# I need help ( not homework)

1. Jun 17, 2009

### Maroc

I just want a better understanding on what is limitant reactants are and how you go upon getting them?

if this is consider a hmwk problem please move it

2. Jun 17, 2009

### bucher

I think you mean "limiting" reactants. Anyways, limiting reactants are the reactants that you would run out of first during the reaction. They depend both on the stoichiometry and how much you initially start with. You can manage which reactant is limiting by using excess of the other reactants. To not have any excess, then use the stoichiometric amount of each reactant.

3. Jun 17, 2009

### Maroc

thanks!

4. Jun 18, 2009

5. Jul 2, 2009

### rutuj

in chemistry, the limiting reagent, also known as the "limiting reactant", is the chemical that determines how far the reaction will go before the chemical in question gets "used up", causing the reaction to stop. The chemical of which there are fewer moles than the proportion requires is the limiting reagent
Consider a typical thermite reaction:

If 20.0 g of Fe2O3 are reacted with 8.00 g Al(s) in the thermite reaction, Which reactant is limiting?.

First, determine how many moles of Fe(l) can be produced from either reactant.

Moles produced of Fe from reactant Fe2O3

Moles produced of Fe from reactant Al

Because the moles Fe produced from Fe2O3(0.254mol) is less than the moles Fe produced from Al(0.297mol), Fe2O3 is the limiting reagent.

By looking at chemical equation for the thermite reaction, the limiting reagent can be found based on the ratio of moles of one reactant to another and the total atomic mass of the reactant compounds.

Limiting reagent formula
There is a much simpler formula which can be used. However, you must first calculate the moles of both of the reagents in the reaction. Once the number of moles have been figured out, just simply fill in this equation (reagent 1 being the first reactant and 2 being the second):

When the answer to the formula is less than zero, reagent 1 is the excess reagent. When the answer is larger than zero, reagent 1 is the limiting reagent. The number shows how much in excess one reagent is from another. If the answer for the formula is zero, both reagents are perfectly balanced. The unit of an answer is in moles.