The adiabatic tubular or batch reactor

For a batch reactor the very definition of reaction rate gives the equation 

The simplest model of the tubular reactor is that the stream flows uniformly through the reactor with 

For gas reactions when the density may vary throughout the bed, the mass fraction is sometimes to be preferred above the molar concentration in representing the composition. Then, if G is the mass flow rate per unit cross-sectional area of reactor and g/z) the mass fraction of A, at z, a mass balance for unit time and unit area gives 

We have made the reaction rate a function of pressure as well as of temperature and extent per unit mass, for this representation is most useful with gas reactions for which pressure may be an important factor. If density is constant we recover Eq. (8.4.7) by setting G = pv and f= /p. 

For ideal gases or when enthalpy is not very dependent on pressure, the total enthalpy per unit mass is If this is constant for adiabatic 

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