A device for evaporating at least one of the following reactants: a reducing agent precursor solution and a reducing agent precursor, includes at least one electrically heatable heating zone having at least one electrically operable heating element with a heating resistor that is self-regulated about a significant temperature. A method and the device for evaporating a reactant allow a simple control of an evaporation process, especially of a urea/water solution, to provide a reducing agent, especially in an SCR process. The heating resistors have a significant temperature that corresponds to a control temperature of the heating resistor. The need for additional control electronics can be removed by adjusting a correspondingly steep curve within a range.