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Properties of a Pure Substance. 3-1 The Pure Substance A pure substance is one that has a homogeneous and invariable chemical composition. It may exist.

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Presentation on theme: "Properties of a Pure Substance. 3-1 The Pure Substance A pure substance is one that has a homogeneous and invariable chemical composition. It may exist."— Presentation transcript:

1 Properties of a Pure Substance

2 3-1 The Pure Substance A pure substance is one that has a homogeneous and invariable chemical composition. It may exist in more than one phase, but the chemical composition is the same in all phases.

3 3-2 Vapor-Liquid-Solid-Phase Equilibrium in a Pure Substance

4 Saturation Temperature and Saturation Pressure The term saturation temperature designates the temperature at which vaporization takes place at a given temperature. This pressure is called the saturation pressure for the given temperature. Saturated liquid or saturated vapor, subcooled liquid or compressed liquid, and superheated vapor.

5 Vapor-Pressure Curve of a Pure Substance

6 Temperature-Volume Diagram

7 Some Critical-Point Data

8 T-v Diagram

9 The Quality Specific Volume Relation (1/2)

10 The Quality Specific Volume Relation (2/2) where : quality or dryness

11 Some Triple-Point Data

12 P-T Diagram of Water

13 CO 2 Phase Diagram

14 H 2 O Phase Diagram

15 3-3 Independent Properties of a Substance The state of a simple pure substance is defined by two independent properties. In a saturation state, pressure and temperature are not independent properties.

16 3-4 Tables of Thermodynamic Properties

17 3-5 Thermodynamic Surfaces Expand on freezing Contract on freezing

18 P-V-T Surface for a Substance that Expands on Freezing (1/2)

19 P-V-T Surface for a Substance that Expands on Freezing (2/2)

20 P-V-T Surface for a Substance that Contracts on Freezing (1/2)

21 P-V-T Surface for a Substance that Contracts on Freezing (2/2)

22 3-6 The P-V-T Behavior of Low-and Moderate –Density Gases At very low densities the average distances between molecules is so large that the intermolecular potential energy may effectively be neglected. In such a case, the particles would be independent of one another, a situation referred to as an ideal gas.

23 The Ideal Gas Equation of State (1/2) : the universal gas constant

24 The Ideal Gas Equation of State (2/2) R : the gas constant

25 T-v Diagram for Water

26 Compressibility Factor Z for ideal gas

27 Compressibility of N 2

28 Observations from Figure 3.15 At all temperatures as. At the temperatures of 300K and above the compressibility factor is near unity up to pressure of about 10MPa. At lower temperatures or at very high pressure, the compressibility factor deviates significantly from the ideal-gas value.

29 Reduced Properties : reduced pressure : reduced temperature : critical pressure : critical temperature

30 The Benedict-Webb-Rubin Equation of State

31 Lee-Kesler Simple Fluid Compressibility Factor


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