Page 24 - Physical chemistry eng

1 CHAPTER

Fundamental 1.1 What Is Thermodynamics
and Why Is It Useful?
Concepts of 1.2 The Macroscopic Variables
Volume, Pressure, and
Temperature
Thermodynamics 1.3 Basic Definitions Needed to
Describe Thermodynamic
Systems
1.4 Equations of State and the
Ideal Gas Law
1.5 A Brief Introduction to
Thermodynamics provides a description of matter on a macroscopic Real Gases
scale using bulk properties such as pressure, density, volume, and temper-
ature. This chapter introduces the basic concepts employed in thermody-
namics including system, surroundings, intensive and extensive variables,
adiabatic and diathermal walls, equilibrium, temperature, and thermome-
try. The macroscopic variables pressure and temperature are also dis-
cussed in terms of a molecular level model. The usefulness of equations of
state, which relate the state variables of pressure, volume, and tempera-

ture, is also discussed for real and ideal gases.

What Is Thermodynamics and Why Is It
1.1 Useful?

Thermodynamics is the branch of science that describes the behavior of matter and the
transformation between different forms of energy on a macroscopic scale, or the human
scale and larger. Thermodynamics describes a system of interest in terms of its bulk prop-
erties. Only a few such variables are needed to describe the system, and the variables are
generally directly accessible through measurements. A thermodynamic description of
matter does not make reference to its structure and behavior at the microscopic level. For
example, 1 mol of gaseous water at a sufficiently low density is completely described by
two of the three macroscopic variables of pressure, volume, and temperature. By con-
trast, the microscopic scale refers to dimensions on the order of the size of molecules. At
the microscopic level, water would be described as a dipolar triatomic molecule, H O ,
2
with a bond angle of 104.5° that forms a network of hydrogen bonds.
In this book, we first discuss thermodynamics and then statistical thermodynamics.
Statistical thermodynamics (Chapters 31 and 32) uses atomic and molecular properties
to calculate the macroscopic properties of matter. For example, statistical thermody-
namics can show that liquid water is the stable form of aggregation at a pressure of
1 bar and a temperature of 90°C, whereas gaseous water is the stable form at 1 bar and
110°C. Using statistical thermodynamics, the macroscopic properties of matter are cal-
culated from underlying molecular properties.

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