chapter1 - Chapter 1 Review of the First and Second Laws of...

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Chapter 1 Review of the First and Second Laws of Thermodynamics The purpose of this chapter is twofold: ( i ) to summarize the de f nitions and concepts used in thermodynamics, ( ii ) to explain what the f rst and second laws of thermodynamics are and show how to simplify the equations expressing these laws for various systems. 1.1 DEFINITIONS 1.1.1 System Any region which occupies a volume and has a boundary is called a system .T h ev o l u m e outside the boundary is called the surroundings of the system. The sum of the system and its surroundings is called the universe . Thermodynamics considers systems only at the macroscopic level. It is convenient to distinguish between three general types of systems. Isolated system : These are the set of systems which exchange neither mass nor energy with the surroundings. For example, the universe is an isolated system. Closed system : These are the set of systems which exchange energy (in the form of heat and work) but not mass with the surroundings. Open system : These are the set of systems which exchange both mass and energy with the surroundings. The equations available to analyze closed and open systems are di f erent from each other. Therefore, one should properly de f ne the system before solving the problem. 1.1.2 State In order to describe and analyze a system, some of the quantities that are characteristic of it must be known. These quantities are called properties and include volume, mass, temperature, pressure, etc. A complete list of the properties of a system describes its state . Consider a function w = f ( x, y ) (1.1-1) in which there are three variables: w is dependent, x and y are independent. In thermodynamics we would say that " the state of the system, w ,is f xed when the thermodynamic properties x and y are speci f ed ." Note that the mathematical term "point" is equivalent to the thermodynamic term "state". A change of state is called a
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1.1.3 Intensive and Extensive Properties Thermodynamic properties are considered to be either intensive or extensive . When the prop- erty is proportional to the mass of the system, the property is extensive , i.e., volume, kinetic energy, potential energy. On the other hand, when the property is independent of the mass of the system, the property is intensive , i.e., viscosity, refractive index, density, temperature, pressure, mole fraction. Speci f c (or molar) properties are extensive properties divided by the total mass (or total moles) of the system, i.e., Speci f cproperty = Extensive property Total mass Molar property = Extensive property Total moles (1.1-2) If ϕ represents any extensive property, then Eq. (1.1-2) is expressed as b ϕ = ϕ m and e ϕ = ϕ n (1.1-3) where m and n are the total mass and moles, respectively. Note that all speci
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This note was uploaded on 04/06/2010 for the course CHE 327 taught by Professor Ozbelge during the Spring '10 term at Middle East Technical University.

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chapter1 - Chapter 1 Review of the First and Second Laws of...

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