Stoichiometry

StoichiometryStoichiometry

Chapter 9Chapter 9


Def: Def: study of mass relationships in study of mass relationships in chemical reactionschemical reactions

1.1. Mole conversionsMole conversions

2.2. Relationship between products and Relationship between products and reactantsreactants


Revolve around Revolve around balancedbalanced equations:equations:

Coefficients = # particlesCoefficients = # particles

# of # of MOLESMOLES of of particlesparticles

2H2H22 + O + O22 2H 2H22OO

2 moles H2 moles H22 + 1 mole O + 1 mole O2 2 2 moles H 2 moles H22O O


MOLAR RATIOS!!MOLAR RATIOS!! 2H2H22 + O + O22 2H 2H22OO Molar ratio of: Molar ratio of:

HH2 2 : O: O22?? HH22 : H : H22OO OO22 : H : H22OO

Use these as Use these as conversion factorsconversion factors!!

Mole-Mole ProblemsMole-Mole Problems

2H2H22 + O + O22 2H 2H22OO How many moles of HHow many moles of H22 are required are required

to react with 2.5 mole Oto react with 2.5 mole O22??

How many moles of Al(NOHow many moles of Al(NO33))33 are are produced when .75 mol AgNOproduced when .75 mol AgNO33 reacts reacts with Al?with Al?

Mass-Mole ProblemsMass-Mole Problems

FeFe22OO33 + Al + Al Al Al22OO33 + Fe + Fe How many moles of Fe are produced How many moles of Fe are produced

when 5.50 g of Fewhen 5.50 g of Fe22OO33 reacts? reacts? How many moles of water are How many moles of water are

required to react with .25 g of Na?required to react with .25 g of Na?

Mole-Mass ProblemsMole-Mass Problems

Mg + OMg + O22 MgO MgO How many grams of MgO can be How many grams of MgO can be

produced from 2.95 mol Mg reacting produced from 2.95 mol Mg reacting with oxygen?with oxygen?

FF22 + KBr + KBr KF + Br KF + Br22

What mass of KBr is needed to react What mass of KBr is needed to react with 0.96 mol Fwith 0.96 mol F22??

Mass-Mass ProblemsMass-Mass Problems

Sodium phosphate reacts with Sodium phosphate reacts with magnesium nitrate magnesium nitrate

If you have 3.12g of magnesium If you have 3.12g of magnesium nitrate, how many grams of nitrate, how many grams of magnesium phosphate will you magnesium phosphate will you produce?produce?

Helpful SitesHelpful Sites

Mole - MoleMole - Mole http://science.widener.edu/svb/http://science.widener.edu/svb/

tutorial/rxnsmolestomolescsn7.htmltutorial/rxnsmolestomolescsn7.html Mass - MassMass - Mass http://science.widener.edu/svb/http://science.widener.edu/svb/

tutorial/rxnsgramstogramscsn7.htmltutorial/rxnsgramstogramscsn7.html

Limiting ReactantsLimiting Reactants


Amount of products depends on Amount of products depends on amount of reactantsamount of reactants

Car runs because gas reacts with OCar runs because gas reacts with O22

Out of gas = car doesn’t runOut of gas = car doesn’t run Gas = limiting reactantGas = limiting reactant


Limiting reactantLimiting reactant – reactant that – reactant that limits the amount of productlimits the amount of product

Amount of product will ONLY be Amount of product will ONLY be amount made from limiting reactantamount made from limiting reactant

Excess reactantExcess reactant – reactant that is – reactant that is not used up completelynot used up completely

Finding the Limiting ReactantFinding the Limiting Reactant

1.1. Balance the equationBalance the equation

2.2. Pick Pick 1 product1 product and calculate the and calculate the amountamount of product produced from of product produced from both reactantsboth reactants

3.3. Reactant that produced the Reactant that produced the smallest amount of product is smallest amount of product is limiting reactantlimiting reactant

More about Limiting ReactantsMore about Limiting Reactants

Fe + S Fe + S FeS FeS 650. g Fe reacts with 650. g S, what 650. g Fe reacts with 650. g S, what

is the LR?is the LR? What is the mass of sulfur in excess?What is the mass of sulfur in excess? http://www.chemcollective.org/applethttp://www.chemcollective.org/applet

s/stoich.phps/stoich.php

Finding the Limiting ReactantFinding the Limiting Reactant

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

If 3.1 mol Cu and 3.1 mol AgNOIf 3.1 mol Cu and 3.1 mol AgNO33 react, what is the limiting reactant?react, what is the limiting reactant?

How many grams of Ag will be How many grams of Ag will be produced? produced?

Mass excess reactant unreacted?Mass excess reactant unreacted?

Percent YieldPercent Yield

Amount you calculate isn’t what you Amount you calculate isn’t what you always producealways produce

Lab errorsLab errors Theoretical YieldTheoretical Yield – amount – amount

produced based on calculationsproduced based on calculations


Actual YieldActual Yield – amount of product – amount of product “actually” obtained from lab“actually” obtained from lab

Percent YieldPercent Yield – percent of product – percent of product you actually recovered in labyou actually recovered in lab


% Yield = % Yield = actual yieldactual yield x 100 x 100

theoretical yieldtheoretical yield


Pb(NOPb(NO33))22 + KI + KI PbI PbI22 + KNO + KNO33

Determine the % yield if 16.4 g Determine the % yield if 16.4 g Pb(NOPb(NO33))22 reacts with 28.5 g KI if reacts with 28.5 g KI if 18.3g PbI18.3g PbI22 is produced. is produced.

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Stoichiometry