Classical thermodynamics was developed during the nineteenth century
and remains a cornerstone for understanding the properties of matter.
This chapter presents the first law of thermodynamics, the conservation
of energy. The law may seem to be intuitive, as we know that a reaction
cannot produce more energy than was initially present and that hot objects
will always cool off due to loss of energy. However, the concept was not
always accepted as for many years people sought means to create energy
from nothing or from perpetual-energy machines. The failure of such efforts
coupled with the development of thermodynamics led to the concept that
energy cannot be created or destroyed but only converted from one form
to another. The conversion and storage of energy plays a critical role in
biological organisms. In mammals, energy is used to contract muscles and
released as work is performed in the form of walking or other motions.
In all organisms, energy is required to create and transport nutrients
and other cellular components such as proteins. The ability to perform
such processes is determined by the energy of the reaction, with many
key biological pathways making use of energy-rich compounds, such as
adenosine triphosphate, ATP, to drive a reaction. An understanding of these
fundamental biological processes requires knowledge of the basic concepts
of thermodynamics. The focus of this chapter is the introduction of the
terminology used to define the concepts followed by a description of the
different forms of energy, such as heat and enthalpy, and how these terms
are related in a thermodynamic setting.
Systems
Energy can readily flow between objects; for example, if an ice cube is
placed into a cup of warm water, the ice cube is heated up and melted
by the water. While the energy of the ice cube increases during this pro-
cess, the conservation of energy requires that the temperature of the water