A method of recovering heavy oil from a subterranean heavy oil reservoir. The method includes conducting an exothermic chemical reaction of feedstock chemicals to produce a reaction product that that is a first solvent and injecting an injected solvent including the reaction product into the subterranean heavy oil reservoir. The injected solvent has an injected solvent temperature equal to an elevated temperature resulting from heat generated by the at least one exothermic chemical reaction and the injecting occurs before the injected solvent temperature has decreased to an ambient reservoir temperature.