Page 40 - Physical chemistry eng

2 CHAPTER

Heat, Work, Internal 2.1 The Internal Energy and the
First Law of Thermodynamics
Energy, Enthalpy, and 2.2 Work
2.3
Heat
2.4 Doing Work on the System
the First Law of and Changing the System
Energy from a Molecular
Level Perspective
Thermodynamics 2.5 Heat Capacity

2.6
State Functions and Path
Functions
2.7 Equilibrium, Change, and
Reversibility
In this chapter, the internal energy U is introduced. The first law of ther-
2.8 Comparing Work for
modynamics relates ¢U to the heat (q) and work (w) that flows across the Reversible and Irreversible
Processes
boundary between the system and the surroundings. Other important
2.9 Determining ¢U and
concepts introduced include heat capacity, the difference between state Introducing Enthalpy, a New
and path functions, and reversible versus irreversible processes. The State Function
2.10 Calculating q, w, ¢U , and
enthalpy H is introduced as a form of energy that can be directly meas-
¢H for Processes Involving
ured by the heat flow in a constant pressure process. We show how ¢U , Ideal Gases
¢H , q, and w can be calculated for processes involving ideal gases. 2.11 The Reversible Adiabatic
Expansion and Compression
of an Ideal Gas

The Internal Energy and the First Law of
2.1 Thermodynamics

This section focuses on the change in energy of the system and surroundings during a
thermodynamic process such as an expansion or compression of a gas. In thermo-
dynamics, we are interested in the internal energy of the system, as opposed to the
energy associated with the system relative to a particular frame of reference. For exam-
ple, a container of gas in an airplane has a kinetic energy relative to an observer on the
ground. However, the internal energy of the gas is defined relative to a coordinate sys-
tem fixed on the container. Viewed at a molecular level, the internal energy can take on
a number of forms such as
• the translational energy of the molecules.
• the potential energy of the constituents of the system; for example, a crystal consist-
ing of polarizable molecules will experience a change in its potential energy as an
electric field is applied to the system.
• the internal energy stored in the form of molecular vibrations and rotations.
• the internal energy stored in the form of chemical bonds that can be released
through a chemical reaction.
• the potential energy of interaction between molecules.
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