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F09_230_L07pre

# F09_230_L07pre - CHEM 230 F09 Lecture 7 Chapter 6...

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CHEM 230 F09 Lecture 7 Chapter 6: Thermodynamics First Law Session ID: 230

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Thermodynamics = study of energy consevation Work free expansion (no work done against a vacuum) no volume change w =0 irreversible: w = -P V work at constant pressure reversible: w = -nRTln(V 2 /V 1 ) *constant temperature *allows you to find maximum work at changing pressure First Law Surroundings, Systems, Exchanges Heat signs, units (cal) Enthalpy Heat Capacity
Energy exchanges Internal Energy (of a system) = U Measure U from perspective of the system. + U = gain energy of system - U = loss of energy from system

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First Law The internal energy (U) of an isolated system is constant. U = q +w Energy is a state function -it depends only on the state and not how it got there (so are T, P, V) Energy as work (w) Energy as heat (q)
Concept Question Hiker #1 and Hiker #2 start from the same point on a hill, but take different paths down to the 100 m marker. Hiker #1 takes a path that is 200 m long. Hiker #2 takes a path that is 300 m long. Which of the following would not be a state function? A. Their mass B. The height they climbed C. The force of gravity, g D. The distance they walked E. None of the above

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First Law For all systems and surroundings, the heat from or work done on the system is the opposite of the heat from or work done on the surroundings: q surroundings = -q system w surroundings = -w system In a reversible system, maximum work performed In an irreversible system, some work performed http://www.chem1.com/acad/webtext/thermeq/TE2.html#1C
Concept Question Two identical engines of the same consume the same quantity of energy. After 10 minutes they are stopped and the temperature of the oil is taken. The oil from engine #1 is 80 o C. The oil from engine #2 is 90 o C. Which engine is performing more work?

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