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Chemical Reactions

Chemical Reactions. Def’n: A reaction is a bond rearrangement that results in new substances The new substance = products The substances that react = reactants. Chemical reactions are written as: reactants  products “” means “produces” Example:

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Chemical Reactions

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  1. Chemical Reactions • Def’n: A reaction is a bond rearrangement that results in new substances • The new substance = products • The substances that react = reactants

  2. Chemical reactions are written as: reactants products “” means “produces” Example: HCl(aq) + NaHCO3(s) NaCl(aq) +H2O(l) + CO2(g)

  3. Combustion: hydrocarbon compounds combine with O2 to produce CO2 and H2O

  4. Acid / Base neutralization

  5. Formation of a precipitate: a solid substance is produced Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

  6. Corrosion: rust, oxidation, metal combines with O2 to produce a “metal oxide” Fe(s) + O2(g) FeO2(s)

  7. Electrolysis: electric current forces a decomposition reaction; breaks a compound into its individual elements 2H20(l) + energy  2H2(g) +O2(g)

  8. Evidence of Reaction • Color change • Odour change • Precipitate is formed • Gas produced (bubbles, odor) • Energy change (heat, light, sound)

  9. Energy Changes • Energy released = exothermic. The energy exits from the compound. eg. combustion, use a battery, sound • Energy absorbed = endothermic. The compound takes in energy from the environment. eg. photosynthesis, recharge a battery, cold packs

  10. Solubility • Solubility measures how much “solute” dissolves in a “solvent” (usually water). miscible  soluble  low solubility  insoluble alcohol salt chalk wax

  11. Determined by experience (sugar) or a “solubility table”. • Often (s) indicates low solubility or (aq) indicates dissolves well in water.

  12. For an ionic compound to be soluble in water the affinity an ion has for the polar water molecules has to be higher than the attraction to the oppositely charged ions.

  13. Table 3.2 Solubility of Ionic Compounds in Water at 25°C

  14. Self Check • Predict the solubility of the following: • AgCl • Ba(OH)2 • FeS • Na3PO4 • CuBr and CuBr2

  15. Precipitates • Precipitates are low soluble ionic products of a chemical reaction. • Which substances in the previous slide could be “precipitates”?

  16. Conservation of Energy • Energy comes in many forms (Ep and Ek) • If all forms are carefully measured, • Energy is conserved during all reactions • Energy is required to break bonds, and is released when bonds form.

  17. Law of Conservation of Energy • Energy can be converted from one form to another, but the total energy of the universe remains constant.

  18. Practice: Page 90 #1-4 Page 93: All

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