EK Chem 1001 Q287 (i typed the question out for others)

[XsmallX]

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I don't know if i'm wrong (and if i am please tell why i'm wrong😳) or if the book is wrong, so here's the question:

Consider the following endothermic reaction:
NH4HS (s) <=> NH3 (g) + H2S(g)

If the system were at equilibrium within a sealed container, which of the following would produce addition H2S?

I. Raising the temperature
II. Adding more NH4HS
III. Increasing the volume of the container.

I thought it was all three, but EK says its only I and III because the solid will not effect the equilibrium...I know when we're writing equilibrium constants solids and liquids are not included, BUT if there's more solid won't it react with the heat and make more H2S?😕

 

[tartrate]

It's been a while, but let's see...

It seems #2 is trying to confuse you by invoking the le chatelier's principle.

In terms of solids and gasses, I think it is an approximation that there is a lot more solid than gas can possibly be produced in that container. So that means it will never be the limiting reagent, and the jar will only hold as much gas as its container is willing to tolerate (via pressure). So while expanding and heating increases the sublimation of the solid into gas, simply adding more of the solid won't do anything, in this equilibrated, sealed environment.

 

[latrala2300]

pure solids and pure liquids are never part of equilibrium or eq. expressions.

so if you see equilibrium, you may as well start by crossing out the solids and liquids in the original problem. i hate this i always forget 😡

 

[XsmallX]

ah, okay got it. So basically liquids and solids do nothing for shifting the equilibrium for gases cause they're not part of the equation...hmm yeah tartrate makes a lot of sense. I never thought of it that way!