5I.15 Textbook Problem

[kyra sunil 3L]

Can someone help me start this question?

When solid NH4HS and 0.400 mol NH3(g) were placed in a vessel of volume 2.0 L at 24 °C, the equilibrium NH4HS(s)⇌NH3(g)+H2S(g), for which Kc=1.6×10−4, was reached. What are the equilibrium concentrations of NH3 and H2S?

[Luka Gogorishvili 1K]

First off, the best thing you can do when solving problems like these is start off with an ICE table to organize all the information you have into a readable form. For this particular question, you are given the same amount of the reactant and one of the products. Since the (Kc value * 1000) is less than the concentrations you are given, you can estimate and solve for Q which will then tell you what the changes in the concentrations are. You can exclude the concentration of the product from your calculations because it is a pure solid. So, the final K value = [NH3][H2S].

[Luka Gogorishvili 1K]

Sorry, if you look at the answer sheet, you don't actually need to know the Q value since the reactant is a pure solid, so the reaction will only proceed right.

[Michelle_Sen_3H]

So if you set up your ICE table you have the Initial concentrations as 0,.2,0 respectively, then for the change, it would be x, -x, and x, making the equilibrium line, x, .2-x, and x. If you solve for x (remember to leave out the solid) you should get .0008, which you can plug back into our table to find NH3 and H2S