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CH 301 Chapter 6 notes part 1v2

CH 301 Chapter 6 notes part 1v2 - CH301 Notes Chapter 6...

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CH301 Notes Chapter 6 part 1 Thermodynamics - study of the changes or transfers in energy accompanying chemical and physical processes. Will two (or more) substances react when mixed under specified conditions? What energy changes and transfers are associated with this? How far does the reaction occur? Thermodynamic Terms system: region of interest, or, substances involved in the chemical and physical changes. In lab, its the chemicals inside the beaker. surroundings: environment around the system - where observations are made. system + surroundings = universe . Types of Systems: depends on how energy and/or matter is exchanged with surroundings: OPEN: exchange energy & matter CLOSED: exchange energy only. ISOLATED: NO exchange (energy or matter) WORK: Motion against an opposing force. WORK = FORCE x DISTANCE Types: UNITS: Joule, J 1J = 1kg m 2 s -2 Expansion (expansion against an external force) Nonexpansion (work is done but there is no expansion against an external force) INTERNAL ENERGY, U: Total energy inside system (can be used to do work) We NEVER know the absolute value of U – dont know exact energy of all component particles We CAN find the CHANGE in U: CHANGE in X is always given by: Δ X = X (final) - X (initial) Internal Energy and Work: If work done on system: ( energy in form of work transfers to system from surroundings ) w is positive, so is U: system’s internal energy increases by: Δ U = w Assumes NO other type of energy transfer occurred! If work done by system on surroundings: w is negative, Δ U is negative, system lost energy. Expansion Work against a Constant External Pressure System: Piston, area A: pushes against external (surrounding) pressure P ext ; experiences opposing force f = P ex A Move piston out a distance d : Work done by system on surroundings: system loses energy: Work = d P ex A But d A = Δ V so w = - P ex Δ V P ex MUST BE CONSTANT! Expansion Work Against a Vaccum P ex = zero so w = zero! FREE EXPANSION- No expansion work done by system- no energy lost. Getting Units to Work Out: If P is in Pa (1Pa = 1kg m -1 s -2 ) and Δ V is in m 3 , get w in J.
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