Themes > Science > Chemistry > Inorganic Chemistry > Chemical Reaction , Chemical Formulas , Chemical Equation > Chemical Reaction > Determining What Is Reacting > Limiting Reagents

Limiting reagents are the substance that limits the full reaction of all the substances. For example if some one handed you 12 pen caps and 8 pens and asked you to make as many complete pen and cap combinations, how many could be made? Obviously, you can only make eight complete pens and there would be four caps left over so the eight main pen pieces were the limiting reagents in this reaction because there weren't enough pens to allow all the caps to be used up.

For example, if the reaction:

    Ba+2 + F- ==> BaF2
and there are 4 moles of Ba+2 to start and 6 moles of F- to start the reaction. How many moles of BaF2 will be produced?

1. 1st: Balance the reaction.

    Ba+2 + 2F- ==> BaF2

2. 2nd: Divide the number of moles of substance given by the number of moles needed in the reaction.

    4 mol Barium given / 1 mol Barium in equation = 4

    6 mol Fluorine given / 2 mol Fluorine in equation = 3

3. 3rd: Choose the smallest number and this is the limiting reagent.

4. 4th: Multiply the smallest number by the coefficient of the substance that you are looking for:

    3 * 1 (coefficient of BaF2) = 3 mol BaF2 produced


Information provided by : http://library.thinkquest.org