Page 27 - Bruno Linder Elementary Physical Chemistry

August 25, 2010 9:36 9in x 6in b985-ch02 Elementary Physical Chemistry

12 Elementary Physical Chemistry

2.2. System and Surrounding

We now introduce concepts which are essential to the application of
thermodynamics, namely

• system, which is part of the universe in which one is interested, and
• surrounding, the rest of the universe or what is not the system.
It is convenient to characterize a system as either

• Open, which is a system that can exchange energy and matter with the
surrounding, or
• Closed, which is a system that cannot exchange matter with surround-
ing, or
• Isolated, which is a system that cannot exchange energy or matter with
the surrounding.

2.3. Work and Heat
Work and Heat are always associated with transfer of energy between
systems and surrounding. More explicitly, Work is the energy transfer
˙
that can be used to move boundaries of a system, or lift weight. Heat is
the energy transfer due to temperature difference between the system and
surrounding. Energy is a property of the system.

Comment: There are various types of work: work associated with
expansion or compression (we will call that PV work), electrical work,
gravitational and other types of work. We will denote the pressure–
volume work as w PV and all types of work as w other . For the most
part, we will be concerned in this course with PV work.

Temperature obviously plays an important role in thermodynamics. The
definition used here — thinking of temperature as a measure of degrees
of hotness or coolness — is obviously not rigorous. There is a rigorous
approach, the axiomatic approach, but it will not be pursued in this course.
From a molecular (as opposed to thermodynamic) point of view, work
is a form of energy transfer that utilizes uniform motion of the molecules
in the surrounding. Heat is energy transfer that involves chaotic motion
of the surrounding molecules.