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Chapter6 - Chapter 6 Thermochemistry Chem 6A Section D 1 1...

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Chem 6A Michael J. Sailor, UC San Diego Chapter 6: Thermochemistry Chem 6A, Section D Oct 11, 2011 1 1 Chem 6A Michael J. Sailor, UC San Diego Announcements: Thurs Oct 13 quiz (#3) will cover chapter 4 Put a box around (or circle) your answers Bring student ID No notes, no calculators 2
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Chem 6A Michael J. Sailor, UC San Diego Quiz 2 score histogram 3 Chem 6A Michael J. Sailor, UC San Diego 4 0 20 40 60 80 100 120 F D C- C C+ B- B B+ A- A A+ number of students Grades so far (after quizzes 1-2)
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Chem 6A Michael J. Sailor, UC San Diego 2 System vs Surroundings Internal energy = E Change in internal energy: Δ E = E final - E initial Sign conventions: Always defined from the system’s perspective Lose energy to the surroundings: Δ E = negative Gain energy from the surroundings: Δ E = positive System is what we are measuring Surroundings is everything outside the system surroundings system Chem 6A Michael J. Sailor, UC San Diego Heat and Work Internal energy ( E) takes the form of either heat (q) or work (w) Change in internal energy: Δ E = q + w Heat (q) = thermal energy; a change in temperature Work (w) = force applied over a distance; mechanical, electrical, etc.
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http://www.hottubenclosure.org/ Chem 6A Michael J. Sailor, UC San Diego Example: Heat and Work Your core body temperature increases by 2°C when sitting in a hot tub. If your body is the system and the hot tub is your surroundings, what are the signs of Δ E , q, and w? System your body Surroundings hot tub heat (q) work (w) Δ E Heat flows from the surroundings to the system and no work is performed www.locomotivesandtrains.com Chem 6A Michael J. Sailor, UC San Diego Example: Heat and Work In one second, the engine in a steam locomotive delivers 2,240 kJ to drive the train forward. In the process, it generates 3700 kJ of heat. If the engine is the system and the locomotive is the surroundings, what are Δ E , q, and w?
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