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The temperature-pressure relations for the dissociation of solid ammonium carbamate into gaseous ammonia and carbon dioxide have been measured by several investigators. The reported values are divergent; at a total pressureof 40 atmospheres the divergence is as much as 17 atmospheres.
Briggs and Migrdichian measured the dissociation pressure of ammonium carbamate over temperature range 10 oC to 45 o C and obtained very consistent data. They also studied the effect of excess ammonia or carbon dioxide and found excellent agreement with the mass law according to the equation:


Carbamate (sold) = 2 NH3(gas) + CO2(gas)

 

The present paper covers a study of the dissociation pressure of solid ammonium carbamate over the temperature range 35 oC to 83 oC and in the absence of an excess of either gaseous reactant. From the vapor pressure data the free energy of dissociation and the heat of dissociation have been derived.