Confused about mole ratio being relative or absolute

[Dorslek]

Let's start with a generalized example:

3A + 1B -> 2C

For the mole amount next to each molecule, am I always to consider these as relative to one another or absolute? Most of the videos I have seen are describing the above as "for every 3 moles of A and 1 mole of B you get 2 moles of C". I believed at some point that these numbers were absolute however, after reading up on equilibrium I discovered that I was incorrect.

So for a reaction such as this:

I have a ratio of 2:1:3. If I used up 0.8 moles of the nitrogen, I read that I would use the ratio to discover that I would produce 0.4 moles of nitrogen and 1.2 moles of hydrogen. Would anyone care to explain this to me?

 

[aroc91]

If I used up 0.8 moles of the nitrogen, I read that I would use the ratio to discover that I would produce 0.4 moles of nitrogen and 1.2 moles of hydrogen.

Correct. A molar ratio is just that, a ratio. It's a ratio in the same way that 1:2 is the same as 0.5:1 or 2:4. Just because the reaction says 2NH₃ doesn't mean you have to use 2 moles.

 

[morrobay]

.8NH₃ x 1N₂/2NH₃= .4N₂
.8NH₃ x 3H₂/2NH₃= 1.2H₂