chap 3 - CHAPTER CHAPTER Properties of Pure Substances 1...

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HAPTER CHAPTER Properties of Pure Substances 1
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tate changes during a process Why do we need to deal with the properties of a system ? The P-V diagram of a compression process. State changes during a process A state is characterized by Its properties . So properties go through changes during a process where energy onversion and conversion and transfer take place . There are different paths between State 1 and State 2. 2
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1 Pure Substance § 3.1 Pure Substance ure substance the one with • Pure substance : the one with homogeneous and invariable ( fixed) chemical composition . Chemical composition – Water : H 2 O Air : O 2 +N 2 Methane : CH 4 3
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A mixture of O 2 +N 2 various chemical lements or elements or compounds also ualifies as a qualifies as a pure substance as long as the mixture is homogeneous .g, air). (e.g, air). 4
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§ 3.1 Phases of A Pure Substance hree principal phases olid uid and Three principal phases solid , liquid , and gas , each with a different molecular structure. hase having a distinct molecular • Phase : having a distinct molecular arrangement that is homogeneous roughout and separated from the others by throughout and separated from the others by easily identifiable boundary surfaces. • Solid : arranged in a three-dimensional pattern (lattice) that is repeated throughout. 5
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§ 3.1 Phases of A Pure Substance iquid molecular spacing is not much Liquid : molecular spacing is not much different from that of the solid phase, xcept the molecules are no longer at except the molecules are no longer at fixed positions. as the molecules are far apart from • Gas : the molecules are far apart from each other, and a molecular order is onexistent nonexistent. 7
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A mixture of two or more phases of a pure ubstance is still a ure substance s long as the substance is still a pure substance as long as the chemical composition of all phases is the same. hase of a pure substance very pure substance has Phase of a pure substance – every pure substance has three potential phases Gas, Liquid and Solid Vapor Gas Atm. Air ,q Liquid Liquid Air O 2 +N 2 H 2 O Water H 2 O Air oth chambers are pure substances O 2 +N 2 H 2 O Both chambers are pure substances 9
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§ 3.2 Vapor-Liquid-Solid Phase Equilibrium in a Pure Substance e and water in an Ice and water in an isolated system (no mass nor energy Exchange with the Surroundings) will co-exist thermal and mechanical In thermal and mechanical equilibrium (uniform T and P) 10
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§ 3.2 Phase-change Processes of pure Substances Vapor phase Water to steam pp Liquid phase Condenser Steam to water 11
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Let us first perform a simple familiar experiment Boil water under a constant pressure he piston has a fixed weight The piston has a fixed weight That maintains a constant pressure P system = constant System 12
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T system = constant = saturation temperature orresponding to pressure corresponding to pressure 15
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pressure increase 18
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creases with P T SAT increases with P 20
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Denver elevation = 1600 m, P = 83 kPa, BT= 94 C 21
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§ 3.2 Phase-change Processes of pure Substances • Focus on the
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This note was uploaded on 09/27/2011 for the course EML 3100 taught by Professor Sherif during the Fall '08 term at University of Florida.

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chap 3 - CHAPTER CHAPTER Properties of Pure Substances 1...

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