In this study, the characteristic behavior of a rotating arc was investigated. Various modes, depending on the electric power supplied, can be observed in a rotating arc. Each mode produces different discharge characteristics and thermal environments and, accordingly, chemical processes hosted in the plasma reaction volume can be controlled differently in each mode. General thermal to non-thermal transitions observed in a gliding arc are based on the longitudinal expansion of the arc column. In a rotating arc, the reverse transition or non-thermal to thermal transition can be hosted by controlling the reactor geometry. The reverse transition can be achieved by self-adjustment of the arc column where longitudinal expansion of the arc column is confined. The reverse transition enhances the conversion efficiency of electric power to thermal energy. Then, optimization of thermal activation was obtained by controlling the mode of operation, and it was verified using the NH3 decomposition reaction.