At an elevated temperature, Kp=4.2 x 10^-9 for the reaction 2HBr (g)---> +H2(g) + Br2 (g). If the initial partial pressures of HBr, H2, and Br2 are 1.0 x 10^-2 atm, 2.0 x 10^-4 atm, and 2.0 x 10^-4 atm, respecivtely, what is the equilbrium partial pressure of H2?

Answer : The partial pressure of at equilibrium is, 1.0 × 10⁻⁶

Explanation :

The partial pressure of =

The partial pressure of =

The partial pressure of =

The balanced equilibrium reaction is,

Initial pressure    1.0×10⁻²       2.0×10⁻⁴      2.0×10⁻⁴

At eqm.            (1.0×10⁻²-2p)   (2.0×10⁻⁴+p)  (2.0×10⁻⁴+p)

The expression of equilibrium constant for the reaction will be:

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

The partial pressure of at equilibrium = (2.0×10⁻⁴+(-1.99×10⁻⁴) )= 1.0 × 10⁻⁶

Therefore, the partial pressure of at equilibrium is, 1.0 × 10⁻⁶

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