Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Physical chemistry entropy

In physical chemistry, entropy has been introduced as a measure of disorder or lack of structure. For instance the entropy of a solid is lower than for a fluid, because the molecules are more ordered in a solid than in a fluid. In terms of probability it means also that in solids the probability distribution of finding a molecule at a given position is narrower than for fluids. This illustrates that entropy has to do with probability distributions and thus with uncertainty. One of the earliest definitions of entropy is the Shannon entropy which is equivalent to the definition of Shannon s uncertainty (see Chapter 18). By way of illustration we... [Pg.558]

The subject of entropy is introduced here to illustrate treatment of experimental data sets as distinct from continuous theoretical functions like Eq. (1-33). Thermodynamics and physical chemistry texts develop the equation... [Pg.24]

Thermodynamics is one of the most well-developed mathematical descriptions of chemistry. It is the held of thermodynamics that dehnes many of the concepts of energy, free energy and entropy. This is covered in physical chemistry text books. [Pg.9]

Remember that the hump which causes the instability with respect to phase separation arises from an unfavorable AH considerations of configurational entropy alone favor mixing. Since AS is multiplied by T in the evaluation of AGj, we anticipate that as the temperature increases, curves like that shown in Fig. 8.2b will gradually smooth out and eventually pass over to the form shown in Fig. 8.2a. The temperature at which the wiggles in the curve finally vanish will be a critical temperature for this particular phase separation. We shall presently turn to the Flory-Huggins theory for some mathematical descriptions of this critical point. The following example reminds us of a similar problem encountered elsewhere in physical chemistry. [Pg.530]

Qualitative and quantitative relations between enthalpy and entropy were observed several times in the 1920 s, and their importance was rightly recognized by some authors. However, some ideas from this early work seem to have been overlooked later, perhaps because they were connected with obsolete theories or because they were developed independently in the fields of organic chemistry, catalysis, and pure physical chemistry. For this reason, a brief historical survey seems appropriate. [Pg.417]

Nagoe, M. Morimoto, T. (1969). Differential heat of adsorption and entropy of water absorbed on zinc oxide surface. Journal of Physical Chemistry, 73, 3809-14. [Pg.355]

Natural phenomena are striking us every day by the time asymmetry of their evolution. Various examples of this time asymmetry exist in physics, chemistry, biology, and the other natural sciences. This asymmetry manifests itself in the dissipation of energy due to friction, viscosity, heat conductivity, or electric resistivity, as well as in diffusion and chemical reactions. The second law of thermodynamics has provided a formulation of their time asymmetry in terms of the increase of the entropy. The aforementioned irreversible processes are fundamental for biological systems which are maintained out of equilibrium by their metabolic activity. [Pg.84]

Figures 13.2,13.3,13.4, 13.5,13.6,13.11 and 13.12 are reproduced with permission from the Royal Society of Chemistry from Chemical Society Reviews, 31, Krishna, R., Smit, B., and Calero, S., Entropy effects during sorption of alkanes in zeolites, p. 185-194, Copyright The Royal Society of Chemistry (2002) http //www.rsc.org/Puhlishing/Joumals/ CS/article.asp doi=bl01267n Figures 13.7 and 13.8 are reprinted with permission from the Journal of Physical Chemistry B, 101 (8), Eder, E., Lercher, J.A., On the role of the pore size and tortuosity for sorption of alkanes in molecular sieves, p. 1273-1278,... Figures 13.2,13.3,13.4, 13.5,13.6,13.11 and 13.12 are reproduced with permission from the Royal Society of Chemistry from Chemical Society Reviews, 31, Krishna, R., Smit, B., and Calero, S., Entropy effects during sorption of alkanes in zeolites, p. 185-194, Copyright The Royal Society of Chemistry (2002) http //www.rsc.org/Puhlishing/Joumals/ CS/article.asp doi=bl01267n Figures 13.7 and 13.8 are reprinted with permission from the Journal of Physical Chemistry B, 101 (8), Eder, E., Lercher, J.A., On the role of the pore size and tortuosity for sorption of alkanes in molecular sieves, p. 1273-1278,...
Figure 10. LCT configurational entropy ScT as a function of the reduced temperature 5T = (T — To)/To for low and high molar mass F-F and F-S polymer fluids at constant pressure of P = 1 atm (0.101325 MPa). The product ScT is normalized by the thermal energy k To at the ideal glass transition temperature To- (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005 American Chemical Society.)... Figure 10. LCT configurational entropy ScT as a function of the reduced temperature 5T = (T — To)/To for low and high molar mass F-F and F-S polymer fluids at constant pressure of P = 1 atm (0.101325 MPa). The product ScT is normalized by the thermal energy k To at the ideal glass transition temperature To- (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005 American Chemical Society.)...
Figure 22. The configurational entropy Sc per lattice site as calculated from the LCT for a constant pressure, high molar mass (M = 40001) F-S polymer melt as a function of the reduced temperature ST = (T — To)/Tq, defined relative to the ideal glass transition temperature To at which Sc extrapolates to zero. The specific entropy is normalized by its maximum value i = Sc T = Ta), as in Fig. 6. Solid and dashed curves refer to pressures of F = 1 atm (0.101325 MPa) and P = 240 atm (24.3 MPa), respectively. The characteristic temperatures of glass formation, the ideal glass transition temperature To, the glass transition temperature Tg, the crossover temperature Tj, and the Arrhenius temperature Ta are indicated in the figure. The inset presents the LCT estimates for the size z = 1/of the CRR in the same system as a function of the reduced temperature 5Ta = T — TaI/Ta. Solid and dashed curves in the inset correspond to pressures of P = 1 atm (0.101325 MPa) and F = 240 atm (24.3 MPa), respectively. (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005, American Chemical Society.)... Figure 22. The configurational entropy Sc per lattice site as calculated from the LCT for a constant pressure, high molar mass (M = 40001) F-S polymer melt as a function of the reduced temperature ST = (T — To)/Tq, defined relative to the ideal glass transition temperature To at which Sc extrapolates to zero. The specific entropy is normalized by its maximum value i = Sc T = Ta), as in Fig. 6. Solid and dashed curves refer to pressures of F = 1 atm (0.101325 MPa) and P = 240 atm (24.3 MPa), respectively. The characteristic temperatures of glass formation, the ideal glass transition temperature To, the glass transition temperature Tg, the crossover temperature Tj, and the Arrhenius temperature Ta are indicated in the figure. The inset presents the LCT estimates for the size z = 1/of the CRR in the same system as a function of the reduced temperature 5Ta = T — TaI/Ta. Solid and dashed curves in the inset correspond to pressures of P = 1 atm (0.101325 MPa) and F = 240 atm (24.3 MPa), respectively. (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005, American Chemical Society.)...
Next, we review findings of educational research about the main areas of physical chemistry. Most of the work done was in the areas of basic thermodynamics and electrochemistry, and some work on quantum chemistry. Other areas, such as chemical kinetics, statistical thermodynamics, and spectroscopy, have not so far received attention (although the statistical interpretation of entropy is treated in studies on the concepts of thermodynamics). Because many of the basics of physical chemistry are included in first-year general and inorganic courses (and some even in senior high school), many of the investigations have been carried out at these levels. [Pg.84]

Two papers reported powder pattern crystallographic results. The paper by Santos et al. (7) stood out from the rest because it presented a collection of more classical physical chemistry experiments. In this paper the authors described the use of micro-combustion calorimetry, Knudsen effusion to determine enthalpy of sublimation, differential scanning calorimetry, X-ray diffraction, and computed entropies. While this paper may provide some justification for including bomb calorimetry and Knudsen cell experiments in student laboratories, the use of differential scanning calorimetry and x-ray diffraction also are alternatives that would make for a crowded curriculum. Thus, how can we choose content for the first physical chemistiy course that shows the currency of the discipline while maintaining the goal to teach the fundamentals and standard techniques as well ... [Pg.178]

More detailed discussion of enthalpy, free energy, and entropy are given in books on thermodynamics, and the relationships between these quantities and processes at the molecular level are explained in books on statistical mechanics [140] general discussions of these topics are given in physical chemistry texts. [Pg.298]

As previously, the sources on statistical thermodynamics are hardly numerable. Conciseness in them struggles with comprehensibility and both lose. Elementary information is given in physical chemistry courses already mentioned [1,2]. More fundamental courses are [3] - a rather physical one and [4] - a classical text on this subject. An interesting approach based on consistent usage of a single quantity - the entropy - is described in [5]. [Pg.4]

Furthermore, you will need to have a working knowledge of entropy and free energy, as these are quantities that are essential prerequisites for the proper understanding of the physics and physical chemistry of polymers (or any other material, for that matter). [Pg.282]

Radiotracer methods are the methods of choice for investigation of reaction mechanisms. They have also found broad application for determination of kinetic data of chemical reactions such as reaction rates, activation energies and entropies. Only a few examples can be given of the multitude of applications in organic, inorganic and physical chemistry and in biochemistry. [Pg.359]

Frank, H. S., Evans, M. W. (1945). Free volume and entropy in condensed systems. Journal of Chemical Physics, 13, 507-532. Gill, S. J., Dec, S. F., Olofsson, G., Wadso, I. (1985). Anomalous heat capacity of hydrophobic solvation. Journal of Physical Chemistry, 89, 3758-3761. [Pg.33]

Vesnaver, G., Kranjc, Z., Pohar, C., and Skerjanc, J. Free enthalpies, enthalpies, and entropies of dilution of aqueous-solutions of alkaline-earth poly(styrenesulfonates) at different temperatures. Journal of Physical Chemistry, 1987, 91, No. 14, p. 3845-3848. [Pg.225]

S = Clausius entropy) requires further explanation, into which we shall enter in Chapter VI in general, the application of equation (1) is quite simple and straightforward, particularly in physical chemistry, and it is done so frequently in recent literature that it may here be taken for granted. [Pg.3]

Larionov and co-workers (Institute of Physical Chemistry, the U.S.S.R. Academy of Sciences, Moscow) (308-312) carried out systematic theoretical and experimental investigations of the adsorption from liquid solutions of nonelectrolytes on silica adsorbents. They studied the adsorption of individual substances and binary liquid solutions (benzene/carbon tetrachloride, carbon tetrachloride/isooctane, benzene/isooctane, etc.) on Si02 samples with different degrees of porosity but identical surface chemical properties. The experimental results were compared with the theoretical calculations carried out by the Gibbs method. This procedure made it possible to calculate the dependence of the enthalpy, entropy, and free energy of wetting on the concentration and to obtain expressions describ-... [Pg.626]


See other pages where Physical chemistry entropy is mentioned: [Pg.842]    [Pg.422]    [Pg.119]    [Pg.261]    [Pg.463]    [Pg.654]    [Pg.20]    [Pg.18]    [Pg.19]    [Pg.23]    [Pg.85]    [Pg.181]    [Pg.286]    [Pg.288]    [Pg.178]    [Pg.2]    [Pg.272]    [Pg.7]    [Pg.5]    [Pg.3]    [Pg.151]    [Pg.7]    [Pg.178]    [Pg.53]    [Pg.265]    [Pg.412]    [Pg.449]    [Pg.91]    [Pg.158]   
See also in sourсe #XX -- [ Pg.138 ]




SEARCH



Chemistry physical

Physical chemistry physics

© 2024 chempedia.info