Page 26 - Bruno Linder Elementary Physical Chemistry

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

Chapter 2

The First Law of Thermodynamics

Thermodynamics is concerned with the laws that govern the transformation
of one kind of energy into another during a physical or chemical change.
The term energy is difficult to define rigorously. An intuitive way is
to say that energy is the capacity to do work.
There are various classifications of energy, all having the dimension (in
2 −2
SI units) of kg m s .

2.1. Classification
If N A is Avogadro’s number, then Nm = nN A m = nM,where M is the
molar mass. Thus,
1 2
PV = nM c
3

Equating this to the ideal gas law gives, for n =1,
2
c = 3RT/M

A. Kinetic and Potential Energy. Kinetic energy is the energy an object
possesses by virtue of its motion. Potential energy is the energy an object
possesses by virtue of its position or composition. This classification is not
very useful in Thermodynamics.
B. In Thermodynamics the most useful forms of energy are Work, Heat,
Internal Energy, and related forms, such as Enthalpy, Free Energy, etc. to
be introduced later.

11