1. a) The equilibrium constant ( K c ) for the following reaction is 1.2 at 375

Question

1.

a) The equilibrium constant (Kc) for the following reaction is 1.2 at 375 oC. This reaction was initially started with 0.76 M H2, 0.60 M N2, and 0.48 M NH3. Is this system at equilibrium and if it is not which way will the net reaction proceed in order to reach equilibrium?

N2 (g)   + 3H2 (g)     ?     2NH3

b) For the following gas phase equilibrium reaction determine the partial pressure of PCl3 given that the system is at equilibrium at 500 K, Kp = 25, ????????5 = 0.15 atm, ??????2 = 0.20 atm.   

PCl5 (g) ? PCl3 (g) + Cl2 (g)

c) The equilibrium constant (Kc) for the following reaction is 1.00 X 10-5 at 1200 oC. If the reaction was initially started with 0.250 moles of N2 and 0.250 moles of O2 in a 2.0 L vessel, what is the equilibrium concentration of NO? (Hint: think ICE)

N2 (g)   + O2 (g)   ?     2NO (g)

Explanation / Answer

Solution:

a) Qc intiallly,

=> Qc = [NH3]^2 / [N2] [H2]^3

=> Qc = 0.48^2 / ( 0.60) (0.76)^3

=> Qc = 0.8747

and given Kc = 1.2

=> Kc > Qc hence the reaction will move in forward direction and system is not in equilibrium

b) Kp = p(PCl3) * p ( Cl2) / p(PCl5)

=> 25 = x * 0.20 / 0.15

=> x = 18.75 atm

c) let x be the concentration of NO

now, Kc = (2x)^2 / (0.25-x) ( 0.25-x)

=> 10^-5 * (0.25 -x)^2 = 4x^2

=> 10^-5 ( 0.0625 - 0.5 x + x^2 ) = 4x^2

=> 3.99999 x^2 + 0.5 * 10^-5 x - 0.0625 * 10^-5 = 0

=> x = 3.95 * 10^-4 moles

concentration x = 1.97 * 10^-4 M

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