The Scope of Chemical Reaction Engineering

The two questions that must be answered for a chemically reacting system are (1) what changes are expected to occur and (2) how fast will they occur The initial task in approaching the description of a chemically reacting system is to understand the answer to the first question by elucidating the thermodynamics of the process. For example, dinitrogen (N2) and dihydrogen (H2) are reacted over an iron catalyst to produce ammonia (NH3)  

In order to obtain a reasonable level of conversion at a commercially acceptable rate, ammonia synthesis reactors operate at pressures of 150 to 300 atm and temperatures of 700 to 750 K. Calculate the equilibrium mole fraction of dinitrogen at 300 atm and 723 K starting from an initial composition of = 0.25, Xh, = 0.75 (X, is the mole fraction of species i). At 300 atm and 723 K, the equilibrium constant, K , is 6.6 X 10. (K. Denbigh, The Principles of Chemical Equilibrium, Cambridge Press, 1971, p. 153). 

Upon obtaining each from correlations or tables of data (available in numerous references that contain thermodynamic information)  

1 and = (25 — 13.1)/(100 - 26.2) = 0.16. At 300 atm, the equilibrium mole fraction of ammonia is 0.36 while at 100 atm it falls to approximately 0.16. Thus, the equilibrium amount of ammonia increases with the total pressure of the system at a constant temperature. 

If a step of the sequence can be written as it proceeds at the molecular level, it is denoted as an elementary step (or an elementary reaction), and it represents an irreducible molecular event. Here, elementary steps will be called steps for short. The hydrogenation of dibromine is an example of a stoichiometrically simple reaction  

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