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Chemical Reactions

Chemical Reactions. Chemical Reactions are all around us. Describing Chemical Reactions. c hemical change - rearrangement of atoms to form a new substance. Has new chemical and physical properties. Evidences of a Chemical Reaction. Produce a gas Produce a solid (precipitate)

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Chemical Reactions

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  1. Chemical Reactions

  2. Chemical Reactions are all around us

  3. Describing Chemical Reactions • chemical change - rearrangement of atoms to form a new substance Has new chemical and physical properties

  4. Evidences of a Chemical Reaction • Produce a gas • Produce a solid (precipitate) • Color change • Odor change • Temperature change • Exothermic • Endothermic • Give off heat/light • Produce sound

  5. Chemical Reaction vs. Physical Change • To prove a chemical change took place, you have to do a chemical analysis • Properties of a new substance must differ from the original substance

  6. Analogy! • Physical change is like printing a word in a different font, it’s the same word just looks different! stampedes stampedes • Chemical change is like scrambling letters to form new words made + steps  stampedes

  7. Remember… • All changes of state: Solid Liquid  Gas • Evaporation • Condensation • Melting • Freezing Are Physical Changes!

  8. Physical or Chemical Change?

  9. Physical or Chemical Change?

  10. Physical or Chemical Change?

  11. Physical or Chemical Change?

  12. Physical or Chemical Change?

  13. Physical or Chemical Change?

  14. Physical or Chemical Change?

  15. Physical or Chemical Change? Rotten Egg

  16. Physical or Chemical Change?

  17. Physical or Chemical Change?

  18. Physical or Chemical Change?

  19. Physical or Chemical Change?

  20. Physical or Chemical Change?

  21. What causes Chemical Reactions?

  22. Reaction and Energy Changes • Chemical Reactions either RELEASE or ABSORB energy.

  23. Release Energy Example: • Natural Gas • Methane + Oxygen  Carbon Dioxide + Water + ENERGY

  24. Absorb Energy Example: • Photosynthesis • Carbon Dioxide + Water + ENERGY  Oxygen + Glucose

  25. Chemical Equations • Equations are used to represent chemical reactions • Reactants – starting substances • Products – new substances Reactants Product

  26. Chemical Equations • Arrow always points to the product Hydrogen + Oxygen Water Mercury Oxide Liquid Mercury + Oxygen Sodium Chloride Sodium + Chlorine

  27. Word Equations – uses names • Names of the reactants separated by a + • Arrow separates reactants from products • Names of products separated by a + Example: Hydrogen + Oxygen Water

  28. Formula Equations – uses symbols • Symbol of the reactants separated by a + • Arrow separates reactants from products • Symbol of the products separated by a + Example: H₂ + O₂ H₂O

  29. Writing word and formula equations: • Mercury oxide is heated to form liquid mercury and oxygen • Word = • Formula =

  30. Common symbols in equations • → : produces or forms • + : plus • (s) : solid • (l) : liquid • (g) : gas • (aq) : aqueous - dissolved in water

  31. Add the symbols Hydrogen + Oxygen Water Mercury Oxide Mercury + Oxygen Sodium Chloride Sodium + Chlorine

  32. Common symbols in equations • Reversible • 1803 a scientist observed the formation of sodium carbonate crystals at the edge of a salt lake 2NaCl + CaCO3 → Na2CO3 + CaCl2. He recognized this as the reverse of the familiar reaction Na2CO3 + CaCl2→ 2NaCl + CaCO3. He reasoned that the excess of salt in the lake helped push the "reverse" reaction towards the formation of sodium carbonate

  33. Common symbols in equations KI • ______ The element symbol above the arrow indicates a catalyst. • A catalyst is something that speeds up the reaction but is not changed during the reaction, so it goes above the arrow.

  34. Review writing ionic compounds Magnesium Nitride Iron (III) Oxide Sodium Sulfide Copper (II) Chloride

  35. Seven diatomic elements: • Hydrogen (H2) • Nitrogen (N2) • Oxygen (O2) • Fluorine (F2) • Chlorine (Cl2) • Iodine (I2) • Bromine (Br2) Write these on back of periodic table!

  36. Common Polyatomic Ions • Write these down on the backs of your periodic tables

  37. Writing polyatomic compounds • Aluminum Hydroxide • Mercury (II) Phosphate • Aluminum Sulfate • Copper (II) Bromide • Lead (II) Chlorite • Silver Cyanide • Ammonium Oxide

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