Chapter 8Chapter 8Chemical ReactionsChemical Reactions

Milbank High SchoolMilbank High School

Section 8.1Section 8.1Describing Chemical ChangeDescribing Chemical Change

OBJECTIVES:OBJECTIVES: Write equations describing chemical Write equations describing chemical

reactions, using appropriate symbolsreactions, using appropriate symbols

Section 8.1Section 8.1Describing Chemical ChangeDescribing Chemical Change

OBJECTIVES:OBJECTIVES: Write balanced chemical equations, Write balanced chemical equations,

when given the names or formulas of when given the names or formulas of the reactants and products in a the reactants and products in a chemical reaction.chemical reaction.

All chemical reactionsAll chemical reactions Have two parts:Have two parts:

ReactantsReactants - the substances you start - the substances you start withwith

ProductsProducts- the substances you end up - the substances you end up withwith

The reactants turn into the The reactants turn into the products.products.

Reactants Reactants Products Products

In a chemical reactionIn a chemical reaction The way atoms are joined is changedThe way atoms are joined is changed Atoms aren’t created of destroyed.Atoms aren’t created of destroyed. Can be described several ways:Can be described several ways:

1. In a 1. In a sentence sentence Copper reacts with chlorine to form copper (II) Copper reacts with chlorine to form copper (II)

chloride.chloride.

2. In a 2. In a word equationword equationCopper + chlorine Copper + chlorine copper (II) chloride copper (II) chloride

Symbols in equations-p.206Symbols in equations-p.206 the arrow separates the reactants the arrow separates the reactants

from the productsfrom the products Read “reacts to form”Read “reacts to form” The plus sign = “and”The plus sign = “and” (s) after the formula = solid(s) after the formula = solid (g) after the formula = gas(g) after the formula = gas (l) after the formula = liquid(l) after the formula = liquid

Symbols used in equationsSymbols used in equations

(aq) after the formula - dissolved in (aq) after the formula - dissolved in water, an aqueous solution.water, an aqueous solution.

used after a product indicates a gas used after a product indicates a gas (same as (g))(same as (g))

used after a product indicates a used after a product indicates a solid (same as (s))solid (same as (s))

Symbols used in equationsSymbols used in equations

indicates a reversible indicates a reversible reaction (more later)reaction (more later)

shows that shows that heat is supplied to the reactionheat is supplied to the reaction

is used to indicate a is used to indicate a catalyst is supplied, in this case, catalyst is supplied, in this case, platinum.platinum.

heat ,

Pt

What is a catalyst?What is a catalyst?

A substance that speeds up a A substance that speeds up a reaction, without being changed or reaction, without being changed or used up by the reaction.used up by the reaction.

Enzymes are biological or protein Enzymes are biological or protein catalysts.catalysts.

Skeleton EquationSkeleton Equation

Uses formulas and symbols to Uses formulas and symbols to describe a reactiondescribe a reaction

doesn’t indicate how many.doesn’t indicate how many. All chemical equations are sentences All chemical equations are sentences

that describe reactions.that describe reactions.

Convert these to equationsConvert these to equations

Solid iron (III) sulfide reacts with gaseous Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.and hydrogen sulfide gas.

Nitric acid dissolved in water reacts with Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid solid sodium carbonate to form liquid water and carbon dioxide gas and sodium water and carbon dioxide gas and sodium nitrate dissolved in water. nitrate dissolved in water.

Now, read these:Now, read these:

Fe(s) + OFe(s) + O22(g) (g) Fe Fe22OO33(s)(s)

Cu(s) + AgNOCu(s) + AgNO33(aq) (aq)

Ag(s) + Cu(NOAg(s) + Cu(NO33))22(aq)(aq)

NONO2 2 (g) N(g) N22(g) + O(g) + O22(g)(g)

Pt

Balancing Chemical Balancing Chemical EquationsEquations

Balanced EquationBalanced Equation

Atoms can’t be created or destroyedAtoms can’t be created or destroyed All the atoms we start with we must All the atoms we start with we must

end up withend up with A balanced equation has the same A balanced equation has the same

number of each element on both number of each element on both sides of the equation.sides of the equation.

C + OC + O22 CO CO22

This equation is already balancedThis equation is already balanced What if it isn’t?What if it isn’t?

C + OO COO

C + OC + O22 CO CO

We need one more oxygen in the products.We need one more oxygen in the products. Can’t change the formula, because it Can’t change the formula, because it

describes what it is (carbon monoxide in this describes what it is (carbon monoxide in this example)example)

C + O COO

Must be used to make another COMust be used to make another CO But where did the other C come But where did the other C come

from?from?

C +O

C

OO

OC

Must have started with two CMust have started with two C

2 C + O2 C + O22 2 CO 2 CO

C

+O

C

OO

OC

C

Rules for balancing:Rules for balancing:

Assemble, write the Assemble, write the correct formulascorrect formulas for all for all the reactants and productsthe reactants and products

Count the number of atoms of each type Count the number of atoms of each type appearing on both sidesappearing on both sides

Balance the elements one at a time by Balance the elements one at a time by adding coefficients (the numbers in front) - adding coefficients (the numbers in front) - save H and O until LAST!save H and O until LAST!

Check to make sure it is balanced.Check to make sure it is balanced.

Never change a subscript to balance an Never change a subscript to balance an equation.equation. If you change the formula you are describing a If you change the formula you are describing a

different reaction.different reaction.

HH22O is a different compound than HO is a different compound than H22OO22

Never put a coefficient in the middle of a Never put a coefficient in the middle of a formulaformula 2 NaCl is okay, Na2Cl is not.2 NaCl is okay, Na2Cl is not.

ExampleExample

H2 + H2OO2

Make a table to keep track of where you are at

Example

H2 + H2OO2

Need twice as much O in the product

R PH

O

2

2

2

1

Example

H2 + H2OO2

Changes the O

R PH

O

2

2

2

1

2

Example

H2 + H2OO2

Also changes the H

R PH

O

2

2

2

1

2

2

Example

H2 + H2OO2

Need twice as much H in the reactant

R PH

O

2

2

2

1

2

2

4

Example

H2 + H2OO2

Recount

R PH

O

2

2

2

1

2

2

4

2

Example

H2 + H2OO2

The equation is balanced, has the same number of each kind of atom on both sides

R PH

O

2

2

2

1

2

2

4

2

4

Example

H2 + H2OO2

This is the answer

R PH

O

2

2

2

1

2

2

4

2

4

Not this

Balancing ExamplesBalancing Examples

__AgNOAgNO33 + _Cu + _Cu _Cu(NO _Cu(NO33))22 + _Ag + _Ag

_Mg + _N_Mg + _N22 _Mg _Mg33NN2 2

_P + _O_P + _O22 _P _P44OO1010

_Na + _H_Na + _H22O O _H _H22 + _NaOH + _NaOH

_CH_CH44 + _O + _O22 _CO _CO22 + _H + _H22OO

Section 8.2Section 8.2Types of Chemical ReactionsTypes of Chemical Reactions

OBJECTIVES:OBJECTIVES: Identify a reaction as combination, Identify a reaction as combination,

decomposition, single-replacement, decomposition, single-replacement, double-replacement, or combustiondouble-replacement, or combustion

Section 8.2Section 8.2Types of Chemical ReactionsTypes of Chemical Reactions

OBJECTIVES:OBJECTIVES: Predict the products of combination, Predict the products of combination,

decomposition, single-replacement, decomposition, single-replacement, double-replacement, and combustion double-replacement, and combustion reactions.reactions.

Types of ReactionsTypes of Reactions

There are millions of reactions.There are millions of reactions. Can’t remember them allCan’t remember them all Fall into several categories.Fall into several categories. We will learn 5 major types.We will learn 5 major types. Will be able to Will be able to predictpredict the products. the products. For some, we will be able to predict For some, we will be able to predict

whether they will happen at all.whether they will happen at all. Will recognize them by the reactantsWill recognize them by the reactants

#1 - Combination Reactions#1 - Combination Reactions

Combine - put togetherCombine - put together 2 substances combine to make one 2 substances combine to make one

compound.compound.

Ca +OCa +O22 CaOCaO

SOSO33 + H + H22O O H H22SOSO44

We can predict the products if they are two We can predict the products if they are two elements.elements.

Mg + NMg + N22

Write and balanceWrite and balance

Ca + ClCa + Cl22

Fe + OFe + O22 iron (II) oxide iron (II) oxide

Al + OAl + O22 Remember that the first step is to Remember that the first step is to

write the correct formulaswrite the correct formulas Then balance by using Then balance by using coefficientscoefficients

onlyonly

#2 - Decomposition Reactions#2 - Decomposition Reactions

decompose = fall apartdecompose = fall apart one reactant falls apart into two or one reactant falls apart into two or

more elements or compounds.more elements or compounds.

NaCl Na + ClNaCl Na + Cl22

CaCOCaCO33 CaO + CO CaO + CO22

Note that energy is usually required Note that energy is usually required to decomposeto decompose

electricity

#2 - Decomposition Reactions#2 - Decomposition Reactions

Can predict the products if it is a Can predict the products if it is a binary compound binary compound

Made up of only two elementsMade up of only two elements Falls apart into its elementsFalls apart into its elements

HH22OO

HgOHgO

electricity

#2 - Decomposition Reactions#2 - Decomposition Reactions

If the compound has more than two If the compound has more than two elements you must be given one of elements you must be given one of the productsthe products

The other product will be from the The other product will be from the missing piecesmissing pieces

NiCONiCO3 3 COCO2 2 + ? + ?

HH22COCO33(aq) (aq) COCO2 2 + ? + ?

#3 - Single Replacement#3 - Single Replacement

One element replaces anotherOne element replaces another Reactants must be an element and a Reactants must be an element and a

compound.compound. Products will be a different element and Products will be a different element and

a different compound.a different compound. Na + KCl Na + KCl K + NaCl K + NaCl FF22 + LiCl + LiCl LiF + Cl LiF + Cl22

#3 Single Replacement#3 Single Replacement

Metals replace other metals (and Metals replace other metals (and hydrogen)hydrogen)

K + AlN K + AlN Zn + HCl Zn + HCl Think of water as HOHThink of water as HOH Metals replace one of the H, combine with Metals replace one of the H, combine with

hydroxide.hydroxide. Na + HOH Na + HOH

#3 Single Replacement#3 Single Replacement We can tell We can tell whetherwhether a reaction will happen a reaction will happen Some chemicals are more “Some chemicals are more “active”active” than than

othersothers More active replaces less active More active replaces less active There is a list on page 217 - called the There is a list on page 217 - called the

Activity Series of MetalsActivity Series of Metals Higher on the list replaces lower.Higher on the list replaces lower.

#3 Single Replacement#3 Single Replacement

Note the Note the ** concerning Hydrogen concerning Hydrogen H can be replaced in acids by everything H can be replaced in acids by everything

higherhigher Li, K, Ba, Ca, & Na replace H from acids and Li, K, Ba, Ca, & Na replace H from acids and

waterwater

Fe + CuSOFe + CuSO44

Pb + KCl Pb + KCl Al + HCl Al + HCl

#3 - Single Replacement#3 - Single Replacement What does it mean that Hg and Ag are What does it mean that Hg and Ag are

on the bottom of the list?on the bottom of the list? Nonmetals can replace other nonmetalsNonmetals can replace other nonmetals

Limited to FLimited to F22 , Cl , Cl22 , Br , Br22 , I , I2 2 (halogens) (halogens)

Higher replaces lower.Higher replaces lower.

FF22 + HCl + HCl

BrBr22 + KCl + KCl

#4 - Double Replacement#4 - Double Replacement

Two things replace each other.Two things replace each other. Reactants must be two ionic compounds or Reactants must be two ionic compounds or

acids.acids. Usually in aqueous solutionUsually in aqueous solution

NaOH + NaOH + FeClFeCl33

The positive ions change place.The positive ions change place.

NaOH + NaOH + FeClFeCl33 FeFe+3+3 OHOH-- + Na + Na+1+1 ClCl-1-1

NaOH + NaOH + FeClFeCl33 Fe(Fe(OH)OH)33 + Na + NaClCl

#4 - Double Replacement#4 - Double Replacement

Has certain “driving forces”Has certain “driving forces” Will only happen if one of the products:Will only happen if one of the products: doesn’t dissolve in water and forms a solid (a doesn’t dissolve in water and forms a solid (a

“precipitate”), or “precipitate”), or is a gas that bubbles out, oris a gas that bubbles out, or is a covalent compound (usually is a covalent compound (usually

water).water).

Complete and balanceComplete and balance

assume all of the following reactions assume all of the following reactions take place:take place:CaClCaCl22 + NaOH + NaOH

CuClCuCl22 + K + K22S S

KOH + Fe(NOKOH + Fe(NO33))33

(NH(NH44))22SOSO44 + BaF + BaF22

How to recognize which typeHow to recognize which type

Look at the reactants:Look at the reactants:E + E =E + E = CombinationCombination

CC = = DecompositionDecomposition

E + CE + C = = Single replacementSingle replacement

C + CC + C = = Double replacementDouble replacement

ExamplesExamples

HH22 + O + O22

HH22O O

Zn + HZn + H22SOSO44 HgO HgO

KBr +ClKBr +Cl22

AgNOAgNO33 + NaCl + NaCl

Mg(OH)Mg(OH)22 + H + H22SOSO3 3

#5 - Combustion#5 - Combustion

Means “add oxygen”Means “add oxygen” A compound composed of only C, H, and A compound composed of only C, H, and

maybe O is reacted with oxygenmaybe O is reacted with oxygen If the combustion is complete, the If the combustion is complete, the

products will be COproducts will be CO22 and H and H22O.O.

If the combustion is incomplete, the If the combustion is incomplete, the products will be CO (possibly just C) and products will be CO (possibly just C) and HH22O.O.

ExamplesExamples

CC44HH1010 + O + O22 (assume complete) (assume complete)

CC44HH1010 + O + O22 (incomplete) (incomplete)

CC66HH1212OO66 + O + O22 (complete) (complete)

CC88HH88 +O +O22 (incomplete) (incomplete)

An equation...An equation...

Describes a reactionDescribes a reaction Must be balanced in order to follow the Must be balanced in order to follow the

Law of Conservation of MassLaw of Conservation of Mass Can only be balanced by changing the Can only be balanced by changing the

coefficients.coefficients. Has special symbols to indicate physical Has special symbols to indicate physical

state, and if a catalyst or energy is state, and if a catalyst or energy is required. required.

ReactionsReactions

Come in 5 major types.Come in 5 major types. Can tell what type they are by the Can tell what type they are by the

reactants.reactants. Single ReplacementSingle Replacement happens based on happens based on

the activity seriesthe activity series Double ReplacementDouble Replacement happens if the happens if the

product is a solid, water, or a gas.product is a solid, water, or a gas.

Section 8.3Section 8.3Reactions in Aqueous Reactions in Aqueous

SolutionSolution OBJECTIVES:OBJECTIVES:

Write and balance net ionic equations.Write and balance net ionic equations.

Section 8.3Section 8.3Reactions in Aqueous Reactions in Aqueous

SolutionSolution OBJECTIVES:OBJECTIVES:

Use solubility rules to predict the Use solubility rules to predict the precipitate formed in double-precipitate formed in double-replacement reactions.replacement reactions.

Net Ionic EquationsNet Ionic Equations

Many reactions occur in water- that is, in Many reactions occur in water- that is, in aqueous solutionaqueous solution

Many ionic compounds “dissociate”, or Many ionic compounds “dissociate”, or separate, into cations and anions when separate, into cations and anions when dissolved in waterdissolved in water

Now we can write a Now we can write a complete ionic complete ionic equationequation

Net Ionic EquationsNet Ionic Equations

Example:Example: AgNOAgNO33 + NaCl + NaCl AgCl + NaNO AgCl + NaNO33

1. this is the 1. this is the full equationfull equation

2. now write it as an 2. now write it as an ionic equationionic equation

3. can be simplified by eliminating ions not 3. can be simplified by eliminating ions not directly involved (spectator ions) = directly involved (spectator ions) = net ionic net ionic equationequation

Predicting the PrecipitatePredicting the Precipitate

Insoluble salt = a precipitate - note Insoluble salt = a precipitate - note Figure 8.13, p.227Figure 8.13, p.227

General rules: Table 8.3, p. 227, General rules: Table 8.3, p. 227, Reference p.7 (back of textbook), and in Reference p.7 (back of textbook), and in Lab manual p.338Lab manual p.338

Sample problem 8-11, p.228Sample problem 8-11, p.228