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7.3 Exothermic and Endothermic Reactions

7.3 Exothermic and Endothermic Reactions. Review Stuff from 7.1. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products . Reactants are on the left side Products are on the right side. Law? What law?.

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7.3 Exothermic and Endothermic Reactions

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  1. 7.3 Exothermic and Endothermic Reactions

  2. Review Stuff from 7.1 • Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products. • Reactants are on the left side • Products are on the right side.

  3. Law? What law? • During a chemical reaction, mass is neither created or destroyed. This is defined as……….? Law of Conservation of Mass

  4. Did You Know? • Physical changes can release or absorb energy. VOCABULARY FOR 7.3 • Break down the prefix or root words • Endo = “in” • Exo = “out” • Thermic = “heat”

  5. Exo = “out” • During an exothermic change, such as freezing, energy is released to the surroundings. • The energy released as the products form is more than the energy required to break the bonds in the reactants.

  6. Combustion • An example of an extremely exothermic reaction. • Because heat is released, the energy term appears on the right sideof the equation. • When 1 mole of propane reacts with 5 moles of oxygen, 2220 kJ (kilojoules) of heat is released. • You can use this value to replace “heat” in the combustion equation written earlier.

  7. How to read an exothermic reaction • Cu(s) + Cl2(g) → CuCl2(g) + 220.1 kJ energy is released

  8. Where is the chemical energy is greater? • Cu(s) + Cl2(g) → CuCl2(g) + 220.1 kJ REACTANTS

  9. Endo = “in” • During an endothermic change, such as melting, energy is absorbed from the surroundings. Energy also flows into and out of chemical changes.

  10. Decomposition. • When mercury(II) oxide is heated to a temperature of about 450°C, it breaks down into mercury and oxygen. • The decomposition of mercury(II) oxide is an endothermic reaction that can be described by the following equation. • Because heat is absorbed, the energy term appears on the left sideof the equation. • For every 2 moles of HgO that decomposes, 181.7 kJ of heat must be absorbed.

  11. How to read an endothermic reaction • H2O(g) + C(s) + 132 kJ → CO2(g) + 2H2(g) energy is absorbed

  12. Where is the chemical energy is greater? • H2O(g) + C(s) + 132 kJ → CO2(g) + 2H2(g) PRODUCTS

  13. Exothermic and Endothermic Reactions (run time 55 seconds)

  14. Identify the reactions below. • CH4(s) + 2O2(g) → CO2(g) + 2H2O(l) ΔH° = -890 kJ • 2HCl(g) → H2(g) + Cl2(g) ΔH° = 185 kJ • 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) ΔH° = -1169 kJ Endothermic Exothermic Endothermic

  15. Practice Problems • When potassium nitrate dissolves in water, the beaker containing the solution gets cooler. • Is dissolving this salt an exothermic or an endothermic process? Endothermic The reaction requires heat, which it absorbs from the surroundings (the water). This causes the water temperature to decrease.

  16. Practice Problems Endothermic This reaction cn be identified as……. Exothermic

  17. Which graph would represent burning of wood in a bonfire?

  18. Which graph would represent the melting of ice?

  19. Exothermic and Endothermic Changes (run time 9:08)

  20. The ENDo Ha ha – get it?

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