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Chemical Change

Chemical Change. Chapter 3 Section 3.1. Objectives. Identify important reactions in society Recognize and identify evidence for chemical changes Differentiate between endothermic and exothermic reactions Describe the Law of Conservation of Mass. To Start.

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Chemical Change

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  1. Chemical Change Chapter 3 Section 3.1

  2. Objectives • Identify important reactions in society • Recognize and identify evidence for chemical changes • Differentiate between endothermic and exothermic reactions • Describe the Law of Conservation of Mass

  3. To Start • What is the difference between a chemical and physical change? • Chemical change- something new is created with its own unique properties • Physical change- nothing new is created (just changing states) • What are the three states?

  4. Chemical or Physical? • Which of the following are chemical changes? Physical changes?

  5. Chemical Change • Reactant + reactant  product(s) • Products have different properties than reactants • Properties include: state at RT, temperature, melting point, color and density • Includes a flow of energy • IMPORTANT: drives chemical reactions • Can be fast or slow

  6. Examples of Chemical Reactions • Batteries • Combustion Engine • Wine production • Baking bread • Photosynthesis • Cellular respiration (making energy in our bodies)

  7. Evidence of a Chemical Change • What are ways that we know a chemical change has occurred? • Formation of a gas (bubbles) • Air bag inflation in a car • Color change • Sugar and sulfuric acid • Formation of a precipitate (change in state) • Mixing silver nitrate with sodium chloride • Flow of energy (usually detected as a change in temperature) • Combustion (lighting a match)

  8. Formation of a Gas: Demo • What will happen when I add baking soda to vinegar in this beaker? • What will happen to the balloon placed over the top? • What gas is produced? • What other examples do we have of a formation of a gas?

  9. Energy Changes • Two types of energy changes: • Exothermic- release of energy (*exit) • Endothermic- absorption of energy (*enter) • What change of temperature would you feel with each of these processes? • Can physical changes be exothermic and endothermic? Why or why not?

  10. Exothermic Reactions • Release energy, usually as: • heat (flame) • light (bioluminescence) • Electricity (battery) • Important ex.: Combustion • What is combustion? • Combustion- oxygen reacts rapidly with another substance, releasing energy (burning) • 2C6H14(l) + O2(g) 12CO2(g) + 14H2O(g) + energy • (Combustion of hexane)

  11. Endothermic Reactions • Absorb energy • Ex. Cold packs- squeeze package, breaks pack inside which keeps chemicals separate; absorb energy and whole mixture cools down • Ex. Photosynthesis • Energy + 6CO2(g) + 6H2O(l) C6H12O6(aq) + 6O2(g)

  12. Biochemical Reactions • They may be endothermic or exothermic • They are almost always helped by enzymes (biological catalysts) • Catalysts are chemicals that speed up a reaction but are not used up by it. • Photosynthesis and Cellular Respiration

  13. Law of Conservation of Mass • Developed by Antoine Lavoisier • Total mass of the reactants equals the total mass of the products • Using this, we can deduce that: • ** total # of atoms present before a reaction equals the total # of atoms after a reaction

  14. Example • If I get 13 g of H2O and 15 g of NaCl from the reaction of HCl and NaOH, how much NaOH did I use, if I used 10 g of HCl? • HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) • 10g ? 13g 15g • Answer: 18 g

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