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# Lecture15221

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### Lecture15221

1. 1. Thermochemistry: the Law of Energy Conservation Lecture 15
2. 2. When a system gains energy, the surroundings lose it.
3. 3. When a system loses energy, the surroundings gain it.
4. 4. Energy is conserved: it may be converted from one form to the other but it is not destroyed.
5. 5. <ul><li>Julius Robert von Mayer (1814-1878), German scientist </li></ul>
6. 6. Energy flow in a car:
7. 7. Energy flow via photosynthesis
8. 8. Total energy flow
9. 9. The first law of thermodynamics: the total energy of the Universe is constant.
10. 10. The energy of the system plus the energy of the surroundings remains constant: energy is conserved. ΔE universe =ΔE system + ΔE surroundings
11. 11. Units of energy
12. 12. <ul><li>James Prescott Joule (1818-1889), British scientist </li></ul>
13. 13. A sample problem on determining the change in internal energy of a system.
14. 14. There is no particular sequence by which the internal energy (E) of a system must change.
15. 15. Internal energy E is a state function, a property dependent only on the current state of the system, not on the path the system took to reach that state.
16. 16. By state of the system we mean its composition, volume, pressure, and temperature.
17. 17. Different paths, same change:
18. 18. ΔE does not depend on how the change takes place.
19. 19. Even though the separate quantities of work and heat available from the change do depend on how the change occurs, ΔE does not.
20. 20. ΔE (sum of q and w) is constant for a given change, even though q and w can vary.
21. 21. Heat and work are not state functions because their values do depend on the path the system takes in undergoing the energy change.
22. 22. Volume and temperature are state functions because their values do not depend on the path the system takes to reach them.
23. 23. Symbols for state functions E, P, V, ΔE, ΔP, ΔV are capitalized.
24. 24. THE END