5I.33

[Deena Doan 2F]

5I.33 A sample of ammonium carbamate, NH4(NH2CO2), of mass 25.0 g was placed in an evacuated flask of volume 0.250 L and kept at 25 8C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The reaction is
NH4(NH2CO2)(s) -> 2NH3(g) + CO2(g).

Can someone help me with this problem?

[Victoria Zheng--2F]

For this question, the first step is to find the concentration of both ammonium carbamate and CO2 by finding the molarity of the two molecules. The concentration of ammonium carbamate is 1.28M, and the concentration of CO2 is 3.95*10^-4M. Then, set up an ICE table with initial concentrations 1.28, 0, 0, change in concentrations -x, +2x, +x, and equilibrium concentrations 1.28-x, 2x, x. Since the equilibrium concentration of CO2 is 1.58*10^-3M, x in the ICE table would be 1.58*10^-3M. Then, solve for the equilibrium concentrations of NH3 and ammonium carbamate, which are 1.278 and 3.16*10^-3M. Then, arrange the equation to calculate equilibrium constant, and since ammonium carbamate is solid, it won't be included in the calculation. The final equilibrium constant is 1.58*10^-8.