(aq) + NH3(g) +H2O(L) Some chemical reactions are reversible. 2 H2(g) + O2(g) 2 H2O (g) + energy energy + 2 H2O (L)  2 H2(g) + O2 (g)

  19. Review 1. 2C3H8O + 9O2 6CO2 + 8H2O 2H2O2 2H2O + O2 3C + 2Fe2O3 3CO2 + 4 Fe 6CO2 + 6H2O  C6H12O6 + 6 O2 2NaCl + Pb(NO3)2 PbCl2 + 2 NaNO3 2 H2 + O2 2 H2O 2. Synthesis – f, decoposition – b, single replacement – c, double replacement – e, combustion – a (d doesn’t fit any of these) 3. 4Fe + 3 O2 2 Fe2O3 4. Ba(NO3)2 Ba+2 + 2 NO3-1 AlCl3 Al+3 + 3 Cl-1 (NH4)3PO4 3NH4+1 + PO4-3 5. .20 mol .40 mol CaCO3 + 2HCl  CaCl2 + H2CO3 20.02g 14.58g 22.20g 12.40g

  20. Use on the exam: • Periodic Table • Formula sheet • Mole Wheel • Common Ions • Calculator • Blank Periodic Table (you wrote on)

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