DETERMINING EXPERIMENTAL RATE EQUATIONS AT A FIXED TEMPERATURE

DETERMINING EXPERIMENTAL RATE EQUATIONS AT A FIXED TEMPERATURE... 

Determining experimental rate equations at a fixed temperature... 

As we have seen, in order to determine the form of the experimental rate equation for a chemical reaction it is necessary to carry out experiments at a fixed temperature. This is to avoid any complications due to the rate of reaction changing as a function of temperature. In general, it is the rate constant, / r, for a chemical reaction that is temperature-dependent and this is illustrated in Figure 6.1 for the reaction between iodomethane (CH3I) and ethoxide ion (C2H50 ) in a solution of ethanol... 

The spatial distribution of composition and temperature within a catalyst particle or in the fluid in contact with a catalyst surface result from the interaction of chemical reaction, mass-transfer and heat-transfer in the system which in this case is the catalyst particle. Only composition and temperature at the boundary of the system are then fixed by experimental conditions. Knowledge of local concentrations within the boundaries of the system is required for the evaluation of activity and of a rate equation. They can be computed on the basis of a suitable mathematical model if the kinetics of heat- and mass-transfer arc known or determined separately. It is preferable that experimental conditions for determination of rate parameters should be chosen so that gradients of composition and temperature in the system can be neglected. 

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