Ammonium hydrogen sulphide dissociates as follows `:`
`NH_(4) HS(s) hArr H_(2) S(g) = NH_(3)(g)`
If solid `NH_(4) HS` is placed in an evacuated flask at a certain temperature, it will dissociate until the total gas pressure is 500 torr. Calculate the following `:`
( a) Equilibrium constant for the dissociation reaction
( b) If the additional `NH_(3)` is introduced into the equilibrium mixture without change in temperature until the partial pressure of ammonia is 700 torr.
(i) What is the partial pressure of `H_(2)S` under the conditions.
(ii) What is the total pressure in the flask ?

Explanation

Since, `P_(H_(2)S) = P_(NH_(3)) = ( 250)/( 760) = 0.329 `atm
( a) `K_(p ) =P_(H_(2)S) P_(NH_(3)) = 0 .108"atm"^(2)`
( b) `K_(p ) = P_(H_(2)S ) P_(NH_(3))`
`P_(H_(2)S) = ( 0.108)/( 700 // 760 ) = 0.117` atm
(ii) Total pressure `= P_(H_(2) S) + P_(NH_(3)) = 789 ` torr