Energy reversible process, general case

Since it is relatively easy to transfer molecules from bulk liquid to the surface (e.g. shake or break up a droplet of water), the work done in this process can be measured and hence we can obtain the value of the surface energy of the liquid. This is, however, obviously not the case for solids (see later section). The diverse methods for measuring surface and interfacial energies of liquids generally depend on measuring either the pressure difference across a curved interface or the equilibrium (reversible) force required to extend the area of a surface, as above. The former method uses a fundamental equation for the pressure generated across any curved interface, namely the Laplace equation, which is derived in the following section. 

This criterion is good for establishish whether a process is under thermodynamic control. Care should be taken however to understand the term reversibility in this case. The folding of a protein is generally per se a chemically irreversible process, in the sense that the chemical equilibrium is overwhelmingly shifted towards the folded form - there is not a low activation energy barrier between the native folded and the unfolded form and a corresponding chemical equilibrium in the native state between the two forms. Thus, in the case of the thermodynamic hypothesis of... 

A typical set of the required five variables would be the temperatures and pressures of the inlet and outlet water streams, T, Tg, P, and Pg, plus the inlet water flow rate N. With values for these five variables, we can solve the steady-state material balance for the outlet water flow rate (the inlet and outlet mass flow rates are equal here) and we can solve the steady-state energy balance for Q. In this example the value computed for the heat duty is the actual value for the real process, regardless of reversibility, because the process is workfree. However, in the general case, when heat and work both cross a system boundary, the energy balance gives only their sum. Variations on this problem are also possible for example, if we knew values for the five variables T, Tg, P, Pg and Q, then we could solve the energy balance for the required water flow rate. Or, if we knew T, P, P , Q, and N, then we could solve for the outlet water temperature Tg. 

Many association reactions, as well as their reverse unimolecular decompositions, exhibit rate parameters that depend both on temperature and pressure, i.e., density, at process conditions. This is particularly the case for molecules with fewer than 10 atoms, because these small species do not have enough vibrational and rotational degrees of freedom to retain the energy imparted to or liberated within the species. Under these conditions, energy transfer rates affect product distributions. Consequently, the treatment of association reactions, in general, would be different than that of the fission reactions. 

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