Most current rockets are chemically powered rockets (usually internal combustion engines, but some employ a decomposing monopropellant) that emit a hot exhaust gas.
Chemically, it is a chlorotriazine; compared with atrazine and simazine, it has a tert-butyl group in place of the isopropyl and ethyl groups, respectively.
Alternatively, a chemically inert reaction mass can be heated using a high-energy power source via a heat exchanger, and then no combustion chamber is used.
