Ammonium bisulfide, NH4HS, forms ammonia, NH3, and hydrogen sulfide, H2S, through the reaction
NH4HS(s)⇌NH3(g)+H2S(g)
This reaction has a Kp value of 0.120 at 25 ∘C.
An empty 5.00-L flask is charged with 0.350 g of pure H2S(g), at 25 ∘C.
What is the initial pressure of H2S(g) in the flask?
mols H2S = grams/molar mass = 0.350/34 = 0.0102
Then PV = nRT.
P = nRT/V = [0.0102*0.08206 x (273+25)]/5.00 = ? atm
To calculate the initial pressure of H2S(g) in the flask, we need to use the ideal gas law equation, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature in kelvin.
1. Convert the temperature from Celsius to Kelvin:
T(K) = T(°C) + 273.15
T = 25°C + 273.15 = 298.15 K
2. Convert the mass of H2S(g) to moles:
We need the molar mass of H2S to convert grams to moles. The molar mass of H2S is approximately 34.08 g/mol.
n = m/M
n = 0.350 g / 34.08 g/mol = 0.01026 mol
3. Calculate the initial pressure of H2S:
P = nRT/V
Here, V is the volume of the flask, which is given as 5.00 L.
R is the ideal gas constant, which is 0.0821 L atm/mol K.
P = (0.01026 mol)(0.0821 L atm/mol K)(298.15 K) / 5.00 L
P = 0.0487 atm
Therefore, the initial pressure of H2S(g) in the flask is 0.0487 atm.