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Endo and exo rections experiments 14/15

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Endothermic and Exothermic reactions notes with demos.

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Endo and exo rections experiments 14/15

  1. 1. Endothermic and Exothermic Reactions
  2. 2. Physical Change • change in size, shape, color, or state of matter
  3. 3. Chemical Reactions • process in which one or more substances are changed into others. Chemical reactions are accompanied by a loss or gain of energy. • Indicators of chemical changes are evident. Indicators: •Temperature change •Odor change •Formation of a precipitate And sometimes… •Color change
  4. 4. Activation Energy •the smallest amount of energy needed to make a substance react
  5. 5. Exothermic • energy (heat, light, electrical, etc.) is given off; surroundings usually feel warmer - ex. Combustion, evaporation of water
  6. 6. Cellular Respiration Cellular respiration allows organisms to use (release) energy stored in the chemical bonds of glucose (C6H12O6). The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP. This is an example of an exothermic reaction.
  7. 7. Exothermic Diagram Energy level Activation energy Energy given out by Reactants Using a catalyst reaction might lower the activation energy Reaction progress © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910 Products
  8. 8. Salt An example of an exothermic reaction is the mixture of sodium metal and chlorine gas which yields table salt. 2Na(s) + Cl2(g)  2NaCl(s) + energy
  9. 9. Set up your Lab Notebook like this: ___________ Experiment (You’ll fill in the blank after the experiment.) Jar temperature: _____ Temperature of steel wool soaked in vinegar: ________
  10. 10. Experiment Procedures: 1. Place the thermometer in the jar and close the lid. Allow about 5 minutes for the thermometer to record the temperature, then open the lid and remove the thermometer. Take a reading.
  11. 11. Experiment 2. Soak a piece of steel wool in vinegar for 1 minute. 3. Squeeze the excess vinegar out of the steel wool.
  12. 12. Experiment 4. Wrap the wool around the thermometer and place the wool/thermometer in the jar, sealing the lid. 5. Allow 5 minutes, then read the temperature and compare it with the first reading.
  13. 13. Explain 1. Is this an endothermic or exothermic reaction? How do you know? 2. Fill in the blank in your title.
  14. 14. Clean-Up Experiment 1: •Place steel wool in the trash. •Wipe out jar with paper towel. •Replace thermometer in jar and close the lid. •Replenish any materials necessary for next period.
  15. 15. Endothermic • A chemical reaction in which energy is absorbed; surroundings usually feel cooler - ex. Cold packs
  16. 16. Endothermic Diagram Energy Activation energy Energy absorbed by reaction Reaction progress Reactants © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910 Products
  17. 17. How do cold packs work? The outer pouch contains water. The inner pouch contains ammonium-nitrate. When you “pop” the inner pouch, the chemical reaction absorbs heat energy from the surroundings. This is an endothermic reaction. The temperature of the solution falls to about 35 F for 10 to 15 minutes.
  18. 18. Photosynthesis During photosynthesis, plants absorb the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This is an example of an endothermic reaction. sunlight + 6CO2 + 6H2O  C6H12O6 + 6O2
  19. 19. True or False Chemical reactions always produce heat F
  20. 20. Chemical reactions can release or absorb heat, but can also create light, sound, or electricity!
  21. 21. True or False Heat can be lost, destroyed or just disappear F
  22. 22. Heat energy is transferred from one object to another, or is transferred to another form of energy, but never disappears. Law of Conservation of Energy
  23. 23. True or False Color change is always a physical property F
  24. 24. Color is a physical property. Color change can be the result of a chemical change.
  25. 25. Set up your Lab Notebook like this: ________________ Experiment (You’ll fill in the blank after the experiment.) Citric acid solution (H3C6H5O7) temperature: _____ Citric acid + NaHCO3 temperature:___ Reaction time: ___________________
  26. 26. Experiment 1. Pour 25 mL citric acid solution in a Styrofoam cup. Use a thermometer or other temperature probe to record the initial temperature.
  27. 27. Experiment 2. Stir in 15g baking soda (sodium bicarbonate: NaHCO3). Track the change in temperature as a function of time. This means you will start a timer when you add the baking soda. Stop the timer when the temperature no longer changes.
  28. 28. Explain 1. Describe what happens when baking soda and citric acid are mixed. 2. What are evidences of chemical change?
  29. 29. Explain 3. Is this an endothermic or exothermic reaction? How do you know? 4. Fill in the blank in your title.
  30. 30. Clean-Up Experiment 2: •Pour citric acid and baking soda solution into the sink while running water. •Rinse the cup. Place it back at your station for the next class. •Replenish any materials necessary for next period.

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