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# CH7Notes - Chapter Seven Thermodynamics The First Law CHEM...

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Chapter Seven Thermodynamics: The First Law CHEM 1211K Fall 2010 1

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Objectives Understand and calculate heat and work Understand the principles behind expansion work Explore the measurement of heat Explore heat transfer at constant pressure and heat capacity at constant pressure and constant volume Understand the enthalpy of physical change and interpret heating curves Explore the relationship between enthalpy and internal energy Understand and use standard reaction enthalpies and enthalpies of formation. 2
Key Ideas Heat and work are equivalent ways of transferring energy between a system and its surroundings. The total energy of an isolated system is constant. The enthalpy change for a process is equal to the heat released at constant pressure. 3

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Why is it important? The laws of thermodynamics govern chemistry and life. They explain why reactions take place and let us predict how much heat reactions release and how much work they can do. Thermodynamics plays a role in every part of our lives. The energy released as heat can be used to compare fuels, and the energy resources of food are used to assess its nutritional value. 4
Introduction Thermodynamics is the study of the transformations of energy from one form into another. The first law of thermodynamics The second law of thermodynamics 5

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Two fundamental concepts of thermodynamics are heat and work . 6 Introduction
Systems (7.1) To keep track of changes in energy, we divide the world into two parts: System Surroundings System + surroundings = 7 Figure 7.3

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A system can be: Open Closed Isolated 8 Systems (7.1) Figure 7.4
Section summary: In thermodynamics, the universe consists of a system and its surroundings. An open system can exchange both matter and energy wit the surroundings. A closed system can exchange only energy. An isolated system can exchange nothing. 9 Systems (7.1)

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Work and Energy (7.2) Work (w) is the process of achieving motion against an opposing force. Work = opposing force x distance moved 10
Energy is the capacity of a system to do work (at least, that’s one definition of it!). The total store of energy in a system is called its internal energy ( U ). 11 Work and Energy (7.2)

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Throughout thermodynamics: D X = X final - X initial D U = U final - U initial 12 Work and Energy (7.2)
If no other type of transfer of energy takes place, then: D U = w 13 Work and Energy (7.2)

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Section summary: Work is the transfer of energy to a system by a process that is equivalent to raising or lowering a weight. For work done on a system, w>0 (w = +) For work done by a system, w<0 (w = -) The internal energy of a system may be changed by doing work. In the absence of other changes,
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CH7Notes - Chapter Seven Thermodynamics The First Law CHEM...

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