The adsorption and chemical transformation of iodoethane were studied on a Si(100)-2x1 surface using multiple-internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR). The C-H and Si-H stretch vibrations served as fingerprints of all surface transformations. Although ethyl groups are stable on the Si(100)-2x1 surface at room temperature, thermal annealing studies suggest the reaction-limited formation of ethylene, a major hydrocarbon reaction product, accompanied by the loss of hydrogen, which is left on the surface until the temperature of recombinative H-2 desorption is reached. Variable temperature studies indicate that ethyl groups are the only hydrocarbon entities on a surface up until the hydrogen elimination temperature. The positions of Si-H stretching bands suggest that a mixture of surface sites is formed at temperatures between 300 K and 600 K. However, the majority of surface hydrogen forms SiH-SiI surface species as the surface temperature reaches 700 K.