Stoichiometry Mole Ratios Mole Ratios Limiting Reagent Limiting Reagent % Yield % Yield Gas Stoichiometry Gas Stoichiometry.

StoichiometryStoichiometry• Mole RatiosMole Ratios• Limiting ReagentLimiting Reagent• % Yield% Yield• Gas StoichiometryGas Stoichiometry

StoichiometryStoichiometry Chemistry is often called the science of Chemistry is often called the science of

proportions; Kitchen Chemistry/Recipesproportions; Kitchen Chemistry/Recipes StoichiometryStoichiometry : the study of chemical : the study of chemical

quantities based on a quantities based on a balancedbalanced equation. equation.

StoichiometryStoichiometry

Measureable and Quantitative Measureable and Quantitative relationship between relationship between reactantsreactants and and productsproducts

So, a chemical reaction takes place:So, a chemical reaction takes place: Identify:Identify: Classification:Classification: Law of Conservation of Mass:Law of Conservation of Mass:

You Must Remember:You Must Remember:

To To BALANCEBALANCE every equation every equation

Remember the mole??Remember the mole?? Quantities in chemical equations are Quantities in chemical equations are

counted as moles.counted as moles.

http://www.chem.uncc.edu/faculty/murphy/1251/slides/C13/img021.JPG

Chemical RatiosChemical Ratios

Substances in a Substances in a balancedbalanced equation are equation are always in a given proportion to each always in a given proportion to each other.other.

11NN22 + + 33HH22 22NHNH33

The proportions can be written as ratios.The proportions can be written as ratios.

Mole RatiosMole Ratios These proportions are called “mole ratios”.These proportions are called “mole ratios”.

11NN22 + + 33HH22 22NHNH33

For EveryFor Every There There are/isare/is

Creating Creating ratioratio

1N1N22 3H3H221mol N1mol N22/3mol H/3mol H22

1N1N22 2NH2NH33

3H3H22 2NH2NH33

3H3H22 NN22

2NH2NH33 1N1N22

2NH2NH33 3H3H22

Mole RatiosMole Ratios

What is the mole ratio found in the What is the mole ratio found in the balanced equation below?balanced equation below?

NN22OO55 NONO22 + + OO22

The “The “GivenGiven””

If If 2 moles of N2 moles of N22OO55 is reacted, how is reacted, how many moles of NOmany moles of NO22 will be formed? will be formed?

There is always a There is always a givengiven in a in a stoichiometry problem that includes stoichiometry problem that includes

A numeric value (2)A numeric value (2) A metric unit (moles)A metric unit (moles) A substance (NA substance (N22OO55))

Mole-Mole CalculationMole-Mole Calculation

If If 2 moles of N2 moles of N22OO55 is reacted, how is reacted, how many moles of NOmany moles of NO22 will be formed? will be formed?

1) 1) 2 mol N2 mol N22OO55 x mole ratio (which one?) x mole ratio (which one?)

2) 2 mol N2O5 x

mol N2O5 (cancel the given)

3) 2 mol N2O5 x mol NO2 (write what you want)

mol N2O5

Mole-Mole CalculationMole-Mole Calculation

1- Balance the equation

2- Write down your given

3- Use conversion factors to convert moles (use the coefficients here)

We call this the Heart of the equation

Heart of Every EquationHeart of Every Equation

mol unknownmol unknown = =

mol givenmol given

Mole-Mole CalculationsMole-Mole Calculations

______________________________________________

mol mol givengiven

Coef mol

coef mol given

coef mol unknown

Mole-Mass ProblemMole-Mass Problem

How much (mass) B can be formed from a How much (mass) B can be formed from a given number of moles of A? given number of moles of A?

mol Amol A x x mol Bmol B x x g Bg B = g B = g B

mol Amol A 1 mol B 1 mol B

1) The mol-mol ratio comes from the equation1) The mol-mol ratio comes from the equation2) The mol-mass ratio comes from the periodic 2) The mol-mass ratio comes from the periodic

tabletable

CC33HH88 + 5O + 5O22 3CO 3CO22 + 4H + 4H22OO

5.4 moles of propane (C5.4 moles of propane (C33HH88) is ) is converted into how many moles of converted into how many moles of carbon dioxide?carbon dioxide?

Mole-Mass CalculationsMole-Mass Calculations

________________________________________________________________________

mol mol givengiven

coef mol given

coef mol unknownMolar mass (g)

1 mol

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

How many grams of HHow many grams of H22O are O are produced if 1.9 mol of NHproduced if 1.9 mol of NH33 are are combined with excess oxygen?combined with excess oxygen?

Mass-Mole ProblemMass-Mole Problem

How many moles of B can be formed from How many moles of B can be formed from a given mass of A?a given mass of A?

g A x g A x 1 mol A1 mol A x x mol Bmol B x = mol B x = mol B

g Ag A mol Amol A

1) The mol-mol ratio comes from the equation1) The mol-mol ratio comes from the equation2) The mol-mass ratio comes from the periodic 2) The mol-mass ratio comes from the periodic

tabletable

Mass-Mole Calculations:Mass-Mole Calculations:

mol given 1 mol coef mol mol given 1 mol coef mol unknownunknown

____________________________________________________________________

molar mass coef mol molar mass coef mol givengiven

(g)(g)

FeFe22OO33 + 3CO -> 2Fe + 3CO + 3CO -> 2Fe + 3CO22

How many grams of carbon dioxide are How many grams of carbon dioxide are produced with 2 moles of iron (3) produced with 2 moles of iron (3) oxide?oxide?

Mass-Mass ProblemMass-Mass Problem

How much (mass) B can be formed from a How much (mass) B can be formed from a given mass of A?given mass of A?

g A x g A x 1 mol A1 mol A x x mol Bmol B x x g Bg B = g B = g B

g Ag A mol Amol A 1 mol B 1 mol B

1) The mol-mol ratio comes from the equation1) The mol-mol ratio comes from the equation2) The mol-mass ratio comes from the periodic 2) The mol-mass ratio comes from the periodic

tabletable

Mass-Mass Calculations:Mass-Mass Calculations:

g-given 1 mol coef mol molar g-given 1 mol coef mol molar massmass

unknown unknown (g)(g)

________________________________________________________________________ molar mass coef mol 1 molmolar mass coef mol 1 mol

givengiven

FeFe22OO33 + 3CO -> 2Fe + 3CO + 3CO -> 2Fe + 3CO22

How many grams of iron would be How many grams of iron would be produced using 25 grams of iron (3) produced using 25 grams of iron (3) oxide?oxide?

StoichiometryStoichiometry

• Mole RatiosMole Ratios• Limiting Reagent-LRLimiting Reagent-LR• % Yield% Yield• Gas StoichiometryGas Stoichiometry

Limiting ReagentLimiting Reagent

Limiting reagentLimiting reagent = a = a reactantreactant that limits the amount of that limits the amount of productproduct that can be madethat can be made

It can also be thought of as a limiting ingredient

Limiting ReagentLimiting Reagent

RecipeRecipe: peanut butter and jelly : peanut butter and jelly sandwichsandwich

2Br + 3Pb + 2Je 2Br + 3Pb + 2Je 1 Sa 1 Sa 3 ingredients necessary to produce 3 ingredients necessary to produce

one sandwichone sandwich Could any one of these runCould any one of these run

out before the other two?out before the other two?

Excess ReagentsExcess Reagents

ExcessExcess = there’s extra of this = there’s extra of this substancesubstance

*the substance won’t run out*the substance won’t run out

**don’t include this reagent in the don’t include this reagent in the calculationcalculation

If you have 20 loaves of bread, 1 jar If you have 20 loaves of bread, 1 jar of peanut butter and 1 jar of jelly – of peanut butter and 1 jar of jelly – which ingredient is in excess?which ingredient is in excess?

Limiting ReagentLimiting Reagent

To determine the limiting reagent, more To determine the limiting reagent, more than one problem must be donethan one problem must be done

Ex: You have 8 slices of bread and 9 T of Ex: You have 8 slices of bread and 9 T of peanut butter. Which is the limiting peanut butter. Which is the limiting ingredient? (ingredient? (22Br + Br + 33Pb + Pb + 22Je Je 11 Sa) Sa)

8 Br x 8 Br x 1Sa1Sa = 4 Sa = 4 Sa 9 Pb x 9 Pb x 1Sa1Sa = = 3 Sa3 Sa 2 Br2 Br 3Pb 3Pb

Limiting ReagentLimiting Reagent

The reactant that produces the The reactant that produces the smallest amount of productsmallest amount of product is the is the limiting reagent.limiting reagent.

8 Br x 8 Br x 1Sa1Sa = 4 Sa = 4 Sa 9 Pb9 Pb x x 1Sa1Sa = = 3 Sa3 Sa 2 Br2 Br 3Pb 3Pb

Limiting reagent

Smaller quantity

Uses for Limiting ReactantsUses for Limiting Reactants

Nutritional value of food for bodyNutritional value of food for body

Concentration of pollutantsConcentration of pollutants

What to do (write these down):What to do (write these down):

Balance equationBalance equation Convert: 1-Convert: 1-havehave to to molesmoles

2-2-need need toto moles moles

Compare Compare havehave : : needneed One must be > or < One must be > or < ID the LRID the LR Excess Excess compare your compare your havehave : : needneed

Cu + AgNOCu + AgNO33 Cu(NO Cu(NO33))22 + Ag + Ag

Balance firstBalance first Know: Know: you have 3.5 grams of Cu and you have 3.5 grams of Cu and

6 grams of AgNO6 grams of AgNO33. What is the LR . What is the LR and what is excess?and what is excess?

Cu + AgNOCu + AgNO33 Cu(NO Cu(NO33))22 + Ag + Ag

3.5 grams of Cu / 6 grams of AgNO3.5 grams of Cu / 6 grams of AgNO33

Al + OAl + O22 Al Al22OO33

BalanceBalance Known: Known: 0.048 mole of powdered Al 0.048 mole of powdered Al

is placed in a container with 0.030 is placed in a container with 0.030 moles of oxygen. What is the moles of oxygen. What is the limiting reactant?limiting reactant?

Al + OAl + O22 Al Al22OO33

0.048 mole Al / 0.030 moles of 0.048 mole Al / 0.030 moles of oxygenoxygen

StoichiometryStoichiometry

1.1. Ratios and ProportionsRatios and Proportions

2.2. Mole RatiosMole Ratios

3.3. Limiting ReagentLimiting Reagent

4.4. YieldYield

5.5. Gas StoichiometryGas Stoichiometry

% Yield% Yield

Theoretical YieldTheoretical Yield = calculated mass = calculated mass of productof product

Actual YieldActual Yield = mass of product found = mass of product found in labin lab

Percent YieldPercent Yield = = actual yield actual yield x x 100%100%

theoretical yieldtheoretical yield

Percent YieldPercent Yield

Methanol can be produced through Methanol can be produced through the reaction of CO and Hthe reaction of CO and H22 in the in the presence of a catalyst.presence of a catalyst.

CO(CO(gg) + 2H) + 2H22((gg) ) CH CH33OH(OH(ll)) If 75.0 g of CO reacts to produce 68.4 If 75.0 g of CO reacts to produce 68.4

g CHg CH33OH, what is the percent yield of OH, what is the percent yield of CHCH33OH?OH?

79.8%

% Yield% Yield

Chlorobenzene, CChlorobenzene, C66HH55Cl is used in the Cl is used in the production of many important chemicals, production of many important chemicals, such as aspirin, dyes, and disinfectants. such as aspirin, dyes, and disinfectants.

CC66HH66((ll) + Cl) + Cl2(2(gg)) C C66HH55ClCl((ss)) + HCl + HCl((gg))

When 36.8 g of CWhen 36.8 g of C66HH66 react with an react with an excess of Clexcess of Cl22, the actual yield of C, the actual yield of C66HH55Cl is Cl is 38.8 g. What is the percent yield of 38.8 g. What is the percent yield of CC66HH55Cl?Cl?

73.2%

% Yield% Yield

Aluminum reacts with excess copper Aluminum reacts with excess copper (II) sulfate according to the reaction (II) sulfate according to the reaction below. If 1.85 g of Al react and the below. If 1.85 g of Al react and the percent yield of Cu is 56.6%, what percent yield of Cu is 56.6%, what mass of Cu is produced?mass of Cu is produced?

Al(Al(ss) + CuSO) + CuSO44((aqaq) ) Al Al22(SO(SO44))33((aqaq) + ) + Cu(Cu(ss))

3.70 g

StoichiometryStoichiometry

1.1. Ratios and ProportionsRatios and Proportions

2.2. Mole RatiosMole Ratios

3.3. Limiting ReagentLimiting Reagent

4.4. YieldYield

5.5. Gas StoichiometryGas Stoichiometry

Molar VolumeMolar Volume

Molar volume = the Molar volume = the spacespace that that one one molemole of ANY gas fills of ANY gas fills

1 mole = *22.4 liters1 mole = *22.4 litersRemember: 1 L = 1000 mLRemember: 1 L = 1000 mL

*This volume assumes standard *This volume assumes standard temperature and pressure conditionstemperature and pressure conditions

Molar VolumeMolar Volume

1) A quantity of gas has a volume of 1) A quantity of gas has a volume of 124.5 cm124.5 cm33.  How many moles of gas are .  How many moles of gas are there?there?

Molar VolumeMolar Volume

2) Hydrogen sulfide occupies 278.2cm2) Hydrogen sulfide occupies 278.2cm33.  . 

What is the mass of the hydrogen What is the mass of the hydrogen sulfide? sulfide?

Gas StoichiometryGas Stoichiometry

Instead of counting moles in a Instead of counting moles in a reaction, we can also count reaction, we can also count litersliters of a of a gas.gas.

1 liter of N2 reacts with 3 liters of H2 to produce 2 liters of NH3

Gas StoichiometryGas Stoichiometry

What volume of water vapor will be What volume of water vapor will be formed when 8.2 L of Hformed when 8.2 L of H22 reacts with reacts with excess Oexcess O22??

2H2H2 2 ((gg) + O) + O2 2 ((gg) ) 2H 2H22O(O(gg))Use a liter-liter ratio!

Gas StoichiometryGas Stoichiometry

What volume of ammonia will form What volume of ammonia will form when 52.5 g of nitrogen reacts with when 52.5 g of nitrogen reacts with excess hydrogen?excess hydrogen?

gNgN22 mol N mol N22 mol NH mol NH33 L NH L NH33

gNgN22 mol N mol N22 L N L N22 L NH L NH33

Keep digging! No pun intended