Low-energy electron microscopy (LEEM) and micro-LEED (micro low-energy electron diffraction, beam diameter 1 mu m) have been employed to resolve the structural changes which occur during chemical wave propagation in the system Rh(110)/NO + H-2. In a pulse the surface undergoes cyclic structural transformations in the sequence c(2 x 6)-O, (3 x 1)-N, (2 x 1)-N, c(2 x 4)-20,N, c(2 x 6)-O. In situ dark field imaging with superstructure beams was used to demonstrate the contribution of the various reconstruction phases to pulse propagation. Based on the LEED/LEEM results, an excitation mechanism is proposed.