CHEMICAL CHEMICAL REACTIONSREACTIONS

Chemical ReactionsChemical Reactions A process by which the atoms of one or A process by which the atoms of one or

more substances are rearranged to form more substances are rearranged to form different substances different substances

Indications that a chemical reaction has Indications that a chemical reaction has occurred are: occurred are: Permanent color changePermanent color change Production of a new solid (precipitate)Production of a new solid (precipitate) Production of a new gasProduction of a new gas Release of heat, light or sparksRelease of heat, light or sparks

Word & Skeleton EquationsWord & Skeleton Equations WORD EQUATIONS:WORD EQUATIONS:

Use words and statements to indicate the reactants and Use words and statements to indicate the reactants and products of a reaction. products of a reaction.

Example:Example: ironiron(s)(s) + chlorine + chlorine(g)(g) iron(III)chloride iron(III)chloride(s)(s) Read “Solid Iron and chlorine gas react to produce solid iron (III) Read “Solid Iron and chlorine gas react to produce solid iron (III)

chloride” chloride” SKELETON EQUATIONS:SKELETON EQUATIONS:

Uses chemical formulas rather than words to identify the Uses chemical formulas rather than words to identify the reactants and products of a chemical reaction. reactants and products of a chemical reaction.

Example:Example: WORD EQUATION: WORD EQUATION: ironiron(s)(s) + chlorine + chlorine(g)(g) iron (III) chloride iron (III) chloride(s)(s) SKELETON EQUATION: FeSKELETON EQUATION: Fe(s)(s) + Cl + Cl2(g)2(g) FeCl FeCl3(s)3(s)

Chemical EquationChemical Equation Statement that uses chemical formulas to Statement that uses chemical formulas to

show the identities and relative amounts show the identities and relative amounts of the substances involved in a chemical of the substances involved in a chemical reactionreaction Example:Example:

WORD EQUATION: WORD EQUATION: ironiron(s)(s) + chlorine + chlorine(g)(g) iron(III)chloride iron(III)chloride(s)(s)

SKELETON EQUATION: FeSKELETON EQUATION: Fe(s)(s) + Cl + Cl2(g)2(g) FeCl FeCl3(s)3(s)

CHEMICAL EQUATION: CHEMICAL EQUATION: 2Fe2Fe(s)(s) + 3Cl + 3Cl2(g)2(g) 2FeCl 2FeCl3(s)3(s)

2Fe + 3Cl2Fe + 3Cl22 2FeCl 2FeCl33

++

Parts of a ReactionParts of a Reaction ReactantsReactants

The substances that combine together (or The substances that combine together (or react)react)

ProductsProducts The new substances created or produced by The new substances created or produced by

the rearrangement of atoms in the reactantsthe rearrangement of atoms in the reactants

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Parts of a ReactionParts of a Reaction

Symbols to knowSymbols to know (cr) = solid(cr) = solid (g) = gas(g) = gas (l) = liquid(l) = liquid (aq) solid dissolved in water(aq) solid dissolved in water ↓ ↓ = precipitate forms= precipitate forms ↑ ↑ = gas forms= gas forms

SubscriptsSubscripts Number of atomsNumber of atoms

CoefficientsCoefficients Number of molecules of compoundNumber of molecules of compound

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Parts of a ReactionParts of a Reaction

(Yield symbol)(Yield symbol) Reads as“to produce” or “yields”Reads as“to produce” or “yields”

+ (on the reactant side)+ (on the reactant side) Reads as “reacts with”Reads as “reacts with”

+ (on the products side)+ (on the products side) Reads as“and”Reads as“and”

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Types of Chemical ReactionsTypes of Chemical Reactions SynthesisSynthesis

Two or more reactants Two or more reactants combine to form one new combine to form one new productproduct

A + B A + B AB AB

DecompositionDecomposition When one reactant When one reactant

breaks down into two or breaks down into two or more productsmore products

AB AB A + B A + B

++

2Na + Cl2Na + Cl22 2NaCl 2NaCl

2H2H22O O 2H 2H22 + O + O22

+ +

Types of Chemical ReactionsTypes of Chemical Reactions

Single DisplacementSingle Displacement When one ion replaces another of a like When one ion replaces another of a like

chargechargeAB + C AB + C AC + B AC + B

Activity SeriesActivity SeriesLiLiKKCaCaNaNaMgMgAlAlZnZn

++ + +

2Li + 2H2Li + 2H22OO 2LiOH + H 2LiOH + H22

Types of Chemical ReactionsTypes of Chemical Reactions

Double DisplacementDouble Displacement When the positive (+) ion of one compound When the positive (+) ion of one compound

replaces the positive (+) ion of another replaces the positive (+) ion of another compound to form two new compoundscompound to form two new compounds AB + CD AB + CD AD + CB AD + CB

Ca(OH)Ca(OH)22 + 2HCl + 2HCl CaCl CaCl22 + 2H + 2H22OO

++ + +

Types of Chemical ReactionsTypes of Chemical Reactions CombustionCombustion

An element or a compound reacts with An element or a compound reacts with oxygen, often producing energy in the oxygen, often producing energy in the form of heat and light.form of heat and light.Ex. Ex.

CHCH4(g)4(g) + 2O + 2O2(g)2(g) CO CO2(g)2(g) + 2H + 2H22OO(g)(g)

+ + + +

Law of Conservation of Law of Conservation of Mass/MatterMass/Matter CONSERVATION OF MASSCONSERVATION OF MASS

Matter cannot be created nor destroyed… it Matter cannot be created nor destroyed… it can only be rearranged!can only be rearranged!

In reactionsIn reactions The total mass of the reactants must equal the The total mass of the reactants must equal the

total mass of the productstotal mass of the products

Due to the conservation of mass/matter… Due to the conservation of mass/matter… ALL CHEMICAL EQUATIONS ALL CHEMICAL EQUATIONS MUST BE BALANCED!!! MUST BE BALANCED!!!

Balancing ReactionsBalancing Reactions There are 4 rules for balancing chemical There are 4 rules for balancing chemical

equations:equations: Once you have written the chemical Once you have written the chemical

formulas for the compounds you…formulas for the compounds you…

1.1. CANNOT change SUBSCRIPTSCANNOT change SUBSCRIPTS2.2. CAN ONLY change COEFFICIENTSCAN ONLY change COEFFICIENTS3.3. Use the LOWEST RATIOSUse the LOWEST RATIOS4.4. If the same polyatomic ion is on both sides of If the same polyatomic ion is on both sides of

the equation, treat it like you would any other the equation, treat it like you would any other atomatom

Steps for Balancing Chemical Steps for Balancing Chemical ReactionsReactions

1.1. Write the skeleton equationWrite the skeleton equation

2.2. Make a product/reactant chartMake a product/reactant chart-- -- List the atoms on each side individuallyList the atoms on each side individually

-- Using subscripts & coefficients, determine how many -- Using subscripts & coefficients, determine how many of each atom existsof each atom exists

3.3. Balance the equation by changing Balance the equation by changing coefficientscoefficients

4.4. Reduce coefficientsReduce coefficients

EXAMPLES OF BALANCING…EXAMPLES OF BALANCING…

Na + INa + I22 NaI NaI

Na = 1Na = 1

I = 2I = 2Na = 1Na = 1

I = 1I = 1Does not equal, so… you must add coefficients…Does not equal, so… you must add coefficients…

22 22

Na = 1Na = 1

I = 2I = 2Na = 1Na = 1

I = 1I = 1

XX 22 XX 22

XX 22THE EQUATION IS NOW BALANCED!!THE EQUATION IS NOW BALANCED!!

EXAMPLES OF BALANCING…EXAMPLES OF BALANCING…

CHCH44 + O + O22 CO CO22 + H + H22OO

C = 1C = 1H = 4H = 4

C = 1C = 1H = 2H = 2

Does not equal, so… you must add coefficients…Does not equal, so… you must add coefficients…

22 22

THE EQUATION IS NOW BALANCED!!THE EQUATION IS NOW BALANCED!!

O = 2O = 2 O = 3O = 3

C = 1C = 1H = 4H = 4

C = 1C = 1H = 2H = 2

O = 2O = 2 O = 3O = 3XX 44XX 44XX 44

Balancing PracticeBalancing PracticeCaCOCaCO33 CaO + CO CaO + CO22

NN22 + H + H22 NH NH33

CHCH4 4 + Cl+ Cl22 CCl CCl44 + HCl + HCl

NaCl + HNaCl + H22 + O + O22 NaOH + Cl NaOH + Cl2 2 + H + H22

Balancing PracticeBalancing Practice

KClOKClO3 3 KCl + O KCl + O22

FeClFeCl3 3 + NaOH + NaOH Fe(OH) Fe(OH)33 + NaCl + NaCl

AgAg22O O Ag + O Ag + O22

K + MgBrK + MgBr22 KBr + Mg KBr + Mg

Energy in Chemical ReactionsEnergy in Chemical Reactions Endothermic ReactionsEndothermic Reactions

More More energy is absorbedenergy is absorbed to break original bonds to break original bonds than is released when new bonds are formed.than is released when new bonds are formed.

Reaction feels cool.Reaction feels cool.

Exothermic ReactionsExothermic Reactions More More energy is releasedenergy is released when new bonds are formed when new bonds are formed

when old bonds are broken.when old bonds are broken. Reaction feels warm.Reaction feels warm. Most reaction are exothermic reactions.Most reaction are exothermic reactions.

CatalystsCatalysts Substance that lowers the activation energy of a reaction in Substance that lowers the activation energy of a reaction in

order to speed up the reactionorder to speed up the reaction Will NOT be used up in the process, just utilized to speed it upWill NOT be used up in the process, just utilized to speed it up