In this chapter, the fundamental properties of matter are defined. Before
considering complex biological systems, a very simple system, called an ideal
or perfect gas, is described. This system is chosen as its properties can be
understood without any prior knowledge of its chemical or physical nature.
After the basic concepts are established, then we will go back and discuss
how certain physical properties, such as the size or charge of an object, can
be incorporated. The objective of this text is to focus thermodynamic con-
cepts on biological problems. Therefore, included at the end of the chapter
is a short review of the basic properties of biological systems, including
the structural properties of proteins and nucleic acids.
Fundamental thermodynamic concepts
States of matter
Matter can be considered to be in one of three states, a gas, liquid, or
solid. A gas is considered to be a fluid that always fills the container
that it occupies. The particles that form the gas are widely separated and
move in a disordered motion. A liquid is a fluid that, in the presence of
a gravitational field, occupies only the lower portion of a container and
has well-defined surfaces. The particles interact with each other weakly
at short distances, and the movement of any given particle is restricted
by collisions with other particles. A solid has a shape that is independent
of a container. The position of each particle is fixed although the particles
can vibrate about their position. From a thermodynamic viewpoint, the
basic difference between these three states is the difference in motion of
the particles, so transitions can be made between these states if the degree
of motion changes. These states are characterized by a few fundamental
properties, as described below.
Pressure
Pressure conceptually is a measure of the force that an object exerts on
the surface of another object. Formally, the pressure, P, is the force, F,
divided by the area, A:
(1.1)
A balloon expands due to the increase in pressure as air is forced inside
the balloon. The increase in the amount of air inside pushes on the walls
of the balloon making the pressure inside the balloon greater than the
pressure outside. The balloon expands until an equilibrium is reached, with
the pressures balanced, as will be discussed later.
P
F
A
==
Force
Area
1 Basic thermodynamic and biochemical concepts Preface xv
