Find the equilibrium concentration

[jumbogala]

Homework Statement

At 300 K, kp = 1.5 x 10¹⁸ for the reaction 3NO --> N₂O + NO₂

If 0.030 mol of NO were placed in a 1.00 L vessel and and equilibrium was established, find the equilibrium concentrations of NO, N₂O and NO₂.

Homework Equations

The Attempt at a Solution

First, I converted kp to kc using the formula kc = kp (RT)^{(change in mols of gas)}

I get kc = (1.5 x 10^18)((0.0821)(300K))^(-1) = 6.08 x 10^16

Then, using an ICE chart, I found the mass action expression is equal to:

x² / (0.030 - 3x)³

kc should be equal to the mass action expression.

But I can't figure out how to solve for x. There don't seem to be any simplifications I can make.

 

[Borek]

There don't seem to be any simplifications I can make.

Looks to me like equilibrium is shifted faaaar to the right. What does it tell you about amount of products?

 

[jumbogala]

That the amount of products is very big compared to the amount of reactants. The reaction goes pretty much to completion.

So, I shouldn't even do an ICE chart, I should just use stoich?

At what point is kc big enough that I can assume the reaction goes to completion?