Chap06 soln

Physical Chemistry

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
6 Physical transformations of pure substances Solutions to exercises Discussion questions E6.1(b) Refer to Fig. 6.8. The white lines represent the regions of superheating and supercooling. The chemical potentials along these lines are higher than the chemical potentials of the stable phases represented by the colored lines. Though thermodynamically unstable, these so-called metastable phases may persist for a long time if the system remains undisturbed, but will eventually transform into the thermo- dynamically stable phase having the lower chemical potential. Transformation to the condensed phases usually requires nucleation centers. In the absence of such centers, the metastable regions are said to be kinetically stable. E6.2(b) At 298 K and 1.0 atm, the sample of carbon dioxide is a gas. (a) After heating to 320 K at constant pressure, the system is still gaseous. (b) Isothermal compression at 320 K to 100 atm pressure brings the sample into the supercritical region. The sample is now not much different in appearance from ordinary carbon dioxide, but some of its properties are (see Box 6.1). (c) After cooling the sample to 210 K at constant pressure, the carbon dioxide sample solidi±es. (d) Upon reducing the pressure to 1.0 atm at 210 K, the sample vapourizes (sublimes); and ±nally (e) upon heating to 298 K at 1.0 atm, the system has resumed its initial conditions in the gaseous state. Note the lack of a sharp gas to liquid transition in steps (b) and (c). This process illustrates the continuity of the gaseous and liquid states. E6.3(b) First-order phase transitions show discontinuities in the ±rst derivative of the Gibbs energy with respect to temperature. They are recognized by ±nite discontinuities in plots of H , U , S , and V against temperature and by an in±nite discontinuity in C p . Second-order phase transitions show discontinuities in the second derivatives of the Gibbs energy with respect to temperature, but the ±rst derivatives are continuous. The second-order transitions are recognized by kinks in plots of H , U , S , and V against temperature, but most easily by a ±nite discontinuity in a plot of C p against temperature. A λ -transition shows characteristics of both ±rst and second-order transitions and, hence, is dif±cult to classify by the Ehrenfest scheme. It resembles a ±rst-order transition in a plot of C p against T ,but appears to be a higher-order transition with respect to other properties. See the book by H. E. Stanley listed under Further reading for more details. Numerical exercises E6.4(b) Assume vapour is a perfect gas and 1 vap H is independent of temperature ln p p =+ 1 vap H R ± 1 T 1 T ² 1 T = 1 T + R 1 vap H ln p p = 1 293 . 2K + 8 . 314 J K 1 mol 1 32 . 7 × 10 3 J mol 1 × ln ± 58 . 0 66 . 0 ² = 3 . 378 × 10 3 K 1 T = 1 3 . 37 8 × 10 3 K 1 = 296 K = 23 C
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
88 INSTRUCTOR S MANUAL E6.5(b) d p d T = 1S m 1V m 1 fus S = 1V m ± d p d T ² 1V m 1p 1T assuming 1 fus S and 1V m independent of temperature.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 01/29/2008.

Page1 / 10

Chap06 soln - 6 Physical transformations of pure substances...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online