In the hydrogenation of double bonds, a catalyst is needed. in the last step, the reactants must escape from the surface into the gas phase. this step is known as

 The  step  in which reactant  escape  from the surface into   the   gas phase is known as  desorption

   Desorption   is a phenomenon  whereby  a substance  is released   from  or through  a surface. One substance is released  from   another  either  from the surface or through  the surface. Desorption  can  occur  when   the system  is in the state  of  sorption  equilibrium  between bulk (fluid)   and  adsorbing  surface.(  boundary  separating two fluids)
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