Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- THERMODYNAMICS: Fundamental for Applications
- 0 Introduction
- PART I THE BASICS
- 1 Primitives
- 2 The First and Second Laws
- 3 Fundamental Relations
- PART II SINGLE-PHASE SYSTEMS
- PART III MULTIPHASE AND REACTING SYSTEMS
- PART IV ENGINEERING CALCULATIONS
- APPENDICES
- Notation
- Index
3 - Fundamental Relations
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Acknowledgments
- THERMODYNAMICS: Fundamental for Applications
- 0 Introduction
- PART I THE BASICS
- 1 Primitives
- 2 The First and Second Laws
- 3 Fundamental Relations
- PART II SINGLE-PHASE SYSTEMS
- PART III MULTIPHASE AND REACTING SYSTEMS
- PART IV ENGINEERING CALCULATIONS
- APPENDICES
- Notation
- Index
Summary
In the previous chapter we accomplished our first objective: we showed how the process variables heat and work are related to changes in system properties, the internal energy U and the entropy S. Those relations are provided by the first and second laws. Now our problem is to learn how to compute changes in U and S. Since U and S cannot be obtained directly from experiment, we must first relate ΔU and ΔS to measurable state functions, particularly temperature, pressure, volume, composition, and heat capacities. When we can establish such relations, our strategy in a process analysis can take the path on the left branch of the diagram shown in Figure 3.1.
Unfortunately, ΔU and ΔS are not always simply related to measurables, nor are ΔU and ΔS always directly related to convenient changes of state. So to ease conceptual and computational difficulties, we create additional state functions. Then we must establish how ΔU and ΔS are related to these new state functions and, in turn, how changes in the new functions are related to measurables. In these situations, our strategy follows the right branch of the diagram in Figure 3.1. In this chapter we develop relations that allow us to follow both strategies represented in the figure.
Our long-term goal is to be able to analyze processes, and since processes cause changes in system states, we begin by discussing the conditions that must be satisfied to characterize a state (§ 3.1).
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- Chapter
- Information
- ThermodynamicsFundamentals for Applications, pp. 69 - 118Publisher: Cambridge University PressPrint publication year: 2005