Limiting reagent [ENDORSED]

[Cyianna 2F]

I'm still confused as to how to determine which molecule is the limiting reagent. How do I find the ratio in order to determine which molecule would be the limiting reagent?

[Chem_Mod]

The procedure for finding limited reagent involves assuming one of the two reagents is in excess (unlimited amount) and the other is as stated in the problem description. You then use stoichiometry to find how many moles of product you would form for each of the situations, where one reagent is unlimited and the other is as described, and vice versa. The one that forms the smaller number of moles of product is the limiting reagent.

The ratio you are describing is the ratio of product to reactant moles read from the balanced chemical equation.

[Ishan Saha 1L]

Another way you can find the limiting reactant is by converting the masses of each reactant to moles and than comparing that molar ratio to that which is described by the balanced equation. For example if the left side of an equation was 2Cl + 4H and once converting the mass of each reactant to moles, there are 3 moles of Cl and 5 moles of H, then the limiting reactant would be Hydrogen. This is because the ratio of Cl:H should be 2:4 according to the equation, but the molar ratio we get is 3:5 instead of 3:6 (equivalent to 2:4). This means that H is limiting because there is comparatively less of this than what would be needed to use up all the Cl. Hope this helps!

[Natalie LeRaybaud 1G]

Yes I agree. The best way is to use stoichiometry to find how many moles of a certain product the reaction will yield based off of the initial amount of reactant you are given in the problem. The reactant that yields less moles of product is the limiting reagent.