Maximum work function

Table 9.2 Dipole moment, maximum work function change and charge transfer for potassium adsorbed on transition metal surfaces.

Fig. 4. Sustained oscillations that occur during the oxidation of CO over Pt(lOO) at 500 K, Poj = 5 X 10 Pa, Pco = 5 X lo Pa. The dashed vertical lines that coincide with the sudden decrease in the c(2 X 2) signal occur at the maximum work function (oxygen coverage), which also corresponds to the maximum production rate of CO2. The next vertical line corresponds to the maximum in the hex signal, and the simultaneous minima for the oxygen surface coverage and the CO2 production rate (after 82).

In the past, A has been known by a number of names work function, maximum work function, Helmholtz function, Helmholtz free energy, and simply free energy. The lUPAC agreement is to use the symbol A and call it the Helmholtz energy. 

Table 1. Summary of experimental results for halogen adsorption on (100) surfaces of fee transition metals. The "coverage" refers to the maximum coverage obtained for the corresponding adsorbate stmcture. The initial sticking coefficient is denoted by So, the temperature programmed desorption (TPD) peak temperature Tp, and the maximum work function change by A( ). For surfaces where more than one adsorbate structure is observed, the desorption peak temperature refers to new desorption features observed when the stmcture changes. ...

The free energy at constant volume is called the Helmoltz free energy (A.4) or maximum work function and is given by Equation (3). It is the difference between the free energies of products and reactants when a reaction occurs in a closed vessel. There is no change in volume, so no work is done against an applied pressure. 

Based on the d-interionic bonding theory [78], the maximum work function, chemical potential, exchange current density, and catalytic activity can be achieved by optimal inter-metallic d-electronic configuration between transition elements. The transfer of anti-bonding... 

Values of the average work function (<(), electronvolts) for the commonly used filament metals. The melting points of the metals are also shown to give some guidance as to the maximum temperature at which they can be used. Normally, the practical maximum would lie a few hundred degrees below the melting point to prevent sagging of the filament. 

Photoemission - Electromagnetic radiation of energy can cause photoemission of electrons whose maximum energy is equal to or larger than the difference between the photon energy and the work function of the material. 

Here Bq is the steady flow availability function at the so-called dead state, where the fluid is in equilibrium with the environment, at state (po> T )- The maximum work obtainable between states X and Y may then be written as... 

Work function or maximum work (Helmholtz free energy)... 

Other thermodynamic functions described above in that the change in free energy AG is determined solely by the initial and final states of the system. The maximum work, or maximum available energy, defined in terms of the Gibbs free energy G, which is now called the free enthalpy, is... 

Figure 8.23. Effect of catalyst potential and work function on the rate of CH4 oxidation to C02 on Pt for a low (1 1) CH4 to 02 feed ratio. Maximum methane conversion is 4%. pCH4= Po2as2 kPa, T, °C, r0, mol O/s.29 Reprinted with permission from Academic Press.

If the work function is smaller than the ionization potential of metastable state (see. Fig. 5.18b), then the process of resonance ionization becomes impossible and the major way of de-excitation is a direct Auger-deactivation process similar to the Penning Effect ionization a valence electron of metal moves to an unoccupied orbital of the atom ground state, and the excited electron from a higher orbital of the atom is ejected into the gaseous phase. The energy spectrum of secondary electrons is characterized by a marked maximum corresponding to the... 

The work function for barium is 2.48 eV. If light having a wavelength of 400 nm is shone upon a barium cathode, what is the maximum velocity of the ejected electrons ... 

The energy relations associated with the redox processes in wastewater follow the general rules of thermodynamics (Castellan, 1975 Atkins, 1978). The Gibbs free energy, G, of the system is the major thermodynamic function defining the state — and the change in state — of the biochemical redox processes. At constant temperature and under constant pressure, AG is equal to the maximum work, which can be produced by the redox process ... 

In our exposition of the properties of the Gibbs function G (Chapter 7), we examined systems with constraints on them in addition to the ambient pressure. We found that changes in Gibbs function are related to the maximum work obtainable from an isothermal transformation. In particular, for a reversible transformation at constant pressure and temperature [Equation (7.79)],... 

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