A 100 L reaction container is charged with 0.612 mol of NOBr, which decomposes at a certain temperature** (say between 100 and 150 oC) according to the following reaction:

NOBr(g) ? NO(g) + 0.5Br2(g)

At equilibrium the bromine concentration is 2.12x10-3 M. Calculate Kc (in M0.5)

**Not specifying the temperature allows for a more liberal use of random numbers.

Respuesta :

Answer: The value of the equilibrium constant is 0.024

Explanation:

Initial moles of  [tex]NOBr[/tex] = 0.612 mole

Volume of container = 100 L

Initial concentration of [tex]NOBr=\frac{moles}{volume}=\frac{0.612moles}{100L}=6.12\times 10^{-3}M[/tex]  

equilibrium concentration of [tex]Br_2=2.12\times 10^{-3}M[/tex]

Equilibrium constant is the ratio of the concentration of products to the concentration of reactants each term raised to its stochiometric coefficients.

The given balanced equilibrium reaction is,

[tex]NOBr(g)\rightleftharpoons NO(g)+\frac{1}{2}Br_2(g)[/tex]

at t=0   [tex]6.12\times 10^{-3}M[/tex]     0       0

At eqm. conc. [tex](6.12\times 10^{-3}-x)M[/tex]      x       x/2     

The expression for equilibrium constant for this reaction will be,

[tex]K_c=\frac{[NO]^2[Br_2]}{[NOBr]}[/tex]

[tex]K_c=\frac{(2x)^2\times x/2}{(6.12\times 10^{-3}-x)}[/tex]

we are given : x/2 =[tex]2.12\times 10^{-3}[/tex]

Now put all the given values in this expression, we get :

[tex]K_c=\frac{(2.12\times 10^{-3})^{\frac{1}{2}}\times (2.12\times 10^{-3})}{(6.12\times 10^{-3})-(2.12\times 10^{-3})}[/tex]

[tex]K_c=0.024[/tex]

Thus the value of the equilibrium constant is 0.024