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Lecture14221
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a supplemental resource for students

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Lecture14221 Presentation Transcript

  • 1. Thermochemistry: Energy, Heat and Work Lecture 14
  • 2. Whenever matters changes, whether physically or chemically, the energy content of the matter changes also.
  • 3. Energy is absorbed and released.
  • 4. Energy is absorbed and released.
  • 5. Some industries manufacture products that
    • release energy (common fuels - natural gas, oil, wood, coal);
    • absorb energy (fertilizers);
    • limit the flow of energy (insulators - plastic, fiberglass, ceramic and other materials).
  • 6. Energy is interconverted.
  • 7.  
  • 8. Solar, electrical, nuclear, chemical, etc. forms of energy are all examples of potential and kinetic energy on the atomic and molecular scales.
  • 9. When energy is transformed from one object to another, it appears as work and/or as heat.
  • 10. A system is a part of the universe that is under consideration.
  • 11. The surroundings is the rest of the universe.
  • 12. Boundary (or wall), real or imaginary, separates the system from the surroundings.
  • 13. The system and the surroundings.
  • 14. The internal energy of the system is the total of the kinetic energy due to the motion of particles and the potential energy associated with their arrangement.
  • 15. The internal energy of the system includes the energy in all the chemical bonds, and the energy of the free, conduction electrons in metals.
  • 16. The internal energy of the system changes as its contents change from reactants to products.
  • 17. The change in the internal energy is determined as a difference between the system’s internal energy after the change and before the change: ΔE = E final – E initial = E products – E reactants
  • 18. ΔE (delta ee:) refers to the final state of the system minus the initial state of the system: ΔE = E final – E initial
  • 19. A change in the energy of the system is always accompanied by an opposite change in the energy of the surroundings.
  • 20. A system can change its internal energy in of two ways:
    • By losing some energy to the surroundings: E final < E initial , ΔE < 0
    • By gaining some energy from the surroundings: E final > E initial , ΔE > 0
    • The change in energy is always a transfer of energy from system to surroundings, or vice versa.
  • 21. Energy transfer diagrams
  • 22. Energy transfer outward from the system or inward from the surroundings can appear in two forms: heat and work .
  • 23. Heat is the energy transferred between a system and its surroundings as a result of difference in their temperatures only.
  • 24. Work is the energy transferred between a system and its surroundings as a result of moving object by a force.
  • 25. The total change in a system’s internal energy is the sum of the energy transferred as heat and/or work: ΔE = q + w
  • 26. The sign of the energy transfer is defined from the system’s prospective. Energy coming into the system is positive . Energy going out from the system is negative .
  • 27. If energy is transferred as heat only
    • and heat is flowing out from a system (blue arrow), its energy decreases until its temperature equals to that of the surroundings: E final < E initial , q is negative, ΔE < 0.
  • 28. If energy is transferred as heat only
    • and heat is flowing into a system (red arrow), its energy increases until its temperature equals to that of the surroundings: E final > E initial , q is positive, ΔE > 0.
  • 29. If energy is transferred as work only
    • and work is done by a system (blue arrow), its energy decreases: E final < E initial because w is negative, ΔE < 0 .
  • 30. If energy is transferred as work only
    • and work is done on a system (red arrow), its energy increases: E final > E initial because w is positive, ΔE > 0 .
  • 31. The sign conventions for q, w, and ΔE:
    • Q + w = ΔE
    • ------------------------------------------------------------
    • + + +
    • + - depends on sizes of q and w
    • + - depends on sizes of q and w
    • - - -
  • 32. THE END