Question

At 21.8

Answer 1

The key here is that because NH4HS is a solid, its concentration does not show up in the Keq expression!

So, the equilibrium expression is:

Keq = [H2S][NH3] = 7.0 * 10^-2.

Now, from the chemical equation, we know that one mole of NH4HS produces one mole each of NH3 and H2S. So, at equilibrium, given that we started out with pure NH4HS, we must have equal amounts of NH3 and H2S. If we call the partial pressure of one of these x, we have:

Keq = x*x

7.0 * 10^-2 = x^2

---> x = 0.2646.

One minor detail you haven't included is the units for Keq. If the proper value of 7.0 * 10^-2 atm^2, then the final pressure for each gas is 0.2646 atm.

If the units are different (torr^2, bar^2, etc), then the value of 0.2646 will be in whatever those units are, and you may have to convert to atm afterwards.