Activation energy,-decreasing

Relationships between reaction rate and temperature can thus be used to detect non-classical behaviour in enzymes. Non-classical values of the preexponential factor ratio (H D i 1) and difference in apparent activation energy (>5.4kJmoRi) have been the criteria used to demonstrate hydrogen tunnelling in the enzymes mentioned above. A major prediction from this static barrier (transition state theory-like) plot is that tunnelling becomes more prominent as the apparent activation energy decreases. This holds for the enzymes listed above, but the correlation breaks down for enzymes... 

The activation energy of this process increases in the Si-Ge-Sn series, except for the cases of X = NMe. On going from phosphorus to arsenic betaines, the activation energy decreases by 5-15 kcal/mol, and the stability of the reaction products increases similarly. 

Hydrogen transfer from the gas phase to the liquid phase becomes rate limiting with very fast hydrogenations (or with insufficient agitation). The observed reaction rate is then equal to the rate of gas-liquid mass transfer of hydrogen and becomes first order in hydrogen and independent of substrate concentration. The activation energy decreases to that of a diffusion process. 

The addition of an ionic conductive phase, such as GDC, also promotes the elec-trocatalytic activity of an MIEC cathode. Hwang et al. [108] studied the electrochemical activity of LSCF6428/GDC composites for the 02 reduction and found that the activation energy decreased from 142 kJmol-1 for the pure LSCF electrode to 122 kJmol1 for the LSCF/GDC composite electrodes. Thus, the promotion effect of the GDC is most effective at low-operation temperatures (Figure 3.12). This is due to the high ionic conductivity of the GDC phase at reduced temperatures. 

The principal advantage of catalysis is to make a reaction proceed more quickly because the activation energy decreases. 

In summary, when using an isotopic system to determine the age, the meaning of the age is the closure age, as defined in Figure 1-20. The temperature at the time of closure is referred to as the closure temperature (Tc), which varies from one mineral to another. Tc decreases as diffusivity in the mineral increases, or activation energy decreases, or grain size decreases. Tc of some isotopic systems (such as U-Pb in zircon) is high and the isotopic systems hence record an older age that... 

It can be seen that both the condnctivity and the activation energy decrease with increasing Sb content. 

In discussing doping of organic compounds allowance must be made for the fact that activation energy decreases with concentration of doping compound (see Table 4). 

Dowden (27) in a theoretical approach similar to that used for metals, has examined the probability of positive ion formation on intrinsic and extrinsic semiconductors. The energy of activation of this process in intrinsic semiconductors is considered to be proportional to ) where / is the ionization potential of the activated complex (/ + Ab ) the activation energy decreases as (exit work function) increases and as AF decreases, — defining the Fermi level. In the case of n- and p-type semiconductors, the Fermi level will... 

Morita et al. [222] compared bismuth molybdate (1/1) with U—Sb oxides (1 2) at 400°C in a continuous flow system. The methacrolein selectivity for U—Sb is significantly higher than in the case of Bi—Mo (see Table 20). These values increase slightly with increasing conversion of isobutene. Isobutene itself retards the oxidation. In contrast to the pro-pene oxidation, addition of steam accelerates the reaction up to a factor 4 with U—Sb and to a smaller degree with Bi—Mo. With the first catalyst, the activation energy decreases from 27 to 18 kcal mol-1 (0.23 atm steam). U—Sb seems to be less stable than Bi—Mo, but steam has a beneficial effect here too (Table 20). 

The apparent activation energies decrease in the order a > (3 > y >, etc. Typically, Eact (a) is several hundreds of kJ mol-1, whereas Eact ((3) is generally not higher than 100 kJmol 1, etc. 

The activation energy decreases with increasing light intensity I, following a... 

The activation energy decreases linearly with coverage, viz. 

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