Measured Thermodynamic Properties

By this time, you are probably experienced in working with units. Most science and engineering texts have a section in the first chapter on this topic. In this text, we will mainly use the Systeme International, or SI units. The SI unit system uses the primary dimensions m, s, kg, mol, and K. Details of different unit systems can be found in Appendix D. One of the easiest ways to tell that an equation is wrong is that the units on one side do not match the units on the other side. Probably the most common errors in solving problems result from dimensional inconsistencies. The upshot is Pay close attention to units Try not to write a number down without the associated units. You should be able to convert between unit systems. It is often easiest to put all variables into the same unit system before solving a problem. 

How many different units can you think of for length For pressure For energy  

We have seen that if we specify the property values of the substance(s) in a system, we define its thermodynamic state. It is typically the measured thermodynamic properties that form our gateway into characterizing the particular state of a system. Measured thermodynamic properties are those that we obtain through direct measurement in the lab. These include volume, temperature, and pressure. 

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Presents a variety of measured thermodynamic properties of binary mixtures these properties are often represented by empirical equations. 

Thermodynamic variables are related through a number of different thermodynamic equations. Experimentalists who measure thermodynamic properties by one method often check the results using other relationships. This test checks for thermodynamic consistency, which must follow if the results are to be trusted. 

The perturbation of the surface is automatically included in any measured thermodynamic property. In the presence of such a perturbation the thermodynamic properties of the adsorbed gas alone have no direct physical meaning, although the experimentally measured quantities are still well defined. 

Determination of transformation enthalpies in binary systems. Just as consistent values of for elements can be obtained by back-extrapolation from binary systems, so it is possible to obtain values of by extrapolating the enthalpy of mixing vs composition in an alloy system where the phase has a reasonable range of existence. The archetypal use of this technique was the derivation of the lattice stability of f.c.c. Cr from the measured thermodynamic properties of the Ni-based f c.c. solid solution (7) in the Ni-Cr system (Kaufman 1972). If it is assumed that the f.c.c. phase is a regular solution, the following expression can be obtained ... 

The cohesive energy of a metal (and the related measurable thermodynamic properties) is relatively easy to understand in a simplified picture of the metallic bond. 

As the temperature of a mixed surfactant system is increased above its cloud point, the coacervate (concentrated) phase may go from a concentrated micellar solution mixed ionic/nonionic systems, it would be of interest to measure thermodynamic properties of mixing in this coacervate as this temperature increased to see if the changes from micelle to concentrated coacervate were continuous or if discontinuities occurred at certain temperatures/compositions. The similarities and differences between the micelle and coacervate could be made clearer by such an experiment. 

TABLE 11.2 Measured Thermodynamic Properties (in SI Units) of Some Common Fluids at 20° C, 1 atm Molar Heat Capacity CP, Isothermal Compressibility jS7, Coefficient of Thermal Expansion otp, and Molar Volume V, with Monatomic Ideal Gas Values (cf. Sidebar 11.3) Shown for Comparison... 

Thermodynamic properties of imidazolium-based ionic liquids, such as densities, heat capacities, and enthalpies of fusion of [bmim] [PFg] and [bmim] [NTf2] have been determined and a critical analysis of the effect of impurities on the measured thermodynamic properties has been carried out <2006CED1856>. 

Enthalpy is the first of three thermodynamic properties that you will encounter in this chapter. Thermodynamics is a science that examines various processes and the energy changes that accompany the processes. By studying and measuring thermodynamic properties, chemists have learned to predict whether a chemical reaction can occur and what kind of energy change it will have. 

Calorimetry is the basic experimental method employed in thermochemistry and thermal physics which enables the measurement of the difference in the energy U or enthalpy of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or A//) is called a calorimeter. In the first section the relationships between the thermodynamic functions and calorimetry are established. The second section gives a general classification of calorimeters in terms of the principle of operation. The third section describes selected calorimeters used to measure thermodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

Measuring Thermodynamic Properties of Ions from Half-Cell Potentials... 

The assembly of the fundamental equations (5.39) to (5.42) together with (5.67) to (5.70) and (5.71) to (5.74) defines the thermodynamic network. These relations are the starting point for finding generalised computational methods for non-measurable thermodynamic properties from other measurable properties. 

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