If a particular process is endothermic, the reverse process must be an exothermic process. This is because, when the endothermic process occurs, the substance takes energy from its surroundings. The reverse of this reaction would be for the substance to release energy into its surrounding. Therefore, the answer is exothermic.
If a particular process is endothermic, there can be no assurance that the reverse process is exothermic, since some exothermic processes do not occur at certain pressures and temperatures. In general, the pressure and temperature conditions under which the reverse process is performed should be established.
