Originally Posted by Cheryl_pink
So does it mean that
2 : 1
50 : 25 ??
Think of it this way:
For the sake of an example, assume that I give you a recipe to bake cakes. You need 2 eggs and 1 teaspoon of sugar to bake 2 cakes.
Now, if I give you x eggs, how many teaspoon of sugar do you need to ensure none of the eggs are wasted?
In chemistry terms, 2NO + O2 = 2NO2
Since you know you have 50 cm^3 of NO, (ie, x eggs), you need 25 cm^3 of O^2 (ie, x/2 sugar). In this case, we say that NO is the limiting reagent and O2 is in excess.
Let's try a different question:
Say I have 30 g of NO and 8 g of O2, which reagent is limiting and which is in excess?
30 g corresponds to 30/(14+16) = 1 mol
We know that 1 mol of NO needs to react with 0.5 mol of O2. Let us check if we have that much O2.
8/(16+16) = 0.25 => so we don't have that much O2. So O2 is the limiting reagent, NO is the one in excess and we have 0.5 mol of NO left after the reaction (assuming the reaction goes to completion)