Equilibrium Constant Table Method

TheRedDevil18

Hi, I just want someone to explain this table to me please, I am totally confused especially with the Change(mol).
Question below:

mfb

If 1 Mole of NH3 is produced, how many moles of N2 and H2 were used to do that?
Hint: Use the molar ratio.

If you know the initial quantity and the change, you get the quantity at equilibrium.

TheRedDevil18

How?, still a bit confused. Could you show me?

mfb

Is "how" related to the quantity at equilibrium?
This is a simple addition. If you start with X moles and produce Y moles, you have X+Y moles.

Is "how" related to the other part?
Just keep in mind that the total number of atoms (both for N and H) cannot change.

TheRedDevil18

I mean the Change, how do they get the change?

mfb

To produce 2 molecules of NH3, you need 1 molecule of N2 (to have 2 N atoms).
To produce 1 molecule of NH3, you need 1/2 molecule of N2.
To produce 1 mole of NH3 (this is given), you need 1/2 moles of N2.

It is that easy.

TheRedDevil18

Okay I understand it now, mole ratio N2:NH3 1/2*1=0.5 and H2:NH3 3/2*1=1.5, the signs are negative because they are being used up right?

mfb

Correct.

TheRedDevil18

What would happen if the change is negative for NH3, Would it now mean that NH3 is being reversed back into its reactants and the reactants would be positive?

mfb

You would need some initial NH3 for that.
In that case: Right.

TheRedDevil18

Okay I think thats it, Thanks for your help