Thermodynamics and Chemistry

CHAPTER 2 SYSTEMS AND THEIR PROPERTIES

2.3 SOMEBASICPROPERTIES ANDTHEIRMEASUREMENT 36

0 200 400 600

0

0:2

0:4

0:6

0:8

1:0

1:2

p/bar

. Z

710 K

400 K

310 K

(a)

200 400 600 800 1000

 250

 200

 150

 100

 50

0

50

T/K

B

/cm

3

mol

^1

(b)

Figure 2.3 (a) Compression factor of CO 2 as a function of pressure at three temper-

atures. At 710 K, the Boyle temperature, the initial slope is zero.

(b) Second virial coefficient of CO 2 as a function of temperature.

2.2.6 Solids

A solid phase responds to a small applied stress by undergoing a smallelastic deformation.
When the stress is removed, the solid returns to its initial shape and the properties return to
those of the unstressed solid. Under these conditions of small stress, the solid has an equa-
tion of state just as a fluid does, in whichpis the pressure of a fluid surrounding the solid
(the hydrostatic pressure) as explained in Sec.2.3.4. The stress is an additional independent
variable. For example, the length of a metal spring that is elastically deformed is a unique
function of the temperature, the pressure of the surrounding air, and the stretching force.
If, however, the stress applied to the solid exceeds its elastic limit, the response isplastic
deformation. This deformation persists when the stress is removed, and the unstressed solid
no longer has its original properties. Plastic deformation is a kind of hysteresis, and is
caused by such microscopic behavior as the slipping of crystal planes past one another in a
crystal subjected to shear stress, and conformational rearrangements about single bonds in
a stretched macromolecular fiber. Properties of a solid under plastic deformation depend on
its past history and are not unique functions of a set of independent variables; an equation
of state does not exist.

2.3 Some Basic Properties and Their Measurement

This section macroscopic discusses aspects of the macroscopic properties mass, volume,
density, pressure, and temperature, with examples of how these properties can be measured.

2.3.1 Mass

We may measure the mass of an object with a balance utilizing the downward force ex-
erted on the object by the earth’s gravitational field. The classic balance has a beam and
knife-edge arrangement to compare the gravitational force on the body of interest with the