In this paper we reported that low temperature plasma may reverse the direction of a chemical reaction. The thermodynamically forbidden reaction between H-2 and AlCl3 was able to take place with the assistance of low temperature plasma, yielding metal Al. The plasma chemistry of the reaction was investigated by optical emission spectroscopy, which suggested that the dissociation of H-2 and AlCl3 molecules by plasma led the reaction to a thermodynamically favorable one by creating reaction channels with low Gibbs free energy change. The addition of Ar promoted the reaction kinetics dramatically, which was attributed to the enhanced dissociation of AlCl3 molecules by excited Ar species.