TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The unit reactors comprise a frame formed from the process layers, perimeter barriers, or cavities. A portion of one of the reactant plenums is embedded in the reactor frame. The frame from a first unit reactor connects to a frame of the second unit reactor with a mechanical device. The inventive reactor further comprises a second process layer, a second perimeter barrier disposed on the second process layer, and a second cavity formed in reactor frame. The frames are held together by a protrusion and corresponding indentation formed from the frame that provides a snap fit connection, a mechanical clip, a tie rod, an adhesive bond, tape, external compression bands, and/or a key. The front perimeter barrier completely encloses the back cavity. The back perimeter barrier completely encloses the front cavity. The compact chemical reactor is a thin flat construction or thin curvilinear construction. There are 2-50000, preferably 2-500, and more preferably 2-100 unit reactors being used in the inventive reactor. Preferred Methods: The transport process is the exchange of reactant between the reactant plenums. It moves an attribute of the reactant from one of the reactant plenums to the other reactant plenum. The attribute is heat, moisture content, pressure, concentration, ionic charge, or electrical charge. Preferred Materials: The reactant comprises fuel, oxidant, water, hydrogen, oxygen, air, liquid phase hydrocarbons, gas phase hydrocarbons, beverages, foodstuffs, and/or byproducts from reaction of reactants. The process layers comprise an electrolyte, an ion exchange membrane a filtration membrane, a separation membrane, a micro-structured diffusion mixer, a heater, a catalyst, electrical conductors, and/or thermal conductors. They comprise a filled metal composite, a filled microstructure of polymer, a filled epoxy composite, and/or graphite composite. The cavity is filled with a material to aid in the transport of reactant or attributes of reactant or byproducts of the reaction. It is filled with a catalyst to promote the function of the reactor. Each perimeter barrier comprises a material (metal, silicone, rubber, polyamide, synthetic rubber, epoxy, polytetrafluoroethylene, polyvinyldifluoride, their composites, laminates, or alloys) that prevents reactant from one reactant plenum from moving into the other reactant plenum. Preferred Properties: The overall length of the compact chemical reactor is 1 mm to 100 cm and the overall width of the compact chemical reactor is 1 mm to 50 cm. The overall thickness between the front face and the back face of the compact chemical reactor is 100 nm to 5 cm. The compact chemical reactor has a shape consisting of rectangle, square, cylinder, triangle, octagon, pentagon, or irregular shape. The cavity has an aspect ratio greater than 1, preferably 1-100, and more preferably 2.5-15. The front and back perimeter barriers each comprise a height of 100 nm to 10 mm and a width of 10 nm to 5 mm.