At sufficiently high temperatures, ammonium iodide decomposes to ammonia and hydrogen iodide.
NH4I(s) NH3(g) + HI(g)
A mass of 5.00 g of NH4I is sealed in a 2.00-L flask and heated to 673 K. If 2.56 g NH4I(s) remain unreacted when the system has reach equilibrium, what is the equilibrium constant (Kp) for the reaction? (R = 0.0821 Latm/molK)

Question

At sufficiently high temperatures, ammonium iodide decomposes to ammonia and hydrogen iodide. 
NH4I(s) NH3(g) + HI(g) 
A mass of 5.00 g of NH4I is sealed in a 2.00-L flask and heated to 673 K. If 2.56 g NH4I(s) remain unreacted when the system has reach equilibrium, what is the equilibrium constant (Kp) for the reaction? (R = 0.0821 Latm/molK)

confusionist · Answer

Yo. Copy+Paste or whatever you used doesn't do the trick. You're missing part of the equation. Try screenshotting in the future. 
In this whole thing you've posted: NH4I(s) NH3(g) + HI(g)  You're missing the yield. Right now it looks like some weird "NH4I(s) + NH3(g) + HI(g) = ?" kind of thing. 

Anyway, your answer is .22.