28.12.2013 Views

preface to fifteenth edition

preface to fifteenth edition

preface to fifteenth edition

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

6.4 THERMODYNAMICPROPERTIES<br />

in which a, b, and c are empirical constants. These constants may be evaluated by taking three pieces<br />

of data: (T 1 , C p,1 ), (T 2 , C p,2 ), and (T 3 , C p,1 ), and substituting in the following expressions:<br />

Cp,1 Cp,2 Cp,3<br />

c (6.14)<br />

(T1 T 2)(T1 T 3) (T2 T 1)(T2 T 3) (T3 T 2)(T3 T 1)<br />

Cp,1 Cp,2 [(T 1 T 2 )c] b<br />

T1 T2<br />

(6.15)<br />

2<br />

(Cp,1 bT 1) cT1<br />

a (6.16)<br />

Smoothed data presented at rounded temperatures, such as are available in Tables 6.2 and 6.4, plus<br />

the C p values at 298 K listed in Table 6.1 and 6.3, are especially suitable for substitution in the<br />

foregoing parabolic equations. The use of such a parabolic fit is appropriate for interpolation, but<br />

data extrapolated outside the original temperature range should not be sought.<br />

6.1.1.4Enthalpy of a System The enthalpy increment of a system over the interval of temperature<br />

from T 1 <strong>to</strong> T 2 , under the constraint of constant pressure, is given by the expression:<br />

<br />

T 2<br />

H H C dT (6.17)<br />

2 1 p<br />

T 1<br />

The enthalpy over a temperature range that includes phase transitions, melting, and vaporization, is<br />

represented by:<br />

T<br />

<br />

T<br />

<br />

T2 Tm<br />

H H C (c,II) dT Ht C (c,I) dT Hm<br />

2 1 p p<br />

1 1<br />

Tb T2<br />

C (1q) dT Hv C (g) dT (6.18)<br />

Integration of heat capacities, as expressed by Eq. (6.13), leads <strong>to</strong>:<br />

Tm<br />

6.1.1.5 Entropy In the physical change of state,<br />

is the entropy of melting (or fusion),<br />

is the entropy of vaporization, and<br />

is the entropy of sublimation.<br />

p<br />

Tb<br />

2 2 3 3<br />

b(T2 T 1) c(T2 T 1)<br />

H a(T2 T 1) (6.19)<br />

2 3<br />

p<br />

Hm<br />

Sm (6.20)<br />

T m<br />

Hv<br />

Sv (6.21)<br />

T b<br />

Hs<br />

Ss (6.22)<br />

Ts

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!