A new vapour-cracking transformation process for organic compsns. using super-heated and activated water vapour obtd. by an electrical plasma discharge and used to initiate and sustain chemical reactions is disclosed.    Also claimed is an appts. comprising a plasma generating reactor, fluid injecting devices, heat exchangers and devices for regenerating effluent.    Pref. the superheated and activated water vapour is obtd. at a moderate pressure, 50 torr-5.5 bars. It is decomposed to atomic, ionic and radical species. The fluid or gases to be treated may be mixed with water vapour before treatment. Compsns. to be treated include liqs. and esp. gas, gas mixts. and vaporisable compsns.. The treatment temp. is lower than the calculated thermodynamic value - as the plasma generator functions outside thermodynamic equilibrium values. The prods. of the treatment of the compsns. contain carbon monoxide and hydrogen, and opt. simple unsatd. hydrocarbons, esp. acetylene and ethylene, and opt. acid halides.    USE -   The process can be used to transform any hydrocarbon (HC), including methane, into 'synthesis gas' (mainly CO and H2), without the aid of a catalyst - by the reaction: CH4 + H2Ovap CO + 3H2 (1). It can also be applied to the transformation of other organic moles, notably CFC's and highly halogenated cpds. (such as CHCl3 and 'Freon 12'): in the hydro-pyrolysis of these cpds. some O2 is formed - possibly by decomposition of H2O and CO2: H2) H2 + O2 (13), CO2 CO + O2 (14) accompanied by a 'shift' reaction: CO + H2O CO2 + H2 ( = in equilibrium with). Aq. solns. of HCl and/or HF may opt. be recovered from the process.    ADVANTAGE -   The invention provides gases rich in H2, mists. of CO and H2, and mixts. of CO, H2, C2H2 and C2H4. The process can be carried out without the intervention of other reactants or catalysts and avoiding prodn. of soot or coke which would limit the life of the electrodes. The 'gliding arc' technique of the plasma generator enables efficient transfer of electrical energy in an endothermic medium without the need for preionisation of the medium. The energy costs for the vapour cracking of CH4 by this process are lower than the classical prodn. of H2 in water electrolysis installations.