Unit 3, chap 9

# Unit 3, chap 9 - Chapter 9 Energy must always be conserved...

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Chapter 9

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Energy must always be conserved It can be converted from one form to another, but cannot be created or destroyed Ball A has PE because of its higher position When ball A is released, PE is converted to KE as it rolls downhill When it hits ball B, KE A is converted to KE B Ball B loses KE as it rolls uphill, gaining PE
Energy is defined as the capacity to do work or to produce heat Mathematically stated, Δ E = w + q Work (w) is a force acting over a distance Work was done when ball A was placed in the initial higher position Heat (q) is the transfer of energy between two objects due to a temperature difference Ball A and B will eventually slow to a stop because some KE is transferred to the hill as heat, due to friction

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Change in energy is a state function - it depends only on the present state of the system, it is independent of the pathway Ball A is going to transfer the same amount of energy every time it is dropped ( Δ E is the same no matter what the pathway) Work and heat are not state functions The way the energy transfer is divided between work and heat depends on the conditions (more energy is transferred to frictional heat on a bumpy hill so there is less energy available to do work on ball B)
All state functions are independent of the path taken to reach the present state Δ X = X final – X initial where X is any state function P, V, a n d T a r e s t a t e f u n c t i o n s w e ’ v e s e e n Internal energy, enthalpy, entropy, and free energy are state functions we’ll see in this chapter Heat and work are not state functions

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A system is the part of the universe on which we want to focus our attention The surroundings are everything else Energy is exchanged between the system and surroundings Δ E system = - Δ E surroundings
Example: If 1200 J of heat are added to a system, then the system does 800 J of work on the surroundings, what is the change in energy for the system? The surroundings?

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## This note was uploaded on 07/25/2011 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.

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Unit 3, chap 9 - Chapter 9 Energy must always be conserved...

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