[trainee]

Confused on limiting reagent conceptually.
Ex.
http://www.csun.edu/~hcchm001/LIMITREG.pdf

equation 3H2 + N2 -> 2NH3
5g of H2 and 5g of N2
Then H2 = 2*1.01 and N2 = 2(14.01) and NH3 = 17.04

Cool.

But it's the next step I'm a bit confused about (finding the limiting reagent). The site described it as finding "g of product produced from each of the given amounts of reactant"
However this doesn't make sense to me. To make the product you needed both H and N yet we're not considering the N at the moment. Is another way to put the above is how much H2 was needed to make the product NH3? 
If not, can someone describe this in simple terms? Another explanation I found was this:
"mole ratio between reactant and product to convert moles reactant to moles product"
And that sort of helped but this concept hasn't solidified and I'd really appreciate another explanation.

[Borek]

Approach that will probably be least confusing is this: calculate how much N will react with H present - do you have enough nitrogen? Calculate how much H will react with N present - do you have enough hydrogen? If the answer to any of these questions is "no" you have found the limiting reagent. Use it to calculate amount of product.

But: technically it is equivalent to calculating mass of product from initial amounts of all substances and choosing the lowest number as the answer. Yes, it doesn't make chemical sense, but it is mathematically equivalent and gives the correct result a bit faster (one calculation step less to do).