What is a limiting reagent?

Question

Peyton Adams · Accepted Answer

The reactant which runs out first.

One reactant that "limits" the reaction is the limiting reagent; all other reactants are in "excess" until it runs out, at which point the reactant cannot continue. The limiting reagent always comes first in calculations to determine how much product can be produced because it sets the maximum amount that can be produced. I found the following analogy to be helpful: let's say we are making sandwiches, and we need two slices of bread, three tablespoons of peanut butter, and one tablespoon of jam for each sandwich. We can make sandwiches without any leftover "reactants" if we have the ingredients in that exact ratio. Let's say we have four slices of bread. In this scenario, the bread would be the limiting reagent; you could have all the peanut butter and jam in the world, but you could only make two sandwiches. The limiting reagent is determined by mole ratios from the balanced reaction equation and is not always the one with the least amount (in grams or liters). Note: The term "limiting reactant" can also be used to refer to the limiting reagent.

Wyatt Atkins · Answer

A limiting reagent is a reactant in a chemical process which will dictate how much of the products can be formed.

Here is a video which uses the analogy of making sandwiches to explain this concept. The video uses a cool simulation from PhET.

Here is a video that describes this concept in greater detail.

videos from: Noel Pauller

Noah Aldrich · Answer

The #"limiting reagent"# is the reagent in deficiency in a chemical reaction.

Think of a methane combustion reaction, for example: #CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(g)# Since there is little methane in your gas bottle and a lot of oxygen in the atmosphere, it is obvious that methane is the limiting reagent in this situation. Finding the limiting reagent is a necessary step in many problems. If you have a stoichiometric equation, this is usually an easy task.

Wyatt Adkins · Answer

undefined A limiting reagent is a reactant in a chemical reaction that is completely consumed, limiting the amount of product that can be formed. It determines the maximum amount of product that can be produced in the reaction.