Limiting ReactantsLimiting Reactants

Section 12.3Section 12.3

Limiting ReactantsLimiting Reactants

Rarely are the reactants in a chemical equation present in the exact ratios specified by the balanced equation. Generally, there is too much of one and not enough of the other. The chemical reaction will stop once one of the reactants is used up. This leaves the remainder of the reactant that was in excess unreacted. The chemical that you ran out of was the limiting reactant.

Limiting Factor Limiting Factor NotesheetNotesheet

Consider the following recipe:

3 cups flour + 2 eggs + 1 cup sugar + 2 tsp baking powder 12 muffins

A quick check of the pantry shows that the following quantities are available. How many muffins could be made with respect to each ingredient?

9 cups of flour could make ___36___ muffins4 eggs could make __24__ muffins8 cups of sugar could make __96___ muffins10 tsp baking powder could make __60___ muffins

Limiting Factor Note Limiting Factor Note sheetsheet

3 cups flour + 2 eggs + 1 cup sugar + 2 tsp baking powder 12 muffins

What is the maximum number of muffins that could be made considering ALL ingredients? __24___

Which ingredient would you run out of first? _eggs____This ingredient would be referred to as the __limiting_ __reactant____.The other ingredients are said to be __in __ excess .When you run out of an ingredient, you stop producing the _product__.

Limiting Factor Note Limiting Factor Note sheetsheetcont’d…cont’d…Consider the following “recipe” (equation):Consider the following “recipe” (equation):

2 mol of Al + 3 mol of Cl2 mol of Al + 3 mol of Cl22 2 mol of AlCl 2 mol of AlCl33

A quick check of the chemistry lab shows that A quick check of the chemistry lab shows that the following quantities are available. How the following quantities are available. How much product could be made from each? much product could be made from each? (How many times could you make the (How many times could you make the recipe?)recipe?)

10 moles Al ______10 moles Al ______

12 moles Cl12 moles Cl22 _____ _____

What is the maximum amount of AlClWhat is the maximum amount of AlCl33 that could be made that could be made considering all the ingredients? ________considering all the ingredients? ________

We would say the aluminum is _________________ and the We would say the aluminum is _________________ and the chlorine is _________________.chlorine is _________________.

What if you were presented with grams of each reactant? What if you were presented with grams of each reactant? Let’s say there are 100 g of Al and 125 g of ClLet’s say there are 100 g of Al and 125 g of Cl22 available. available. How much product could be formed? (Remember, the How much product could be formed? (Remember, the coefficients in the equation are mole numbers)coefficients in the equation are mole numbers)

100 g of Al would yield ________ mol of product.100 g of Al would yield ________ mol of product.125 g of Cl125 g of Cl22 would yield ________ mol of product. would yield ________ mol of product. How much product could be made considering both How much product could be made considering both

reactants? ________reactants? ________

The limiting factor would be ________.The limiting factor would be ________.

Calculating the Product Calculating the Product when the Reactant is when the Reactant is LimitedLimitedIn the following equation:

If 200 g of sulfur reacts with 100 g of chlorine what mass of sulfur chloride will be produced?

200 100 x

S8 + 4 Cl2 4S2Cl2

256 280 536

Sulfur Chlorine

200 g = x g 100 g = x g256 g 536 g 280 g 536 g

256x = 107200 280x = 53600 x = 418.75 g x = 191.42 g lowest #

Steps for Calculating Steps for Calculating Limiting ReactantsLimiting Reactants

Balance the equationBalance the equation Find the mass of each of the compounds Find the mass of each of the compounds

(molar mass x’s coefficient)(molar mass x’s coefficient) Set up ratios for each of the reactants Set up ratios for each of the reactants

and solveand solve Look for the lowest number – this is your Look for the lowest number – this is your

limiting reactantlimiting reactant

Limiting Reactant Practice ILimiting Reactant Practice IBalance the following formula:

N2 + H2 NH3

1. If you had 112 grams of nitrogen, what is the maximum number of grams of NH3 that could be produced?

2. If you had 18 grams of hydrogen, what is the maximum number of grams of NH3 that could be produced?

3. What is the maximum number of grams of NH3 that can be produced with 112 grams of nitrogen and 18 grams of hydrogen?

5. What is the limiting reactant?

To Determine How Much More of the To Determine How Much More of the Limiting Reactant is Needed to Use Up Limiting Reactant is Needed to Use Up the Excess Reactant and Finish the the Excess Reactant and Finish the Reaction:Reaction:

200 100 S8 + 4 Cl2 4 S2Cl2

256 280

200 g = __x__256 g 280 g

256x = 56000 x = 218.75 g - 100 g = 118.75 g total needed already used additional needed to complete reaction