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Thermodynamics1 - Thermodynamics I T h e F ir s t L a w A S...

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Page ‹#› I. The First Law A. Statement: 1. The energy of the universe is constant. 2. or... “that’s all there is, there ain’t no more! 3. or energy can only be transformed between system & surroundings . Thermodynamics So what is Energy? Working Definition: Ability to do work or produce heat. Thermodynamics ! Mechanical Potential - position ( m • g • h) Kinetic - motion ( 1/2 • m • V 2 ) ! Chemical - energy of bonds made and bonds broken ! Electrical - energy of electron transfer Thermodynamics Law of Conservation of Energy: In an ordinary process, energy must be conserved ! So ??? We can only TRANSFER energy! Thermodynamics ! Mechanical--Potential -> Kinetic ! Heat - Another way to transfer energy. - A result of a difference in T. Thermodynamics POTENTIAL KINETIC B. Terms 1. heat (q) - one form of energy that is transferred between two objects due to a ! T. 2 . . work (w) - the other form of energy -something gets MOVED Thermodynamics
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Page ‹#› 3. UNITS- Joule - the SI unit by which we measure energy changes. Work is a force applied through a distance. (W = F x s) and F = ma SO W = m • a • s 1 Joule = 1 kg • m/s 2 • m or 1 kg m 2 /s 2 = 1 N - m also equivalent to: 0.239 calories Thermodynamics 4. system - something in which we’re interested, e.g. reaction 5. surroundings- everything else OUTSIDE the system System =(Universe - Surroundings) surroundings system Thermodynamics 6. ! E ! the change in internal energy that occurs as a result of a physical or chemical process 7. State functions - properties that are pathway independent Represented with CAPITAL letters: E, H, S, G vs q,w Thermodynamics C. Conventions System Surroundings q = + q = - w = - w = + Thermodynamics D. Defining Relationship Recognizing only q and w as forms of energy, then ! E = q + w or... the total energy change of a system is equal to the heat absorbed by the system PLUS the work done on the system. Thermodynamics E. ! E explored -- Types of Processes a. Constant Volume: ( ! V ! 0) so ! E = q + w = q +(- P ! V) = q Thermodynamics
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Page ‹#› E. ! E explored -- Types of Processes a. Constant Volume: ( ! V ! 0) so ! E = q + w = q v + (-P ! V) = q v b. Constant Pressure - most common - w is " 0 ( ! V typically " 0) - open containers Thermodynamics b. Constant Pressure - w is " 0 ( ! V typically " 0) Calculate the work done by a gas as it expands from 46 L to 64 L at a constant pressure of 15 atm .
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