Question

46. At some temperature, the Kc is 0.09 for the
reaction 2NO = N2 + O2. How many moles of
NO must be taken in 1 litre flask to obtain
equilibrium concentration of N2= 0.2 M?
(1) 0.25
(2) 0.93
(3) 0.4
(4) 1.067​

Answer 1

Answer:

,

Explanation:

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Answer 2

1.067 moles of NO must be taken in 1 litre flask. Hence the correct option is (4) 1.067.

Given:

Kc = 0.09

The volume of the flask (V) = 1 litre

The equilibrium concentration of N₂ = 0.2 M

To Find:

→ The equilibrium constant (Kc) is equal to the ratio of the equilibrium concentrations of the products to the equilibrium concentrations of reactants each of them raised to the power of their stoichiometric coefficients.

For a reaction: aA + bB → cC + dD

The value of the equilibrium constant (Kc) would be given as:

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

→ For the reaction:     2NO ↔ N₂ + O₂

The value of the equilibrium constant (Kc) would be given as:

                                          $\boldsymbol{K_{c} =\frac{[N_{2} ] [O_{2} ]}{[NO]^{2} } }$

→ In the given reaction:

Let the molar concentration of NO that must be taken be 'a'.

                                         2NO ↔ N₂ + O₂

                         Initially:   a M       0       0

             At equilibrium: (a - 2x)    x        x    

→ The equilibrium concentration of N₂ is equal to 0.2 M. Therefore we can say that 'x' is equal to 0.2 M.

The value of the equilibrium constant (Kc) would be given as:

                                      $\boldsymbol{\therefore K_{c} =\frac{[N_{2} ] [O_{2} ]}{[NO]^{2} } }\\\\\boldsymbol{\therefore K_{c} =\frac{[x ] [x ]}{[a-2x]^{2} }}\\\\\boldsymbol{\therefore K_{c} =\frac{[0.2 ] [0.2 ]}{[a-2(0.2)]^{2} }}\\\\\boldsymbol{\therefore 0.09=\frac{[0.2 ]^{2} }{[a-0.4]^{2} }}\\\\\boldsymbol{\therefore 0.3=\frac{[0.2 ] }{[a-0.4] }}\\\\\boldsymbol{\therefore 0.3a-0.12=0.2}\\\\\boldsymbol{\therefore 0.3a=0.32}\\\\\boldsymbol{\therefore a=1.067\:M}$

→ The value of 'a' comes out to be equal to 1.067 M.

Since the volume of the flask is equal to 1 litre, therefore the number of moles of NO that must be taken is equal to 1.067 moles.

Therefore 1.067 moles of NO must be taken in 1 litre flask. Hence the correct option is (4) 1.067.

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