Thermodynamic change

A thermodynamic change can take place in two ways - either reversibly, or irreversibly. In a reversible change, all the processes take place as efficiently as the second law of thermodynamics will allow them to. In this case the second law tells us that... 

Air treatment, thermodynamic Relating to the various thermodynamic changes that occur in the specific volume, enthalpy, and wet and dry bulb temperatures of treated air. 

A concept of the cycle of thermodynamic processes, introduced later than the Carnot cycle. Modifications of the Rankine cycle are of practical importance in boiler design, in relating the successive thermodynamic changes as water is converted to steam, expands and converted to mechanical energy in a turbine, then condenses and returns to the boiler. 

The molecular models of rubber elasticity relate chain statistics and chain deformation to the deformation of the macroscopic material. The thermodynamic changes, including stress are derived from chain deformation. In this sense, the measurement of geometric changes is fundamental to the theory, constitutes a direct check of the model, and is an unambiguous measure of the mutual consistency of theory and experiment. 

When the energetics of the ion-radical pair are taken as a close approximation to the transition state, the thermodynamic change can be reformulated in terms of relative reactivities, i.e.,... 

In previous chapters we looked at the way heat travels from hot to cold, as described by the so called minus-oneth law of thermodynamics, and the way net movements of heat cease at thermal equilibrium (as described by the zeroth law). Although this transfer of heat energy was quantified within the context of the first law, we have not so far been able to describe why such chemical systems occur. Thermodynamic changes only ever proceed spontaneously in one direction, but not the other. Why the difference ... 

As no chemical reactions occur, we note how these thermodynamic changes are purely physical. But since no bonds form or break, what is the impetus - the cause - of the transfer of energy ... 

We call the sum of the system and its surroundings the thermodynamic universe (see Figure 4.3). A thermodynamic universe is described as that volume large enough to enclose all the thermodynamic changes . The entropy change of the thermodynamic universe during crystallization is A (totai), which equates to... 

Any finite expansion that occurs in a finite time is irreversible. A reversible expansion can be approximated as closely as desired, and the values of the thermodynamic changes can be calculated for the limiting case of a reversible process. In the limiting case, the process must be carried out infinitely slowly so that the pressure P is always a well-defined quantity. A reversible process is a succession of states, each of which is an equilibrium state, in which the temperature and pressure have well-defined values such a process is also called a quasi-static process. 

The thermodynamic changes for reversible, free, and intermediate expansions are compared in the first column of Table 5.1. This table emphasizes the difference between an exact differential and an inexact differential. Thus, U and H, which are state functions whose differentials are exact, undergo the same change in each of the three different paths used for the transformation. They are thermodynamic properties. However, the work and heat quantities depend on the particular path chosen, even though the initial and final values of the temperature, pressure, and volume, respectively, are the same in all these cases. Thus, heat and work are not thermodynamic properties rather, they are energies in transfer between system and surroundings. 

So far we have not specified whether the adiabatic expansion under consideration is reversible. Equations (5.40), (5.42), and (5.44) for the calculation of the thermodynamic changes in this process apply to the reversible expansion, the free expansion, or the intermediate expansion, so long as we are dealing with an ideal gas. However, the niunerical values of W, AU, and AH will not be the same for each of the three types of adiabatic expansion because T2, the final temperature of the gas, will depend on the type of expansion, even though the initial temperature is identical in aU cases. 

TABLE 5.2. Thermodynamic Changes in Adiabatic Expansions of an Ideal Gas... 

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