A device and a method for providing a gaseous substance mixture including at least one of a reducing agent and/or a reducing agent precursor, include a reservoir for an aqueous solution including at least one reducing agent precursor, from which the aqueous solution can be delivered into at least one metering line having a dispensing opening by a delivery device, and a device for heating the metering line above a critical temperature greater than the boiling temperature of water. Complete evaporation of an aqueous solution including urea and subsequent hydrolysis to form a substance mixture including ammonia, are carried out. The substance mixture is metered as a reducing agent into an SCR catalytic converter. Carrying out the evaporation outside the exhaust system uses considerably smaller hydrolysis catalytic converters, which is space-saving and cost-saving compared to conventional devices for providing a reducing agent for selective catalytic reduction of nitrogen oxides.