Unit 6 Chemical Reactions General Chemistry Spring 2010

Unit 6Unit 6Chemical ReactionsChemical Reactions

General ChemistrySpring 2010

NOMENCLATURE NOMENCLATURE REVIEWREVIEW

Section 1

IonicIonicBasic Rules

◦These have a cation (+) and an anion (-)◦Usually a metal and a nonmetal◦Sometimes contain polyatomic ion(s)

(back of PT)

◦Pay attention to charges Overall charge on ENTIRE formula has to be

ZERO Use subscripts to add charge to make zero Criss-cross is a shortcut but be careful!

◦Practice this on the next slide

Basic Ionic FormulaBasic Ionic Formula Give the formulas for the following

compounds w/o PAI

◦ Potassium sulfide

◦ Magnesium oxide Give the formulas w/ PAI

◦ (DON’T CHANGE THE FORMULA)

◦ Aluminum nitrate

◦ Calcium phosphate

Transition MetalsTransition MetalsIn the name, charge on TM is in ()

◦Ex) Iron (III) chloride

◦Ex) Tin (II) fluoride Use that charge to do criss-cross

To figure out the TM charge do reverse criss-cross. The charge is on ONE TM!

◦Ex) CuO

◦Ex) Cu2O

Covalent NomenclatureCovalent Nomenclature NO CRISS CROSS!!! NO REDUCE!!! The subscript after the symbol = the prefix in

the name The prefix in the name = the subscript in the

formula (what are these rules?)

1. Ex) NO2

2. Ex) N2O

3. Ex) Sulfur hexafluoride

4. Ex) Triphosphorus pentachloride

Diatomic molecules

AcidsAcidsEvery acid formula begins with hydrogenThe other half is either a halogen or a

polyatomic ion◦ Halogen? Use “hydro” in name

Ex) HCl

Ex) HF

◦ Polyatomic? Change ending to “-ic” (for this class)

Ex) H3PO4

Ex) H2SO4

# of H’s is the charge on the PAI

Section 2Section 2Counting Atoms Review

SubscriptSubscriptIndicates the number present Only applies to the element it’s

withAlCl3

◦One aluminum and three chlorines

SubscriptsSubscriptsWhen an element has no

subscript◦The implied subscript is ONE

◦Ag1 = Ag

CoefficientCoefficientAffects anything behind itMultiply everything by the

coefficient3 AlCl3

◦Three aluminums and nine chlorines

Section 3Section 3Reaction Basics

Chemical EquationsChemical EquationsThe “sentences” of chemistryShow how elements react with each other

and what compounds they will form

So that’s what happens when

sodium and water mix!!!!

Parts of a chemical Parts of a chemical EquationEquationReactants

◦Always on the left of the equation◦What the reaction STARTS with

Products◦Always on the right of the equation◦What is produced from the reaction

(made)Yield

◦Arrow◦Where the reaction actually occurs

Can you show me what you just said???

Mg + O2 MgO

Reactants Products

Yield Sign

Symbols in Equations (Table Symbols in Equations (Table 11.1)11.1)

Symbol Explanation

+ Used to separate 2 reactions or 2 products

“Yields,” separates reactions from products

Used in place of for reversible rxns

(s) Designates a R or P in the solid state; placed after the formula

(l) A R or P in the liquid state; placed after formula

(g) “ ” in the gas state; “ ”

(aq) Designates an aqueous solution; the substance is dissolved in water; placed after formula

heat Indicates that head is supplied to the rxn

PtA formula written above the yield sign indicates its use as a catalyst (in this example, platinum)

Section 4Section 4Inventory Reactions

Law of Conservation of Law of Conservation of MassMassThe reason we balance reactionsMatter is neither created nor

destroyed◦Must account for all elements

Before and after reaction

Antoine-Laurent de Lavoisier

was the first to state this law.

Reaction AnatomyReaction Anatomy

KClO3 KCl + O2

K 1

Cl 1

O 3

K 1

Cl 1

O 2

Reactant(s) Products

InventoryInventoryCompare the number of each atom in the

reactants to the products◦ If equal = “balanced reaction”

Abides by the law of conservation of mass◦ If not equal = “not balanced”

Does not abide by the law of conservation of mass; MUST BALANCE

KClO3 KCl + O2

K 1

Cl 1

O 3

K 1

Cl 1

O 2

“Not balanced”

Reactant(s) Products

Section 5Section 5Balancing Reactions

BalanceBalance

1. Inventory first2. Locate one element that does not balance3. Add a coefficient to make it balance

◦ NEVER TOUCH A SUBSCRIPT◦ Look to make odd numbers even

4. Re inventory5. Repeat until balanced

KClO3 KCl + O2

K 1

Cl 1

O 3

K 1

Cl 1

O 2

2

2

2

6

32

2

2

6

balanced

It’s best to leave H and O for the end

BalancingBalancingWhen balancing a chemical

equation you may only change the coefficient (big number in front of the substance)

Balancing example #1:◦ Mg(s) + O2(g) MgO(s)

1 Mg 12 O 1

2 2

2 / / 2 / 2

Balance Combustion = 2 Balance Combustion = 2 CHORCHOR

Combustion is any reaction with CO2 + H2O for products2…coefficient of 2 in front of big hydrocarbonC…balance carbonsH…balance hydrogenO…balance oxygenR…reduce if possible (divide by a common factor, like 2)

C7H16 + O2 CO2 + H2O 2 14 16 22 1 11 7 8

H C

Balancing (cont.)Balancing (cont.)

When balancing a chemical equation you may only change the coefficient (big number in front of the substance)

Balancing example #3:◦ NaOH(aq) + H2SO4(aq) Na2SO4(aq) +

HOH(l)

1 Na 21 OH 12 H 11 SO4 1

22

/ 2 / 2

2 / 2 / Count

polyatomic ions as one

piece!

Practice Problem #1Practice Problem #1

Balance the following reactions:◦ P4(s) + O2(aq) P4O10

◦ Zn + HCl ZnCl2 + H2(g)

◦ Mg(s) + O2(g) MgO(s)

◦ KClO3 KCl + O2(g)

5

2

22

2 2 3

Section 6Section 6Reaction Types

Reaction TypesReaction TypesChemical reactions are classified

into 5 different types:◦This makes it easier to see what is

happening in a reaction◦This makes it easier to predict

products in a reaction

Sorting into piles makes it easier to

see the similarities and

differences

Reaction Types (cont.)Reaction Types (cont.)Five reaction types

◦1) Synthesis (Combination)◦2) Decomposition◦3) Single Replacement◦4) Double Replacement◦5) Combustion

Now let’s look at each type individually

Please NotePlease NoteThe following reactions are not

balancedThe examples are only used to

show the type of reaction

Synthesis = S Synthesis = S (Note: The book uses the term “combination;” it’s the (Note: The book uses the term “combination;” it’s the same thingsame thing))

Two or more substances react to form one new compound

Element + element new compoundcompound + compound new

compoundExamples

◦H2 + N2 NH3

◦Mg + O2 MgO (magnesium oxide)

Decomposition = DDecomposition = D

One compound breaks into two or more simpler products

Compound element/compound + element/compound

Examples◦Na2O Na + O2

◦NH4NO3 N2O + H2O Ammonium nitrate, when heated,

explosively breaks down!

Single Replacement = SRSingle Replacement = SRElement + compound new

element + new compoundExamples

◦AlCl3 + O2 Al2O3 + Cl2◦H2(SO4) + K K2(SO4) + H2

◦Br2 + NaI NaBr + I2◦Br2 + NaCl No Reaction

Halogen activity decreases as you go down group

Activity SeriesActivity SeriesWhether one metal

displaces another depends on upon the reactivities of the metals

A reactive metal will replace any metal listed below it on the activity series◦ Ex) iron will displace

copper from a copper compound, but iron does not similarly displace zinc or calcium

Double Replacement = DRDouble Replacement = DRCompound + compound new

compound + new compoundExamples

◦Na2O + MgBr2 NaBr + MgO

◦H(NO3) + Mg(OH)2 H(OH) + Mg(NO3)2

Which switch? Think about Paula Abdul when you rewrite the formulas!

Combustion = CCombustion = C

An element or a compound reacts with oxygen, usually producing heat and light

Always involves oxygen as a reactantReaction with CO2 + H2O for productsExamples

◦C6H12O6 + O2 CO2 + H2O

◦2 C8H18 + 25 O2 16 CO2 + 18 H2O

Visual Review of Types of Visual Review of Types of ReactionsReactions

Single Replacement

Double Replacement

Combustion

Decomposition Synthesis

Section 7Section 7Predicting Products(p.338-339)

Synthesis (cont.)Synthesis (cont.)

Steps to predict products:◦ 1. Combine the two

reactants in one product (switchy switchy

◦ 2. Balance

Steps in the Irish Countryside


Predict the product and balance:◦ Mg(s) + O2(g)

◦ Be(s) + Br2(g)

◦ Cs(s) + S2(g)

MgO(s)

BeBr2(s)

Cs2S(s)

22

4 2

Decomposition (cont.)Decomposition (cont.)

Steps to predict products:◦ 1. Break the one

reactant into two products Don’t forget about

diatomic moleculesH, N, O, F, Cl, Br, I

◦ 2. Balance

Ancient Steps in Cancun, Mexico


Predict the products and balance:◦ MgCl2(s)

◦ FeS(s)

◦ NaI(s)

Mg(s) + Cl2(g)

Fe(s) + S(s)

Na(s) + I2(s)2 2

Single Replacement (cont.)Single Replacement (cont.)

Steps to predict products:◦ 1. Figure out which metal is

going to replace which other metal

◦ 2. Write the products: One metal is now by itself One metal is now part of a

compound (Switchy Switchy)

◦ 3. Balance

Steps to the House of the Ñusta at Machu Picchu


Predict the products and balance:◦ K(s) + MgS(aq)

◦ Ba(s) + Au(C2H3O2)3(aq)

◦ Zn(s) + HCl(aq)

Mg(s) + K2S(aq)

Au(s) + Ba(C2H3O2)2(aq)

H2(s) + ZnCl2(aq)

2

33 2 2

2

Double Replacement (cont.)Double Replacement (cont.)

Steps to predict products:◦ 1. Figure out which

metal is going to trade partners with which other metal

◦ 2. Write the products: One metal is now in a

compound with the other anion (switchy switchy)

One metal is now in a compound with the other anion (switchy switchy)

◦ 3. BalanceSteps on a Sand Dune at the

edge of the Gobi Desert


Predict the products and balance:◦ FeS(s) + HCl(aq)

◦ CaCl2(aq) + H2SO4(aq)

◦ NH4I(aq) + AgNO3(aq)

FeCl2(aq) + H2S(g)

HCl(aq) + CaSO4(s)

NH4NO3(aq) + AgI(s)

2

2

Combustion (cont.)Combustion (cont.)

Steps to predict products:◦ 1. Write CO2 and H2O as

the products◦ 2. Balance…2CHOR

1st balance C 2nd balance H 3rd balance O

Steps to the Lincoln Memorial


Predict the products and balance:◦ C3H8 (g) + O2(g)

◦ C5H12O(s) + O2(g)

◦ C4H10(s) + O2(g)

CO2(g) + H2O(l)

CO2(g) + H2O(l)

CO2(g) + H2O(l)

5 3 4

2 15 10 12

2 13 8 10

Section 8Section 8Reaction Rates and Equilibrium

Energy BasicsEnergy BasicsFor a reaction to proceed…

◦Reactants’ bonds must break◦Bonds must reform to make products

Energy is required to break reactants apart (their bonds)

Reactions either gain or lose energy, they never stay the same

Activation EnergyActivation EnergyBonds must break in order to

reformEnergy required to break bonds

= ACTIVATION ENERGYAll reactions require thisThe activation energy is always

positive

Energy DiagramEnergy DiagramReactants Products

NaBr + Li(OH) LiBr + Na(OH)

Ene

rgy

in K

ilojo

ules

(kJ

)

Time

Ener

gy o

f rea

ctan

ts

Ene

rgy

of p

rodu

cts

Energy DiagramEnergy DiagramReactants Products


Ene

rgy

in K

ilojo

ules

(kJ

)

Time

Reactants

Products

The difference between the energy of reactants and products =

The total heat or energy of the reaction

OR

ΔΔHH (change in heat) (change in heat)

Activation EnergyActivation Energy

Reactants

Products (bonds have reformed)

NaBr + Li(OH)

LiBr + Na(OH)

Na+1

Li+1Br-1

(OH) -1

Bonds are brokenBonds are broken

Take

s Ene

rgy

The energy required to break the reactants’ bonds =

ACTIVATION ENERGYACTIVATION ENERGY

Reactants Products


Activated ComplexActivated ComplexE

nerg

y in

Kilo

joul

es (

kJ)

Time

Na+1

Li+1Br-1

(OH) -1

Bonds are brokenBonds are broken

Reactants Products


Reactants

Products

The point at which all bonds have been broken and products begin to reform =

ACTIVATED COMPLEXACTIVATED COMPLEX

SummarySummaryE

nerg

y in

Kilo

joul

es (

kJ)

Time

Reactants Products


Reactants

Products

Activated Complex

Activation Energy

Total heat of reaction or ΔH

Rates of ReactionRates of ReactionWays to make reactions happen

faster:◦Make chemicals at higher

concentration◦Increase the temperature◦Make the particles smaller◦Add a catalyst

Rates of Reactions (cont.)Rates of Reactions (cont.)Catalysts lower the activation energy

Heats of ReactionHeats of Reaction

Reactions can either…◦Give off heat

Exothermic The energy level at the end of the reaction is

lower than the energy level at the beginning of the reaction

Therefore, the change in heat (∆H) is negative◦Take in heat

Endothermic The energy level at the end of the reaction is

higher than the energy level at the beginning of the reaction

Therefore, the change in heat (∆H) is positive

Feels Hot

Feels Cold

Exothermic Reaction◦ Reaction loses heat◦ ΔH value is always

negative

Endothermic Reaction◦ Reaction gains heat◦ ΔH value is always

positive

energy

time

energy

time

Exo vs Endothermic Reactions

Bond Formation (cont.)Bond Formation (cont.)

Example #1◦ Endo or

exothermic?

◦ Energy of the Activated complex?

◦ ∆H?

Reactants (500 kJ)

Products (200 kJ)

Act. Energy (150 kJ) Exothermic

650 kJ

-300 kJ

Bond Formation (cont.)Bond Formation (cont.)

Example #2◦ Endo or exothermic?

◦ Activation energy?

◦ Energy of products?

Endothermic

750 kJ

600 kJ

Reactants (200 kJ)

∆H (400 kJ)

Activated Complex (950 kJ)

Documents

Unit 6 Chemical Reactions General Chemistry Spring 2010