[briteyellowness]

In the reaction
N2 + 3H2   yields 2NH3

If I start with a reaction chamber of 20 L with 6 atm of hydrogen gas and 6 atm of nitrogen gas.  I then will go to equilibrium with 2 atm of ammonia gas.
What is the total pressure at equilibrium?

The solution turns out to be 10 atm.  

I was just wondering how this can be the answer and yet still violate dalton’s partial pressure law.

Partial Pressure (NH3) = X (mole fraction) * Total Pressure

But if I substitute in 2 = X * 10, I get X = 1/5, whereas in the equation, X = 1/3.  Why is there a discrepancy?

[Donaldson Tan]

the stoichiometric ratio tells u how much nitrogen and hydrogen are CONSUMED
 to produce the equilibrium quantity of ammonia from scratch.