For the iron thiocyanate system, what is the value of the equilibrium constant, Kc, if the following are the concentrations of all species present. Provide your answer to three digits after the decimal. FeSCN2+ 0.501
Fe3+ 0.494
SCN- 0.639

Kc = 0.630

Explanation:

The equilibrium of the thiocyanate system occurs as follows:

FeSCN²⁺(aq) ⇄ Fe³⁺(aq) + SCN⁻(aq)

And equilibrium constant, kc, is:

Kc = [SCN⁻] [Fe³⁺] / [FeSCN²⁺]

Replacing with the gven concentrations:

Kc = 0.639M*0.494M / 0.501M

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.