Question

1) Ammonium bisulfide, NH4HS, forms ammonia, NH3, and hydrogen sulfide, H2S, through the reaction

NH4HS(s)⇌NH3(g)+H2S(g)

This reaction has a K value of 0.120 at 25 ∘C.

an empty 5.00-L flask is charged with 0.400 g of pure H2S(g), at 25 ∘C.

What is the initial pressure of H2S(g) in the flask?

Answer 1

Mass of H₂S in the flask = 0.400 g

Molar mass of H₂S = 34.1 g/mol

Moles of H₂S in the flask (n) = mass of H₂S in the flask /molar mass of H₂S

                                          = 0.400 g/34.1 g/mol

                                          = 0.0117 mol

Volume occupied by the gas (V) = 5.00 L

Temperature of the gas (T) = 25 ^oC = (25 + 273) K = 298 K

Now, from ideal gas law,

PV = nRT

where,

P = pressure of the gas

R = gas constant = 0.082 L.atm/mol.K

Thus,

or, P x 5.00 L = 0.0117 mol x 0.082 L.atm/mol.K x 298 K

or, P = 0.0572 atm

Hence, the initial pressure of H₂S(g) in the flask = 0.0572 atm