Textbook 5I. 33

[kiara chan]

A sample of Nh4(Nh2CO2) of mass 25 g was placed in an evacuated flask of volume 0.250 L and kept at 25 celsius. At equilibrium 17.4 mg of CO2 was presented what is the value of Kc given that NH4(NH2CO2)(s) = 2NH3 (g) + CO2

I understand that the equilibrium constant will only include NH3 and CO2, but how will i find the x value?

[Shria G 2D]

Hi,
I believe you don't have to solve for x in an equation like we typically do because you can figure it out from what is given. Since only NH3 and CO2 are in the equilibrium constant and they are both products, their initial concentration is 0. We just need to find the equilibrium concentration of CO2 which can be done by converting 17.4 mg to moles by using the fact that the molar mass of CO2 is 44.01 g/mol. Concentration is moles of solute divided by liters of solution so if you divide the moles CO2 by 0.250 L, you get concentration. That value is also equal to change for CO2 since its initial concentration is 0. The change for NH3 would be twice that value because of the stoichiometric coefficient. Kc = [CO2][NH3]^2 so you can plug in the concentration values you found to find the equilibrium constant. I hope that helps!

[Anne Hogue 2J]

Hi! To solve this you first need to convert mg to g of CO2 and then divide by the molar mass of CO2 to get moles. Then for NH3, you need to multiply this value by 2 because there are 2 NH3 and only one CO2. You can then multiple these answers to get Kc and divide by the volume. Hope this helps!