Page 25 - Thermodynamics of Biochemical Reactions

Thernwdyanamics of Biochemical Reactions. Robert A. Alberty
Copyright 0 2003 John Wiley & Sons, Inc.
ISBN 0-471-22851-6

rn 2.1 State of a System
rn 2.2 Fundamental Equation for the Internal Energy
rn 2.3 Maxwell Equations
rn 2.4 Gibbs-Duhem Equation and the Phase Rule
rn 2.5 Legendre Transforms for the Definition of
Additional Thermodynamic Potentials
rn 2.6 Thermodynamic Potentials for a Single-Phase
System with One Species
rn 2.7 Other Kinds of Work
rn 2.8 Calculation of Thermodynamic Properties of a
Monatomic Ideal Gas from Derivatives of a
Thermodynamic Potential

According to the first law of thermodinamics, there is a thermodynamic property
U of a system, called the internal energy. The change in internal energy in a
change in the state of a system is given by AU = q + w, where q is the heat flow
into the system and w is the work done on the system. The work can be
pressure-volume work, work of transport of electric charge, chemical work (more
on this later), work of stretching an elastomer, and so on.
The second law of thermodynamics has two parts. According to the first part
there is a thermodynamic property S of a system, called the entropy. The change
in entropy in a reversible change from one state of a system to another is given
by AS = 417; where T is the absolute temperature. According to the second part
of the second law, when a change takes place spontaneously in an isolated system,
AS is greater than zero. This is a remarkable result because it provides a way to
calculate whether a specified change in state can take place in a system on the
basis of other types of measurements on the system. These conclusions apply to
systems consisting of phases that are uniform in composition and do not have
gradients of temperature or concentration in them.
These two laws can be combined for a system involving only pressure-volume
work to obtain dU = TdS - PdV This so-called fundamental equation shows two
things: (1) thermodynamic properties of a system obey the rules of calculus and
(2) the choice of independent variables (in this case S and V) plays a very
important role in thermodynamics. The second law can be used to show that
when S and I/ are held constant, the internal energy U of a system must decrease

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