Rate of conversion

For homogeneous reactions we obtain the conventional definition of the reaction rate u. as rate of conversion per volume... 

The equilibrium constant for this reaction decreases with increase in temperature but the higher temperature is required to achieve a reasonable rate of conversion. Hydrogen chloride is now being produced in increasing quantities as a by-product in organic chlorination reactions and it is economic to re-convert this to chlorine. 

Chemists are interested not only in the thermodynamics of a process (the relative stability o the various species) but also in its kinetics (the rate of conversion from one structure tc another). Knowledge of the minimum points on an energy surface enables thermodynamic data to be interpreted, but for the kinetics it is necessary to investigate the nature of the... 

Dry potassium cyanide in sealed containers is stable for many years. An aqueous solution of potassium cyanide is slowly converted to ammonia and potassium formate the decomposition rate accelerates with increasing temperature. However, at comparable temperatures the rate of conversion is far lower than that for sodium cyanide only about 25% as great. 

An increase in temperature will increase the values of and k. In practice it is observed that in free-radical-initiated polymerisations the overall rate of conversion is approximately doubled per 10°C rise in temperature (see Figure 2.20). Since the molecular weight is inversely related to k and k it is observed in practice that this decreases with increase in temperature. 

An increase in initiator concentration or in temperature will increase the rate of conversion but decrease molecular weight. 

Transfer reactions will reduce the degree of polymerisation without affecting the rate of conversion. 

An increase in the rate of radical production in emulsion polymerisation will reduce the molecular weight since it will increase the frequency of termination. An increase in the number of particles will, however, reduce the rate of entry of radicals into a specific micelle and increase molecular weight. Thus at constant initiator concentration and temperature an increase in micelles (in effect in soap concentration) will lead to an increase in molecular weight and in rate of conversion. 

It has been observed that in the polymerisaton of methyl methacrylate there is an acceleration in the rate of conversion after about 20% of the monomer has been converted. The average molecular weight of the polymer also increases during polymerisation. It has been shown that these results are obtained even under conditions where there is a negligible rise in the temperature (<1°C) of the reaction mixture. 

Fig. 1.13 Block on inclined plane illustrating the relationship between the thermodynamic tendency — AG) of a corrosion reaction aA + bB cC + dD and the rate of conversion of metal A to corrosion products C and D...

The rate at which A is converted to D (the overall reaction) is approximately equal to the rate of conversion of B to C (the slow step). 

Specific information about the optimum conditions for the synthesis and the activity of the enzyme has been reported for Pseudomonas fluorescens screening of various micro-organisms resulted in the selection of a P. fluorescens strain with an initial rate of conversion of 3 g P h 1 in an imoptimised state. The following conclusions could be made concerning the production of L-phenylalanine by P. fluorescens ... 

Similar anomalies have been encountered by several workers in the bulk and solution polymerization of this monomer induced by classical free-radical initiators84-86) also, particularly low rates of conversion were observed. The most thorough kinetic study was carried out by Aso and Tanaka86) who again found normal results and a value of k jkt much lower than that for styrene. Copolymerization studies of 2-vinylfuran (Mj) have given the following values of the reactivity ratios ... 

Fig. 5. Effect of the nature of adjacent functional groups in copolymers on the rate of conversion of the nitrile groups into thioamide groups. (1) PAN (2) AN-VDC (3) AN-AA (4) AN-MA (5) AN-VC (6) AN-ST...

Improve Rate of Conversion. Increasing the activity of a catalyst may allow either higher output from a plant or operation of the plant under less arduous conditions thereby alleviating the constraints which limit the economic improvement of the process. 

The authors stated at the beginning of their work that to understand the mechanism of the reactions studied required an unambiguous determination of the influence of the hydrogen pressure on the rate of conversion or equilibration reactions. This could be possible only when dealing with a palladium catalyst incapable of absorbing hydrogen, i.e. with the palladium samples previously fully transformed into the /3-hydride phase, in which the H/Pd ratiq would be constant, almost independent of the hydrogen pressure. Then, for example, at room temperature under p = 1 atm, H/Pd = 0.68 when under p = 10 atm, H/Pd = 0.70 and under p = 1000 atm, H/Pd = 0.80 only. 

What Are the Key Ideas Equilibrium between two phases is reached when the rates of conversion between the two phases are the same in each direction. The rates are equal when the molar Gibbs free energy of the substance is the same in each phase and therefore there is no tendency to change in either direction. The same concepts apply to the dissolving of a solute. The presence of a solute alters the entropy of a solvent and consequently affects its thermodynamic properties. 

When chain transfer is considered and following the derivation previously given (1, 2) the instantaneous rate of conversion is then given by... 

It can be seen from equation (2) that when y 0 the model falls into the classical expression for the rate of conversion of free radical polymerization. Equation (la) shows that this will be the case whenever all macroradicals have the same high mobility (i.e., as n tends to infinity) or when both entangled and non-entangled radicals have the same termination rate constant (i.e. a is equal to unity). 

Experimental conversion-time data, obtained from the literature, on the bulk free radical polymerization of MMA initiated by AIBN at several temperatures and initiator concentrations, were described by the model. However, the expressions for the rate of conversion and gel effect index were first simplified and rearranged. ... 

Once the copolymerisation reaction has become properly established, the radical chains A- and B- each achieve a steady-state concentration. The absolute rate of conversion of A- to B- and of B- to A- becomes the same ... 

Jones (refs. 11,12) subsequently investigated the relative reactivities of the various cobalt(III) species with Br, Mn and H2O2. The active p-oxodimer, Co was two to four orders of magnitude more reactive than Co which was four to five times more reactive than (Fig. 13). Furthermore, it should be noted that the rate of conversion of Co to Co is much higher than the rate of reaction of Co with ArCH3. In other words, in the absence of Br or Mn the cobalt species that reacts with ArCH3 cannot be Co. ... 

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