Solve the following problem:
Solid ammonium hydrosulphide (NH4HS) is mixed with arbitrary amounts of gaseous NH3 and H2S, forming a three-constituent system of two phases, undergoing the reaction
NH4HS ? NH3 + H2S.
(a) How many components are there, and what is the variance?
(b) Assuming that the gaseous phase is a mixture of ideal gases, show that
pNH3pH2S/pNH4HS = K .
(c) If solid NH4HS is placed in an evacuated chamber, how many components are there, and what is the variance?