Conversion processes work, reversible

Since is defined as work done on the system, the minimum amount of work necessary to produce a given change in the system is that in a reversible process. Conversely, the amount of work done by the system on the surroundings is maximal when the process is reversible. 

Heat, like work, is energy in transit and is not a function of the state of a system. Heat and work are interconvertible. A steam engine is an example of a machine designed to convert heat into work.h The turning of a paddle wheel in a tank of water to produce heat from friction represents the reverse process, the conversion of work into heat. 

All the expressions for % — evidently represent the dissipation of energy which occurs when the gases are allowed to mix by diffusion in the specified manner. It follows from the principle of dissipation of energy that work will have to be spent in separating the mixture into its constituents, and, conversely, work should be obtained if the gases are allowed to mix in a suitable manner. The first quantity of work will be a minimum, the latter a maximum, and both equal and opposite, when the processes are conducted reversibly. 

The reversible process (for which the equal sign applies) gives the maximum efficiency for the conversion of heat into work, but even the reversible engine is limited in the extent to which heat can be converted into work. 

Thus, in a reversible process that is both isothermal and isobaric, dG equals the work other than pressure-volume work that occurs in the process." Equation (3.96) is important in chemistry, since chemical processes such as chemical reactions or phase changes, occur at constant temperature and constant pressure. Equation (3.96) enables one to calculate work, other than pressure-volume work, for these processes. Conversely, it provides a method for incorporating the variables used to calculate these forms of work into the thermodynamic equations. 

It should be noted that r y is the maximum thermodynamic efficiency obtained under reversible conditions, i.e., such that the rate of any photochemical reaction from D is infinitesimally slow. Although riy has some theoretical interest, it has no practical interest since we are interested in maximizing the rate of a photochemical reaction from D which will lead to the production of useful work. The rate of energy conversion by such a process can be defined as... 

We have already inferred several methods by which a transition from etching to polymerization might be accomplished. These involved the effective lowering of the F/C ratio in the system by, for example, the addition of Hj or C2F to a CF, plasma or even the effective removal of fluorine by conversion to stable volatile fluorides in the etching process. The transition in the reverse direction (from polymerization to etching) may also be achieved by, for example, for example, the addition of Oj to a CjF plasma to effectively remove carbon as CO. In much of the work to be discussed below, CjFg is employed in the system whose F/C stoichiometry allows convenient rates of both etching and polymerization to be maintained. 

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