Chapter_3

# Chapter_3 - Student Study Guide for 5th edition of...

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Student Study Guide for 5 th edition of Thermodynamics by Y. A. Ç engel & M. A. Boles 3- 1 Chapter 3-1 Chapter 3: Properties of Pure Substances We now turn our attention to the concept of pure substances and the presentation of their data. Simple System A simple system is one in which the effects of motion, viscosity, fluid shear, capillarity, anisotropic stress, and external force fields are absent. Homogeneous Substance A substance that has uniform thermodynamic properties throughout is said to be homogeneous. Pure Substance A pure substance has a homogeneous and invariable chemical composition and may exist in more than one phase. Examples: 1. Water (solid, liquid, and vapor phases) 2. Mixture of liquid water and water vapor 3. Carbon dioxide, CO 2 4. Nitrogen, N 2 5. Mixtures of gases, such as air, as long as there is no change of phase. State Postulate Again, the state postulate for a simple, pure substance states that the equilibrium state can be determined by specifying any two independent intensive properties.

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Student Study Guide for 5 th edition of Thermodynamics by Y. A. Ç engel & M. A. Boles 3- 2 Chapter 3-2 The P-V-T Surface for a Real Substance P-V-T Surface for a Substance that contracts upon freezing P-V-T Surface for a Substance that expands upon freezing
Student Study Guide for 5 th edition of Thermodynamics by Y. A. Ç engel & M. A. Boles 3- 3 Chapter 3-3 Real substances that readily change phase from solid to liquid to gas such as water, refrigerant-134a, and ammonia cannot be treated as ideal gases in general. The pressure, volume, temperature relation, or equation of state for these substances is generally very complicated, and the thermodynamic properties are given in table form. The properties of these substances may be illustrated by the functional relation F ( P , v , T )=0, called an equation of state. The above two figures illustrate the function for a substance that contracts on freezing and a substance that expands on freezing. Constant pressure curves on a temperature-volume diagram are shown in Figure 3- 11. These figures show three regions where a substance like water may exist as a solid, liquid or gas (or vapor). Also these figures show that a substance may exist as a mixture of two phases during phase change, solid-vapor, solid-liquid, and liquid-vapor. Water may exist in the compressed liquid region, a region where saturated liquid water and saturated water vapor are in equilibrium (called the saturation region), and the superheated vapor region (the solid or ice region is not shown). Let's consider the results of heating liquid water from 20 ° C, 1 atm while keeping the pressure constant. We will follow the constant pressure process shown in Figure 3-11. First place liquid water in a piston-cylinder device where a fixed weight is placed on the piston to keep the pressure of the water constant at all times. As liquid water is heated while the pressure is held constant, the following events occur.

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Chapter_3 - Student Study Guide for 5th edition of...

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