Kinetic methods, advantages differential reaction-rate

The study and control of a chemical process may be accomplished by measuring the concentrations of the reactants and the properties of the end-products. Another way is to measure certain quantities that characterize the conversion process, such as the quantity of heat output in a reaction vessel, the mass of a reactant sample, etc. Taking into consideration the special features of the chemical molding process (transition from liquid to solid and sometimes to an insoluble state), the calorimetric method has obvious advantages both for controlling the process variables and for obtaining quantitative data. Calorimetric measurements give a direct correlation between the transformation rates and heat release. This allows to monitor the reaction rate by observation of the heat release rate. For these purposes, both isothermal and non-isothermal calorimetry may be used. In the first case, the heat output is effectively removed, and isothermal conditions are maintained for the reaction. This method is especially successful when applied to a sample in the form of a thin film of the reactant. The temperature increase under these conditions does not exceed IK, and treatment of the experimental results obtained is simple the experimental data are compared with solutions of the differential kinetic equation. 

The microanalytical methods of differential thermal analysis, differential scanning calorimetry, accelerating rate calorimetry, and thermomechanical analysis provide important information about chemical kinetics and thermodynamics but do not provide information about large-scale effects. Although a number of techniques are available for kinetics and heat-of-reaction analysis, a major advantage to heat flow calorimetry is that it better simulates the effects of real process conditions, such as degree of mixing or heat transfer coefficients. 

Although kinetic methods based on differential laws are more exact and more generally applicable, integrated rate laws have the advantage of being more rapid. In addition, in some cases the integrated rate equations can be used to describe the entire course of a chemical reaction. 

Although not very commonly used (with the exception of the initial rate procedure for slow reactions), the differential method has the advantage that it makes no assumption about what the reaction order might be (note the contrast with the method of integration, Section 3.3.2), and it allows a clear distinction between the order with respect to concentration and order with respect to time. However, the rate constant is obtained from an intercept by this method and will, therefore, have a relatively high associated error. The initial rates method also has the drawback that it may miss the effect of products on the global kinetics of the process. 

---