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T h e r m o c h e m i s t r y

T h e r m o c h e m i s t r y. The study of energy transfers and chemical reactions. Definitions + Main Ideas. Energy is the ability to do work. Work equals Force times distance System is what we are considering like the beaker, the calorimeter, the flask.

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T h e r m o c h e m i s t r y

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  1. Thermochemistry The study of energy transfers and chemical reactions

  2. Definitions + Main Ideas Energy is the ability to do work. Work equals Force times distance System is what we are considering like the beaker, the calorimeter, the flask. Can be OPEN which means energy can be transferred or exchanged with surroundings Or CLOSED which mean energy stays within the system (theoretically) • The First Law of Thermodynamics States: • Energy can neither be created nor destroyed but may be transformed from one form to another • aka-LAW of Conservation of Energy

  3. What are some forms of Energy? • Electricity • Mechanical • Wind, hydro, rock rolling • Light (aka electromagnetic radiation) • Nuclear (alpha beta gamma) • Xrays, radiowaves, microwaves • Heat (thermal) • Potential or Kinetic? • Potential means stored or the ability to do work because of position or composition • Kinetic means “in motion”

  4. Chem Is Try • Chemical energy is stored (potential) in the form of “bonds.” • Chemical energy is released in the forms of heat, light, and mechanical energy (can you say explosions?)

  5. Kinetic Energy = Physics + Chemistry KE = ½ mv2 • Don’t worry, no problems with this formula ‘til next year. • But we’ll have more Chemistry formulas coming up! • The HEAT changes that accompany chemical changes are Kinetic in Nature. • What is the definition of temperature?

  6. Potential Energy • This graph shows how the potential energy changes as a function of distance between atoms. • When the potential energy is at its lowest, the bond is more stable.

  7. Bonding and Stability • Because atoms are most stable when their outer shells are filled with electrons, forming bonds usually releases energy, and is exothermic. • Breaking bonds requires energy and is endothermic. • Remember exothermic means energy is released to the surroundings or “given off,” exiting the system. • Endothermic means energy is absorbed from the surroundings as the process occurs. It gets “colder.”

  8. Comparing Endothermic Exothermic thermite • Dissolving ammonium nitrate

  9. A few links to look at • http://www.youtube.com/watch?v=idxf-4BKRAI • This summarizes the main differences between endo- and exothermic reactions. Get ready to TAKE NOTES! • What is the painting that appears to be growing out of his head? Look for Dr. B’s comments on the sites. • http://www.youtube.com/watch?v=cBy4Q6A8Hfw • This demonstrates both an endothermic and exothermic change. • Get ready to TAKE NOTES!

  10. A couple more • http://www.youtube.com/watch?v=5RJLvQXce4A • This shows an example of an excellent endothermic chemical reaction. How cool is that? • He introduces a new term: Entropy. We’ll get back to that. • http://www.youtube.com/watch?v=M3ZkoNF2ybg • This shows a compilation of THERMITE reactions. • Thermite reactions are very popular for demonstrating exocharmic reactions. • Sorry I’m not there to do one live for you.

  11. Three ways for heat to flow but always from High to Low T. • Convection • Conduction • Radiation • Review: • Which is between solids, like metals? • Which occurs as a result of fluid movement in gases and liquids? • Which is the result of electromagnetic radiation?

  12. Section 3 Enthalpy in Reactions

  13. http://science.widener.edu/svb/tutorial/thermoequationscsn7.htmlPractice some thermochemical equations See how many you can get correct.

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