Modifications are made to the standard process for the manufacture of ammonia and related compounds, resulting in lower operating costs through reduced total energy consumption. In one aspect of the invention, this is achieved by directing ammonia gas through one feed line, and carbon dioxide gas and steam through another feed line, into a closed reaction chamber to form ammonium carbonate. The formation of this solid compound results in a reduced pressure in the chamber. This reduced pressure can be used to drive heat engines in the reactant feed lines. In another aspect of the invention, the cost of running the potassium carbonate loop while the rest of the system is down is reduced by constructing an alternate pathway along part of the loop. The carbon dioxide gas and water vapor formed by the heating of the potassium bicarbonate flow through a heat engine and are cooled. The cooled water vapor and carbon dioxide gas are then recycled. The reactant gases may be liquified and revaporized in the event of reactor shutdown, and heat-exchange means may be associated with the system to provide at least a portion of the heat of vaporization of the liquified reactants. The heat-exchange means can thus produce a refrigerating fluid as a result of the vaporization of the reactants.