Chemical reactor problems are formulated mathematically for plug flow reactors and CSTR (continuous stirred tank reactors). Illustrations include reactions with mole changes and temperature effects. Plug flow reactors are solved using MATLAB and FEMLAB, and CSTR reactors are solved using Excel and MATLAB. One example shows how to include mass transfer effects between the fluid and catalyst, another illustrates multiple steady state solutions in a CSTR, while another demonstrates a limit cycle in a CSTR.