Chapter6

Chapter6

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Unformatted text preview: 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 Chem 6A Michael J. Sailor, UC San Diego Quiz 2 score histogram 3 Chem 6A Michael J. Sailor, UC San Diego Grades so far (after quizzes 1-2) number of students 120 100 80 60 40 20 0 F D C- C C+ B- B B+ A- A A+ Chem 6A Michael J. Sailor, UC San Diego 4 System vs Surroundings System is what we are measuring Surroundings is everything outside the system Internal energy = E Change in internal energy: ΔE = Efinal - Einitial system surroundings Sign conventions: Always defined from the system’s perspective Lose energy to the surroundings: ΔE = negative Gain energy from the surroundings: ΔE = positive 2 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: ΔE = q + w Heat (q) = thermal energy; a change in temperature Work (w) = force applied over a distance; mechanical, electrical, etc. 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 ΔE, q, and w? System Surroundings your body hot tub heat (q) q > 0 (+) work (w) w=0 ΔE http://www.hottubenclosure.org/ ΔE > 0 (+) Heat flows from the surroundings to the system and no work is performed 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 ΔE, q, and w? System Surroundings steam engine locomotive heat (q) q = -3,700 J work (w) w = -2,240 J ΔE www.locomotivesandtrains.com ΔE -5,940 J Heat flows from the system to the surroundings and work is performed on the surroundings Chem 6A Micha...
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This note was uploaded on 11/16/2011 for the course CHEM 6A taught by Professor Pomeroy during the Spring '08 term at UCSD.

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