第二章 The First Lw of Thermodynamics.pdf - Chapter 2 The First Lw of Thermodynamics 2.1 Introduction Energy • Many Different Forms Kinetic

第二章 The First Lw of Thermodynamics.pdf - Chapter 2...

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Chapter 2 The First Lw of Thermodynamics
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Energy Many Different Forms Kinetic Internal Potential Mechanical Chemical Electrical 2.1 Introduction
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2.1 Introduction Energy The ability to do work. Can be converted or transported. Cannot be created or destroyed. Kinetic Energy --- Energy of motion. K.E. = 1/2 m V 2 Potential Energy --- Energy of position in a potential field. P.E. = m g.h + ...
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2.1 Introduction Potential vs. Kinetic energy Potential energy, as the name implies, is energy that has not yet been used, thus the term potential. Kinetic energy is energy in use (or motion). A tank of gasoline has a certain potential energy that is converted into kinetic energy by the engine. When the potential is used up, you're outta gas! Batteries, when new or recharged, have a certain potential. When placed into a tape recorder and played at loud volume (the only settings for such things), the potential in the batteries is transformed into kinetic energy to drive the speakers. When the potential energy is all used up, the batteries are dead. In the case of rechargeable batteries, their potential is reelevated or restored.
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2.1 Introduction What is Internal Energy ( U ) ?
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2.1 Introduction Internal Energy (U) U ( V,T ) , U ( P,T ) , or U ( P,V ), can take on a number of forms • Kinetic energy of molecules in system. • The potential energy of the constituents of the system relative to the center of mass of the system. For example, a crystal consisting of dipolar molecules will experience a change in its potential energy as an electric field is applied to the system. • The internal energy stored in the form of molecular vibration and rotation. • The internal energy stored in the form of chemical bonds that can be released through a chemical reaction. Internal Energy ( U ) --- Energy associated with the condition of matter, not its motion or position. Internal Energy ( U ) --- kinetic + potential energy of the molecules or atoms of a body.
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2.1 Introduction Internal energy is the energy stored in material systems. 􀂉 Potential energy : interaction energy between electrons, ions, atoms, and molecules 􀂉 Kinetic energy : translational, vibrational, and rotational energy of electrons, ions, atoms, and molecules 􀂉 U is an extensive function of state 􀂉 U = nu(T, P, composition) 􀂉 U always increases with temperature (T) of the system.
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2.1 Introduction First Law of Thermodynamics
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2.1 Introduction The First Law of Thermodynamics is based on our experience that energy can neither be created nor destroyed, if both the system and the surroundings are taken into account. The internal energy, U, of an isolated system is constant. Δ U total U system U surroundings =0 Δ U system =−Δ U surroundings U can be changed by either heat transfer or by work “flow” Δ U = q + w First Law = Conservation of energy: “The total energy (sum of all forms of energy including q and U) of an isolated system is conserved.”
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