Ammonium bisulfide, NH4HS , forms ammonia, NH3 , and hydrogen sulfide, H2S , thr

Question

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 .

Part A

Evaluate the validity of the following statements as true or false

A. The reaction proceeds to the right.

B. The pressure of ammonia is zero.

C. Q is equal to 0.

D. The reaction proceeds to the left.

E. Q is greater than K.

F. No reaction occurs.

Part B

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

Express your answer numerically in atmospheres.

Explanation / Answer

For the given decomposition reaction,

NH4SH(s) <==> NH3(g) + H2S(g)

Kp = [(pNH3)(pH2S)]

      = 0.120

Part A) When an empty 5 L flask is charged with 0.350 g of pure H2S

The statements valid for this system would be,

A. The reaction proceeds to the right : False.

B. The pressure of ammonia is zero : False.

C. Q is equal to 0 : False.

D. The reaction proceeds to the left : False.

E. Q is greater than K.

F. No reaction occurs : True

Part B) The initial pressure of H2S(g) in the flask would be,

moles of H2S = 5/34.1

                       = 0.15 mol

V = 5 L

T = 273 + 25 = 298 K

Using,

P = nRT/V

we get,

Initial pressure of H2S = 0.15 x 0.08205 x 298/5

                                     = 0.733 atm

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