[lilmul123]

At 125°C, Kp = 0.25 for the following reaction.

2 NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)
A 1.00 L flask containing 11.9 g NaHCO3 is evacuated and heated to 125°C.

I've done part a of the problem:
(a) Calculate the partial pressures of CO2 and H2O after equilibrium is established.
(Both are .5 atm)

I'm now stuck on part b and c:

(b) Calculate the masses of NaHCO3 and Na2CO3 present at equilibrium.
Na2CO3:
NaHCO3 reacted:
NaHCO3 remaining:

(c) Calculate the minimum container volume necessary for all the NaHCO3 to decompose:

Now, my main thought is that I need to use an ICEbox starting from the molarity of NaHCO3 in order to find the molarities of the other compounds, and then converting to grams.  Sadly, I don't know how to start.  Can someone give me a push in the right direction?  Or am I wrong in my idea?

[Yggdrasil]

Instead of using molarity in your ICE box, why not use the number of moles?  Remember that you can calculate the number of moles of a gas by using the ideal gas law.