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CHAPTER TWO

THERMODYNAMIC PROPERTIES, PROPERTY RELATIONSHIPS, AND PROCESSES

LEARNING OBJECTIVES

After studying Chapter 2, you should:
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Be able to explain the meaning of the continuum limit and its importance to thermodynamics. Be familiar with the following basic thermodynamic properties: pressure, temperature, specific volume and density, specific internal energy and enthalpy,constant-pressure and constant-volume specific heats, entropy, and Gibbs free energy. Understand the relationships among absolute, gage, and vacuum pressures. Know the four common temperature scales and be proficient at conversions among all four. Know how many independent intensive properties are required to determine the thermodynamic state of a simple compressible substance. Be able to indicatewhat properties are involved in the following state relationships: equation of state, calorific equation of state, and the Gibbs (or T–ds) relationships. Explain the fundamental assumptions used to describe the molecular behavior of an ideal gas and under what conditions these assumptions break down.

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Be able to write one or more forms of the ideal gas equation of state and from thisderive all other (mass, molar, mass-specific, and molarspecific) forms. Be proficient at obtaining thermodynamic properties for liquids and gases from NIST software or online databases and from printed tables. Be able to explain in words and write out mathematically the meaning of the thermodynamic property quality. Be able to draw and identify the following on T–v , P–v , and T–s diagrams: saturatedliquid line, saturated vapor line, critical point, compressed liquid region, liquid–vapor region, and the superheated vapor region. Be able to draw an isobar on a T–v diagram, an isotherm on a P–v diagram, and both isobars and isotherms on a T–s diagram. Be proficient at plotting simple isobaric, isochoric, isothermal, and isentropic thermodynamic processes on T–v , P–v , and T–s coordinates. Beable to explain the approximations used to

estimate properties for liquids and solids.
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Be able to derive all of the isentropic process relationships for an ideal gas given that Pv g constant. Be able to explain the meaning of a polytropic process and write the general state relationship expressing a polytropic process. Be able to explain the principle of corresponding states and the useof generalized compressibility charts. Be able to express the composition of a gas mixture using both mole and mass fractions. Be able to calculate the thermodynamic properties of an ideal-gas mixture knowing the mixture composition and the properties of the constituent gases. Understand the concept of standardized properties, in particular, standardized enthalpies, and their application toideal-gas systems involving chemical reaction. Be able to apply the concepts and skills developed in this chapter throughout this book.

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Chapter 2 Overview
THIS IS ONE OF THE LONGER chapters in this book and should be revisited many times at various levels. To cover in detail the subject of the properties of gasesand liquids would take an entire book. Reference [1] is a classic example of such a book. We begin our study of properties by defining a few basic terms and concepts. This is followed by a treatment of ideal-gas properties that originate from the equation of state, calorific equations of state, and the second law of thermodynamics. Various approaches for obtaining properties of nonideal gases,liquids, and solids follow. The properties of substances that have coexisting liquid and vapor phases are emphasized. The concept of illustrating processes graphically using thermodynamic property coordinates (i.e., T–v , P–v , and T–s coordinates) is developed. In addition to dealing with pure substances, we treat the thermodynamic properties of nonreacting and reacting ideal-gas mixtures. The...