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Question

At 25 degrees C:

NH4HS(s) <--> nnh3 (G) +H2S (g)

has Kp=0.120. A 5.00 L flask is charged with 0.300 g of pure H2S (g) at 25 degrees C. Solid NH4HS is then added until there is excess unreacted solid remaining.

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

(b) Why does no reaction occur until NH4HS is added?

(c) What are the partial pressure of NH3 and H2S at equilibrium?

(d) What is the mole fraction of H2S in the gas mixture at equilibrium?

(e) What is the minimum mass, in grams, of NH4HS that must be added to the flask to achieve equilibrium?

Answer 1

Step 1:

The volume of the flask is V = 5.0 L.

Equilibrium constant .

Temperature of the hydrogen sulfide is 25°C.

Temperature in Kelvin = 25°C + 273 = 298 K.

Amount of hydrogen sulfide is 0.300 g.

Convert grams into moles.

Molecular mass of the hydrogen sulfide is 34.0809 g/mol.

Number of moles of hydrogen sulfide is n= .

(a)

Find the initial pressure of hydrogen sulfide.

Ideal law of gas: , where

P  is the pressure (in atm),

V  is the volume of gas (in Litre) ,

n is the chemical amount of the gas (moles) ,

R is universal constant = 0.082 (L atm)/(K mol)

and T  is the temperature (kelvins).

Initial pressure of hydrogen sulfide 0.0392 atm.

Step 2:

(b)

The reaction will not occur.

As the Ammonium hydro sulfide is added, the reaction will reach the equilibrium state.

Hence, no reaction takes place until Ammonium hydro sulfide is added.

Solution :

(a) Initial pressure of hydrogen sulfide 0.0392 atm.

(b) If ammonium hydro sulfide is not added then the reaction will not reach equilibrium state and no reaction takes place.

Comments

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Answer 2

Step 1:

(c)

The chemical equation is .

Equilibrium constant is

, where , and are the partial pressures.

Let x be the change in pressure.

Partial Pressure = Initial Pressure + Change in Pressure

Partial Pressure of hydrogen sulfide = 0.0392 + x

Partial Pressure of Ammonia =  x

Partial pressure of Ammonium hydro sulfide is 1.   (Since it is a solid substance)

Partial pressure cannot be negative then .

Partial Pressure of hydrogen sulfide = 0.0392 + 0.327 = 0.3662 atm.

Partial Pressure of Ammonia =  0.327 atm.

Step 2:

(d)

Total Pressure of the gas is 0.3662 + 0.327 = 0.6932 atm.

Find the mole fraction of hydrogen sulfide.

Mole fraction and Partial pressure relationship:

where

is the mole fraction of the individual gas.

is the partial pressure of the individual gas.

is the total pressure of the mixture.

Mole fraction of hydrogen sulfide is 0.5283.

Solution :

(c)

Partial Pressure of hydrogen sulfide = 0.3662 atm.

Partial Pressure of Ammonia =  0.327 atm.

(d) Mole fraction of hydrogen sulfide is 0.5283.

Answer 3

Step 1:

(e)

Pressure of ammonia = 0.327 atm.

Now we calculate the mass of ammonia here using ideal gas equation.

Ideal law of gas: .

Minimum mass of the Ammonium hydro sulfide:

0.0669 moles of Ammonia is equal to 1 mole of Ammonium hydro sulfide.

Minimum mass of Ammonium hydro sulfide is 3.4119 grams.

Solution :

(e) Minimum mass of Ammonium hydro sulfide is 3.4119 grams.