Xas shown in table 15.2, kp for the equilibrium n21g2 + 3 h21g2 δ 2 nh31g2 is 4.51 * 10-5 at 450 °c. for each of the mixtures listed here, indicate whether the mixture is at equilibrium at 450 °c. if it is not at equilibrium, indicate the direction (toward product or toward reactants) in which the mixture must shift to achieve equilibrium. (a) 98 atm nh3, 45 atm n2, 55 atm h2 (b) 57 atm nh3, 143 atm n2, no h2 (c) 13 atm nh3, 27 atm n2, 82 atm h

According to the balanced equation of this reaction:
N2(g) + 3H2(g) ↔ 2NH3(g)
and when we have Kp = 4.51 x 10^-5 so, in the Kp equation we will substitute by the value of the P for each gas to compare the value with Kp = 4.51x10^-5

a) when we have 98 atm NH3, 45 atm N2, 55 atm H2 by substitution in Kp equation:
Kp= [p(NH3)]^2 / [p(N2)]*[p(H2)]^3 = [98]^2 / [45]*[55]^3
                                                        = 1.28x10^-3 
So here the value is higher than the value of the given Kp.
so the reaction will go leftwards toward the reactants ( to reduce the value of Kp) to reach the equilibrium. 
b) When 57 atm NH3, 143 atm N2, No H2 so like a) by substitution:
Kp = [57]^2 / [143] = 22.7
So the reaction will go leftwards toward the reactants to reduce the value of Kp to reach equilibrium.
c) when 13 atm NH3, 27 atm N2, 82 H2
Kp = [13]^2 / [27]*[82]^3 = 1.135 x 10^-5 So this value is lower than the Kp which is given.
 so, the reaction will go towards the right toward the products to increase the value of Kp to reach the equilibrium.  

They are all decomposition reactions.

Abbreviated as mg-25.