CHAPTER 1
1 Introduction
Thermodynamics is a quantitative subject. It allows us to derive relations between the
values of numerous physical quantities. Some physical quantities, such as a mole fraction,
are dimensionless; the value of one of these quantities is a pure number. Most quantities,
however, are not dimensionless and their values must include one or moreunits. This
chapter reviews the SI system of units, which are the preferred units in science applications.
The chapter then discusses some useful mathematical manipulations of physical quantities
using quantity calculus, and certain general aspects of dimensional analysis.
1.1 Units
There is international agreement that the units used for physical quantities in science and
technology should be those of the International System of Units, or SI (standing for the
FrenchSysteme International d’Unit` ́es). The Physical Chemistry Division of the Inter-
national Union of Pure and Applied Chemistry, or IUPAC, produces a manual of recom-
mended symbols and terminology for physical quantities and units based on the SI. The
manual has become known as the Green Book (from the color of its cover) and is referred
to here as the IUPAC Green Book. This book will, with a few exceptions, use symbols rec-
ommended in the third edition (2007) of the IUPAC Green Book;^1 these symbols are listed
for convenient reference in AppendicesCandD.
The SI is built on the sevenbase unitslisted in Table1.1on the next page. These base
units are independent physical quantities that are sufficient to describe all other physical
quantities. One of the seven quantities, luminous intensity, is not used in this book and is
usually not needed in thermodynamics. The official definitions of the base units are given
in AppendixA.
Table1.2lists derived units for some additional physical quantities used in thermody-
namics. The derived units have exact definitions in terms of SI base units, as given in the
last column of the table.
The units listed in Table1.3are sometimes used in thermodynamics but are not part
of the SI. They do, however, have exact definitions in terms of SI units and so offer no
problems of numerical conversion to or from SI units.
(^1) Ref. [ 36 ]. The references are listed in the Bibliography at the back of the book.