For non-entangled Rouse chains undergoing the head-to-head association and dissociation reaction, the viscoelastic relaxation functions g1(t) and g2(t) were formulated analytically for a case that a dissociated unimer rapidly re-associates with its original partner. The relaxation of the unimer and dimer was essentially determined by ratios ra and rd of the association and dissociation times to the Rouse relaxation time in the absence of reaction. For small ra and rd (<< 1) the reaction was slow so that the unimer and dimer relaxed through respective pure Rouse modes, as naturally expected. However, for most cases in wide ranges of ra and rd, the dimer relaxation was accelerated with increasing rd (>> 1) and g2 of the dimer was indistinguishable from the pure Rouse relaxation function of the unimer, g1,Rouse. For those cases, g1 of the unimer also coincided with g1,Rouse. These results demonstrate that the motional coupling between the unimer and dimer, occurring through the association/dissociation reaction, strongly affects the relaxation. The Rouse modes of the unimer and dimer were found to split in two series due to this coupling, and new relaxation modes due to the coupling emerged as well. g1 and g2 were largely contributed from those new modes, thereby superficially agreeing with g1,Rouse for the cases of ra, rd >> 1. Keywords: Rouse model, Head-to-Head association/dissociation, Motional coupling