Concentration at equilibrium?

Question

Consider the reaction at 500.0K N2(g) + 2O2(g)--->2NO2(g), if delta G rxn=102.60 kJ/mol,

a. what is the value of K?

 

b. If the concentration of N2= 1.5 M and O2 =2.55 M, what is the concentration of NO2 at equilibrium?

 

   I just need part B as I figured out part A already.

Answer 1

Since you already have the K from part (a), you can easily solve for [NO2] at equilibrium.  Using an ICE table:

...........N₂(g) + 2O₂(g) ===> 2NO₂(g)

I.........1.5.........2.55..............0......

C.......-x.........-2x.............+2x.......

E.....1.5-x.....2.55-2x..........2x.......

 

K = [NO₂]²/[N₂][O₂]²

K = (2x)² / (1.5-x)(2.55-x)²

Plug in your value of K and solve for x.  Then [NO₂] at equilibrium will be 2x that value.