Intrinsic activation energy values

In conjunction with this equation form, an intrinsic activation energy value of 122kJ/mol is listed.5 Kinetic control is most prevalent in small catalyst pellets, tablets, or rings having approximate volumes up to -0.3 cm3 each and internal surface areas of 60-80 m2/g.5... 

We emphasize that the often-quoted values of activation energies are apparent activation energies. For example, the rate of CH formation depends on the concentration of surface Ci species as well as on the concentration of surface hydrogen atoms, Hads- The apparent activation energy for "CH" formation from "Ci" is the intrinsic activation energy for... 

Nascimento in DFT cluster calculations. The computed intrinsic activation energy (45.16 kcal/mol) is in reasonable agreement with the value of... 

AGq = intrinsic activation energy barrier) which assumes values lower than 0.5 for concerted pathways, while for stepwise mechanisms, a results in values higher than 0.5. 

Thus, the elementary cellular structure could be regarded as an intrinsic characteristic of fhe detonation in a mixture at given initial composition, temperature, and pressure. The dimension of X is of fhe order of magnitude of millimeters or less for gaseous mixfures with oxygen, but several centimeters for less sensitive mixtures (even larger, for methane/air af afmospheric pressure). It decreases when the initial pressure increases. Its variation with the initial temperature is more complicated and depends on the value of fhe reduced activation energy of fhe chemical reactions. The value of... 

Under isothermal conditions, we have seen that the apparent activation energy of the reaction is approximately one half the intrinsic value when rj is sufficiently low. When rj exceeds unity, an opposite effect occurs (i.e., the apparent activation energy will exceed the true activation energy). 

For situations where the reaction is very slow relative to diffusion, the effectiveness factor for the poisoned catalyst will be unity, and the apparent activation energy of the reaction will be the true activation energy for the intrinsic chemical reaction. As the temperature increases, however, the reaction rate increases much faster than the diffusion rate and one may enter a regime where hT( 1 — a) is larger than 2, so the apparent activation energy will drop to that given by equation 12.3.85 (approximately half the value for the intrinsic reaction). As the temperature increases further, the Thiele modulus [hT( 1 — a)] continues to increase with a concomitant decrease in the effectiveness with which the catalyst surface area is used and in the depth to which the reactants are capable of... 

In very pure crystals, the number of intrinsic defects may be greater than the number of defects due to impurities, especially at high temperatures. Under these circumstances, the value of D0 will be influenced by the intrinsic defect population and may contribute to the observed value of the activation energy. 

Intrinsic free energy of activation for homogeneous self-exchange, obtained from values of corr giVen in Table 1 using AGih = "RT ln(kcorr/Zh) where 2 x 1()11, -1 ... 

However, the derived value for Ei is usually termed the activation energy E and may contain other contributions in addition to the intrinsic Ei value, such as those arising from the orientation and morphology of the sample. For this reason E is most commonly used. In the case of polycrystalline thin hlms, grain boundaries may have a dominant effect, as will be discussed in Section 6.4, where examples of intrinsically metallic materials behaving as semiconductors will be given. 

Increasing the impurity levels does not affect the intrinsic (left-hand side) of the graph. It does, however, increase the value of o (and thus of Ino) in the extrinsic region. As the activation energy, a, for cation movement stays the same, the slope... 

Consequently, the activation energy will be determined by means of the data obtained at 600 rpm, where the values of the observed rate represent the actual intrinsic rate. Since the reaction is of first order with respect to ethanol,... 

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