A first-order, irreversible reaction takes place in two isothermal packed bed catalytic reactors; their lengths are 14 m and 21 m. This Demonstration compares the conversion, pressure, molar flow rate, and volumetric flow rate for the two reactors as a function of distance down the reactor. The inlet pressure is the same for each reactor and, for a given particle diameter, the outlet pressure is also the same. As a result, the flow rate into the longer reactor is lower. The Ergun equation is used to model the pressure drop; you can vary the diameter of the catalyst particles in the packed bed.