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Need explanation for: - Equilibrium - JEE Main

An amount of solid NH_{4}HS is placed in a flask already containing ammonia gas at a certain temperature and 0.50\: atm pressure. Ammonium hydrogen sulphide decomposes to yield NH_{3} and H_{2}S gases in the flask. When the decomposition reaction reaches equilibrium, the total pressure in the flask rises to 0.85 atm. The equilibrium constant forNH_{4}HS decomposition at this temperature is

  • Option 1)

    0.30

  • Option 2)

    0.18

  • Option 3)

    0.17

  • Option 4)

    0.11

 
Answers (1)
105 Views
V Vakul

As we learnt in 

Relation between pressure and concentration -

PV=nRT

or\:P=\frac{n}{V}RT

or\:P=CRT

R=0.0831\:bar\:inter/mol\:K

- wherein

P is pressure in Pa. C is concentration in mol / litre. T is temperature in kelvin 

 

 

and

 

Law of Chemical equilibrium -

At a given temperature, the product of concentration of the reaction products raised to the respective stoichiometric coefficient in the balanced chemical equation divided by the product of concentration of the reactants raised to their individual stoichiometric coefficients has a constant value.

- wherein

aA+bB\rightleftharpoons cC+dD


K_{c}=\frac{[C]^{c\:[D]^{d}}}{[A]^{a}\:[B]^{b}}

[A],\:[B],\:[C]\:[D]

are equilibrium concentration

 

                                NH_{4}HS(s)\rightleftharpoons NH_{3}(g)+H_{2}S(g)

Initial pressure             0                                0.5                    0

At equi.                         0                            0.5 + x                  x

Total pressure = 0.5 + 2x = 0.84 

\therefore    x = 0.17 atm

K_{p}=p_{H_{3}}s\times p_{H_{2}}s=(0.5+0.17)(0.17)=0.11\ atm^{2}

 


Option 1)

0.30

This option is incorrect

Option 2)

0.18

This option is incorrect

Option 3)

0.17

This option is incorrect

Option 4)

0.11

This option is correct

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