CHEMICAL CHEMICAL REACTIONS & REACTIONS &

BALANCING BALANCING EQUATIONSEQUATIONS

ChemistryChemistry

LEARNING OBJECTIVESLEARNING OBJECTIVES

TLW use the law of conservation of TLW use the law of conservation of mass to write and balance mass to write and balance chemical equations (TEKS 8.Dchemical equations (TEKS 8.D

TLW balance equations using 4-TLW balance equations using 4-step “T” Chart Process, Drop Down step “T” Chart Process, Drop Down Approach, or other methodApproach, or other method

AGENDAAGENDA

Law of Conservation of MassLaw of Conservation of Mass Cooking with ChemistryCooking with Chemistry – A Recipe for – A Recipe for

Success and Making Good StuffSuccess and Making Good Stuff Chemical Equations & CoefficientsChemical Equations & Coefficients Balancing Act of Reactants and Products – Balancing Act of Reactants and Products –

The 4-Step “T” Chart ProcessThe 4-Step “T” Chart Process Drop Down ApproachDrop Down Approach

Guided PracticeGuided Practice Independent PracticeIndependent Practice Nuts & Bolts LabNuts & Bolts Lab

CONSERVATIONCONSERVATION OF MASS OF MASS

Total MASS of PRODUCTS Total MASS of PRODUCTS EQUALS Total MASS of EQUALS Total MASS of REACTANTSREACTANTS

CONSERVATION OF CONSERVATION OF MASSMASS

Mass of WOOD Mass of WOOD and AIR before and AIR before burning a fireburning a fire

EQUALSEQUALSMass of ASH and Mass of ASH and GASES after GASES after burning a fireburning a fire

COOKING WITH COOKING WITH CHEMISTRYCHEMISTRY

CHEMICAL EQUATIONSCHEMICAL EQUATIONS ARE ARE LIKE RECIPESLIKE RECIPES

They tell you QUANTITIES They tell you QUANTITIES of INGREDIENTS of INGREDIENTS ((REACTANTSREACTANTS) and ) and QUANTITIES of QUANTITIES of PRODUCTSPRODUCTS

Trail MixTrail MixIngredients (Reactants)Ingredients (Reactants) Product Product

1 c. Mixed Dried Fruit1 c. Mixed Dried Fruit - 6 c. Yummy - 6 c. Yummy andand

½ c. Raisins and/or ½ c. Raisins and/or Healthy Snack Healthy Snack

Dried CranberriesDried Cranberries 1 c. Unsalted Nuts1 c. Unsalted Nuts

peanuts, almonds, or walnutspeanuts, almonds, or walnuts 1 c. Shelled Seeds1 c. Shelled Seeds

sunflower, pumpkinsunflower, pumpkin ½ c. M & Ms½ c. M & Ms 1 c. Cheerios1 c. Cheerios 1 c. Pretzels1 c. Pretzels

Comparing Food Recipes to Comparing Food Recipes to Chemical EquationsChemical Equations

How are they similar?How are they similar?

How are they different?How are they different?

Discovery Education Video Discovery Education Video TimeTime

linklink

CHEMICAL EQUATIONSCHEMICAL EQUATIONSNUMBER of REACTANT NUMBER of REACTANT MOLECULES needed to MOLECULES needed to MAKE a CERTAIN NUMBER of MAKE a CERTAIN NUMBER of PRODUCT MOLECULESPRODUCT MOLECULES

2Na + Cl2Na + Cl22 ---- ----> 2NaCl> 2NaCl

BALANCED BALANCED EQUATIONSEQUATIONS

Correct RATIOS of Correct RATIOS of Molecules are shown as Molecules are shown as COEFFICIENTSCOEFFICIENTS in in BALANCED EQUATIONSBALANCED EQUATIONS

22HH22 + O + O22 ---- ----> > 22HH22OO Coefficients must be Coefficients must be whole numberswhole numbers

In CHEMICAL REACTIONS,In CHEMICAL REACTIONS,BONDS BREAK and REFORMBONDS BREAK and REFORM

ATOMS are REARRANGEDATOMS are REARRANGED

REACTANTS CHANGE to FORM NEW REACTANTS CHANGE to FORM NEW PRODUCTS with DIFFERENT PRODUCTS with DIFFERENT PROPERTIESPROPERTIES

Use FORMULAS and Use FORMULAS and SYMBOLS to show SYMBOLS to show REACTIONREACTION

CONSERVATION OF ATOMSCONSERVATION OF ATOMSNumber of each type of Number of each type of atom in REACTANTS and atom in REACTANTS and PRODUCTS MUST PRODUCTS MUST BALANCEBALANCE

CHEMICAL EQUATIONSCHEMICAL EQUATIONS

How to Balance an EquationHow to Balance an EquationA.A. RulesRules to remember to remember

1. You can 1. You can not changenot change the the chemical chemical formula: formula:

NaCl must stay NaClNaCl must stay NaCl

2. You must leave 2. You must leave subscriptssubscripts alone:alone:

AlClAlCl33 stays AlCl stays AlCl33

You can NOT change the 3You can NOT change the 3

3. You can only 3. You can only addadd coefficients coefficients

a. a. coefficientscoefficients are numbers are numbers that that go in go in frontfront of the of the chemical chemical formulaformula

b. b. 3 3 FeClFeCl22 + + 22 AlAl

the the 33 and and 22 are coefficients.. are coefficients.. (note - (note - 1 is not written down)1 is not written down)

22 AlClAlCl33 + + 3 3 FeFe

TipsTips Balance most complex compounds or Balance most complex compounds or

metals first (look at charges)metals first (look at charges) Balance non-metals next, except O & Balance non-metals next, except O &

HH Balance O and H lastBalance O and H last Look for polyatomic groupings and Look for polyatomic groupings and

balance those as groupsbalance those as groups The polyatomic group The polyatomic group must be on bothmust be on both

sidessides of equation of equation Examples: NOExamples: NO33, OH, SO, OH, SO44

AlAl22(SO(SO44))33 + Ca + Ca(OH)(OH)22 Al Al(OH)(OH)33 + Ca + CaSOSO44

TipsTips

If you have water (HIf you have water (H22O), you can O), you can rewrite it as H and OH separatelyrewrite it as H and OH separately

You can have an interim step of You can have an interim step of coefficient with decimal…. But must coefficient with decimal…. But must multiply through to get whole multiply through to get whole numbers as final balancing actnumbers as final balancing act

Chemical EquationsChemical Equations

Remember the Criss-Cross Rule when Remember the Criss-Cross Rule when working with compoundsworking with compounds

Balance the charges of ions so Balance the charges of ions so molecule has zero (neutral) chargemolecule has zero (neutral) charge

Begin with the positive one first Begin with the positive one first (Fe(Fe+3+3))

Then bring in negative ion (OThen bring in negative ion (O-2-2)) Criss-cross the numbers Criss-cross the numbers Fe Fe22OO33

Use the criss-cross approach Use the criss-cross approach of balancing chargesof balancing chargesExample:Example:

AlAl22(SO(SO44))33 + + 33Ca(OH)Ca(OH)22 22AlAl(OH)(OH)33 + + 33CaCaSOSO44

Group PracticeGroup Practice

Recognizing How Balanced Equations Recognizing How Balanced Equations LookLook

Recap Rules and TipsRecap Rules and Tips

linklink

Processes to UseProcesses to Use

Some people can see how to balance Some people can see how to balance equationsequations

Other folks have developed methods Other folks have developed methods such as:such as: 4-Step “T” Chart Process4-Step “T” Chart Process Drop Down ApproachDrop Down Approach

Draw T-chart

4. Recount

Drop Down ApproachDrop Down ApproachNN22 + O + O22 NO NO22

Re-write to visually show number of atoms Re-write to visually show number of atoms using symbols in each molecular using symbols in each molecular compoundcompound

NNNN + OO + OO NNOOOO

NNNN OOOO NNOOOO

OOOO NNOOOO

Count rows and you have coefficientsCount rows and you have coefficients

NN22 + 2O + 2O22 2NO 2NO22

Internet Drop Down Approach Game Internet Drop Down Approach Game - Classic Chembalancer - Classic Chembalancer http://funbasedlearning.com/chemistry/http://funbasedlearning.com/chemistry/

chemBalancer/ques1.htmchemBalancer/ques1.htm

Group PracticeGroup Practice

Together let’s work through Guided Together let’s work through Guided Reading and Study Workbook pages Reading and Study Workbook pages 79 & 8079 & 80

More Group PracticeMore Group Practice

PP44 + 5O + 5O22 ___ P ___ P22OO55

4Fe + 3O4Fe + 3O22 ___ Fe ___ Fe22OO33 CSCS22 + 3O + 3O22 ___ CO___ CO22 + ___ SO + ___ SO22

___N___N22OO55 + __ NO + __ NO 4N 4N22 + 9O + 9O22 + NO + NO33

__ KOH + __ HCl __ KOH + __ HCl KCl + H KCl + H22OO

More Fun with Balancing More Fun with Balancing EquationsEquations

Internet GameInternet Game http://education.jlab.org/http://education.jlab.org/

elementbalancing/index.htmlelementbalancing/index.html

Individual PracticeIndividual Practice

Practice SetsPractice Sets Balancing Equations – 2Balancing Equations – 2 Balancing Equations and Identifying Balancing Equations and Identifying

Reactions - 3Reactions - 3 Hard copy of other worksheetsHard copy of other worksheets