8.5 Energy8.5 Energy

Focus 1: Living organisms make compounds Focus 1: Living organisms make compounds which are important sources of energywhich are important sources of energy

The sun is the source of The sun is the source of energy on Earthenergy on Earth

SunSun

Autotrophs make their own food by Autotrophs make their own food by photosynthesis. Using chlorophyll, photosynthesis. Using chlorophyll, they convert light energy to they convert light energy to chemical energy.chemical energy.

Light Light energyenergy

PhotosynthesisPhotosynthesis

6CO6CO2(g)2(g) + 6H + 6H22OO(l)(l) C C66HH1212OO6(aq)6(aq) + 6O + 6O2(g)2(g)

This reaction is endothermic, absorbing This reaction is endothermic, absorbing 2830 kJ/mol of glucose formed.2830 kJ/mol of glucose formed.

lightlight

Carbohydrates Carbohydrates CCxx(H(H220)0)yy

Photosynthesis is often written as the production of glucose (CPhotosynthesis is often written as the production of glucose (C66HH1212OO66). ). However, glucose is only one of the many carbohydrates that are made However, glucose is only one of the many carbohydrates that are made by plants.by plants.

Carbohydrates contain the chemical energy that is needed by living things.Carbohydrates contain the chemical energy that is needed by living things.

Common carbohydratesCommon carbohydrates• Glucose and fructose (monosaccharides)Glucose and fructose (monosaccharides)• Sucrose and maltose (disaccharides)Sucrose and maltose (disaccharides)• Starch, cellulose, glycogen (polysaccharides)Starch, cellulose, glycogen (polysaccharides)

Respiration - release of chemical energyRespiration - release of chemical energyCC66HH1212OO66 + O + O22 CO CO22 + H + H22O + energyO + energy

Uses for respiration energyUses for respiration energy• Used directly for activitiesUsed directly for activities• Converted to protein for growth/repair of tissuesConverted to protein for growth/repair of tissues• Stored as fat for energy reservesStored as fat for energy reserves• Most is released as heat back to the environmentMost is released as heat back to the environment

Fossil FuelsFossil Fuels

Decaying plants/animalsDecaying plants/animals COCO22, H, H22O, nutrientsO, nutrients

decomposersdecomposers

Energy releasedEnergy released

Fossil FuelsFossil Fuels•formed when dead and decaying material was buried before complete formed when dead and decaying material was buried before complete decompositiondecomposition•Formed over millions of years due to heat and pressure beneath the Earth’s Formed over millions of years due to heat and pressure beneath the Earth’s surfacesurface•Energy-rich compounds known as Energy-rich compounds known as hydrocarbonshydrocarbons•Chemical potential energy is released when burning in oxygenChemical potential energy is released when burning in oxygen

Question: Where did the chemical potential energy in fossil fuels originate?Question: Where did the chemical potential energy in fossil fuels originate?

Normally when plants and animals die, decomposers (insects, worms and Normally when plants and animals die, decomposers (insects, worms and bacteria) help to break down the decaying material into carbon dioxide, water bacteria) help to break down the decaying material into carbon dioxide, water and other minerals.and other minerals.

Fossil FuelsFossil Fuels• CoalCoal

– Often formed in swamps and mangrovesOften formed in swamps and mangroves– Plant material is anaerobically decomposed (i.e. Plant material is anaerobically decomposed (i.e.

without oxygen) by anaerobic bacteriawithout oxygen) by anaerobic bacteria– As more and more layers of material are deposited, As more and more layers of material are deposited,

carbon content increasescarbon content increases– Temperature and pressure conditions reduce the Temperature and pressure conditions reduce the

amount of oxygen (as COamount of oxygen (as CO22) and hydrogen (as CH) and hydrogen (as CH44))– Some impurities are sulphur and other inorganicsSome impurities are sulphur and other inorganics

• The sequence of production is:The sequence of production is:

BuriedBuried plantplantdebrisdebris

PeatPeat(high H(high H220)0)

BrownBrowncoalcoal

BlackBlackcoalcoal

heatheat heatheat heatheat

pressurepressure pressurepressure pressurepressure

Increasing carbon contentIncreasing carbon content

Fossil FuelsFossil Fuels

• PetroleumPetroleum– Mostly formed from the remains of buried aquatic Mostly formed from the remains of buried aquatic

organisms (e.g. plankton) broken down by anaerobic organisms (e.g. plankton) broken down by anaerobic bacteriabacteria

– They contain a mixture of hydrocarbons commonly They contain a mixture of hydrocarbons commonly known as ‘crude oil’known as ‘crude oil’

– Oil is deposited in porous sedimentary rocks and the Oil is deposited in porous sedimentary rocks and the less dense oil moves upwards unless blocked by less dense oil moves upwards unless blocked by impermeable rockimpermeable rock

– Most of Australia’s oil deposits are found offshore (e.g. Most of Australia’s oil deposits are found offshore (e.g. the Gippsland Basin (Bass Strait) and the North-West the Gippsland Basin (Bass Strait) and the North-West Shelf (WA))Shelf (WA))

Fossil FuelsFossil Fuels

• Natural GasNatural Gas– Mostly the remains of buried aquatic Mostly the remains of buried aquatic

organismsorganisms– Often found in a trapped layer just above Often found in a trapped layer just above

petroleum depositspetroleum deposits– Often contains up to 90% methaneOften contains up to 90% methane

– Also contains propane (CAlso contains propane (C33HH88) and butane ) and butane

(C(C44HH1010) which are liquefied to produce ) which are liquefied to produce LPGLPG

(liquefied petroleum gas)(liquefied petroleum gas)

8.5 Energy8.5 Energy

Focus 2: There is a wide variety of carbon Focus 2: There is a wide variety of carbon compoundscompounds

CarbonCarbon

• Carbon is in Carbon is in Group IVGroup IV of the of the periodic tableperiodic table

• Carbon has Carbon has 4 valence 4 valence electronselectrons

• Carbon can form Carbon can form 4 covalent 4 covalent bondsbonds

• Carbon can form single, double Carbon can form single, double and triple bonds with a wide and triple bonds with a wide variety of elements forming variety of elements forming nearly nearly ten million known ten million known compoundscompounds

1s1s22 2s 2s22 2p 2p22

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Tetravalent CarbonTetravalent Carbon

Because carbon has Because carbon has four valence four valence electronselectrons, it forms four bonds , it forms four bonds with other elements to make up with other elements to make up a full valence shell of 8. All a full valence shell of 8. All valence electrons are involved valence electrons are involved in bonding.in bonding.

This bonding leads to This bonding leads to tetrahedraltetrahedral shapes when all of the bonds shapes when all of the bonds involved are single bonds.involved are single bonds.

Hydrocarbons are made up of Hydrocarbons are made up of carbon bonded to hydrogen, but carbon bonded to hydrogen, but many elements can and do take many elements can and do take the place of hydrogen.the place of hydrogen.

Common elements that bond to Common elements that bond to carbon are carbon are N, O, SN, O, S and the and the halogenshalogens (e.g. Cl, F). (e.g. Cl, F).

Carbon atomCarbon atomHydrogenHydrogenatomsatoms

Methane CHMethane CH44

CarbonCarbon tetrachloridetetrachloride CClCCl44

Carbon atomCarbon atom

ChlorineChlorine atomsatoms

Carbon BondingCarbon Bonding

CC CC

HH

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HH

HH

CC CCHH

HH

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Single bond - ethaneSingle bond - ethane

Triple bond – ethyneTriple bond – ethyne(acetylene)(acetylene)

Double bond - etheneDouble bond - ethene

CC22HH66

CC22HH22

CC22HH44

Structural Structural FormulaFormula

Molecular Molecular FormulaFormula

Forms of Carbon Forms of Carbon Allotropes of carbonAllotropes of carbonAllotropes are forms of an element that have different properties. Carbon Allotropes are forms of an element that have different properties. Carbon

has four:has four:1.1. AmorphousAmorphous – soot from incomplete burning of hydrocarbons – soot from incomplete burning of hydrocarbons

consisting of shapeless particlesconsisting of shapeless particles2.2. GraphiteGraphite – thin sheets of six-sided carbon rings in layers held – thin sheets of six-sided carbon rings in layers held

together by weak intermolecular forcestogether by weak intermolecular forces3.3. DiamondDiamond – crystalline covalent network substance – crystalline covalent network substance4.4. Buckminsterfullerene (‘bucky balls’)Buckminsterfullerene (‘bucky balls’) – contains 60 carbons with 5 – contains 60 carbons with 5

and 6-carbon rings arranged in a structure similar to a soccer ball. and 6-carbon rings arranged in a structure similar to a soccer ball.

http://www.bfi.org/node/351www.teachmetuition.co.uk www.teachmetuition.co.uk

GraphiteGraphite Bucky ballBucky ballDiamondDiamond

Carbon Properties & UsesCarbon Properties & Uses

DiamondDiamond• 3-D network of 3-D network of

tetrahedral shapestetrahedral shapes• Strong covalent bonds Strong covalent bonds

with tightly bound e- with tightly bound e- resulting in an resulting in an extremely hard extremely hard substance (the hardest substance (the hardest known) with high mp/bp.known) with high mp/bp.

UsesUses• Glass cutting Glass cutting • Saw bladesSaw blades• Dentist’s drillsDentist’s drills

GraphiteGraphite• Thin sheets of 6-carbon Thin sheets of 6-carbon

rings rings • Layers are held together Layers are held together

by weak intermolecular by weak intermolecular forces leading to a very forces leading to a very soft substance that easily soft substance that easily turns to a fine slippery turns to a fine slippery powder.powder.

• Graphite also conducts Graphite also conducts electricityelectricity

UsesUses• The “lead” in pencilsThe “lead” in pencils• A solid lubricant such as A solid lubricant such as

in car door catchesin car door catches• Electrodes in batteriesElectrodes in batteries

8.5 Energy8.5 Energy

Focus 3: A variety of carbon compounds are Focus 3: A variety of carbon compounds are extracted from organic sourcesextracted from organic sources

Fractional DistillationFractional Distillation

Recall that crude oil contains Recall that crude oil contains a mixture of hydrocarbons a mixture of hydrocarbons ranging from one carbon ranging from one carbon (C1) up to more than C24.(C1) up to more than C24.

Fractional distillationFractional distillation allows allows for these components or for these components or ‘fractions’ to be separated ‘fractions’ to be separated using a using a fractionating fractionating columncolumn..

In this process, heat is In this process, heat is applied to the bottom of applied to the bottom of the column and lighter the column and lighter compounds with lower compounds with lower boiling points rise to the boiling points rise to the top, while heavier top, while heavier compounds remain compounds remain towards the bottom of the towards the bottom of the column. column.

Source: http://www.bbc.co.uk/schools/gcsebitesize/chemistry/usefulproductsoil/oil_and_oilproductsrev5.shtml

Fractional DistillationFractional Distillation

InvestigationInvestigation

In the laboratory, you will In the laboratory, you will perform a separation perform a separation of ethanol and water of ethanol and water using a fractionating using a fractionating column similar to the column similar to the one on the right.one on the right.

How will you ensure that How will you ensure that the final product is the final product is pure ethanol?pure ethanol?

A fractional distillation setup. A fractional distillation setup.

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Hydrocarbon nomenclatureHydrocarbon nomenclature

AlkanesAlkanes - hydrocarbons that - hydrocarbons that contain only single bonds. The table to contain only single bonds. The table to the right shows the alkane the right shows the alkane homologous homologous series series (a family of compounds that have (a family of compounds that have the same general formula).the same general formula).

Formula Formula – C– CnnHH2n+22n+2

Straight-chain alkanes Straight-chain alkanes – carbons – carbons joined together to form a single chain joined together to form a single chain with no branching.with no branching.

Number of CNumber of C AlkaneAlkane

11 MethaneMethane

22 EthaneEthane

33 PropanePropane

44 ButaneButane

55 PentanePentane

66 HexaneHexane

77 HeptaneHeptane

88 OctaneOctane

Methane Ethane Propane Butane

Structural formulaeStructural formulae

Hydrocarbon nomenclatureHydrocarbon nomenclatureAlkenesAlkenes – hydrocarbons that contain – hydrocarbons that contain

one double bond between two carbon one double bond between two carbon atoms.atoms.

Formula Formula – C– CnnHH2n2n

IsomersIsomers – – compounds that have the compounds that have the same molecular formula, but same molecular formula, but different structuredifferent structure. .

Alkenes have isomers because the Alkenes have isomers because the double bond can be in a different double bond can be in a different location above C4. The location of location above C4. The location of the double bond is indicated by a the double bond is indicated by a numerical prefix counting from the numerical prefix counting from the shortest end.shortest end.

Number of CNumber of C AlkeneAlkene

11 NANA

22 EtheneEthene

33 PropenePropene

44 ButeneButene

55 PentenePentene

66 HexeneHexene

77 HepteneHeptene

88 OcteneOctene

CHCH CHCH33CHCH22CHCH22 CHCH CHCH33CHCH22CHCH22 CHCH22 CHCH CHCH33CHCHCHCH22 CHCH22

1-butene 1-pentene 2-pentene (NOT 3-pentene)

Condensed structural formulaeCondensed structural formulae

Hydrocarbon nomenclatureHydrocarbon nomenclature

AlkynesAlkynes – – hydrocarbons hydrocarbons that contain one triple that contain one triple bond between two carbon bond between two carbon atoms.atoms.

Formula Formula – C– CnnHH2n-22n-2

Number of CNumber of C AlkyneAlkyne

11 NANA

22 EthyneEthyne

33 PropynePropyne

44 ButyneButyne

55 PentynePentyne

66 HexyneHexyne

77 HeptyneHeptyne

88 OctyneOctyne

As with alkenes, a numerical As with alkenes, a numerical prefix indicates the location of prefix indicates the location of the triple bond.the triple bond.

Properties of alkanes/alkenesProperties of alkanes/alkenes

AlkanesAlkanes AlkenesAlkenes

BP/MPBP/MP increase with increased increase with increased number of carbon atoms. C1 to C4 number of carbon atoms. C1 to C4 are gases at room temp. C5 to C17 are gases at room temp. C5 to C17 are liquids. All above C18 are solid.are liquids. All above C18 are solid.

BP/MPBP/MP increase with increased increase with increased number of carbon atoms. C2 to C4 number of carbon atoms. C2 to C4 are gases at room temp. C5 to C15 are gases at room temp. C5 to C15 are liquids. All above C16 are solid.are liquids. All above C16 are solid.

Weak Weak dispersion forcesdispersion forces that increase that increase in strength with increasing molecular in strength with increasing molecular mass. (More emass. (More e-- = stronger forces) = stronger forces)

Similar to alkanes.Similar to alkanes.

Non-polar Non-polar due to symmetrical shape due to symmetrical shape and similarity of electronegativity of H and similarity of electronegativity of H and C.and C.

Similar to alkanes.Similar to alkanes.

Densities Densities increase with increased increase with increased molecular mass. All are less dense molecular mass. All are less dense than water. (e.g. float on top)than water. (e.g. float on top)

Similar to alkanes.Similar to alkanes.

Volatility of hydrocarbonsVolatility of hydrocarbons

Liquid hydrocarbons such as petrol (C5-C12) tend to readily Liquid hydrocarbons such as petrol (C5-C12) tend to readily evaporate. This tendency is known as evaporate. This tendency is known as volatilityvolatility..

In a closed container, a dynamic equilibrium will be achieved In a closed container, a dynamic equilibrium will be achieved between evaporation and condensation (i.e. same rate).between evaporation and condensation (i.e. same rate).

Once dynamic equilibrium is established, a constant pressure Once dynamic equilibrium is established, a constant pressure is exerted on the container known as is exerted on the container known as vapour pressure.vapour pressure.

Volatile compounds have a Volatile compounds have a tendency to move from liquid to tendency to move from liquid to gasgas

VapourVapour

LiquidLiquid

PetrolPetrol

The weaker the The weaker the intermolecular intermolecular forces, the lower the forces, the lower the boiling point and the boiling point and the greater the volatility.greater the volatility.

Safe Storage of alkanesSafe Storage of alkanes

• Minimise the quantity of material to be storedMinimise the quantity of material to be stored• Store in cool place with good ventilation (flammable cabinet)Store in cool place with good ventilation (flammable cabinet)• Avoid inhaling the vapoursAvoid inhaling the vapours• Use in a fume hoodUse in a fume hood• Keep away from sparks or naked flamesKeep away from sparks or naked flames• Store in approved containers (sturdy with narrow neck)Store in approved containers (sturdy with narrow neck)• Gas cylinders should be regularly checked and stored outside, under cover Gas cylinders should be regularly checked and stored outside, under cover

in well-ventilated area. They should also be strapped to a permanent in well-ventilated area. They should also be strapped to a permanent structure.structure.

The weak intermolecular forces in low The weak intermolecular forces in low molecular weight alkanes results in extreme molecular weight alkanes results in extreme flammability. In addition, some alkanes are flammability. In addition, some alkanes are carcinogenic, so safe storage of alkanes (and carcinogenic, so safe storage of alkanes (and many other hydrocarbons) needs to consider many other hydrocarbons) needs to consider the following:the following:

Task: Find specific safety considerations for alkanes C1 to C8. Make aTask: Find specific safety considerations for alkanes C1 to C8. Make asafety poster to put up in a chemical store room.safety poster to put up in a chemical store room.

8.5 Energy8.5 EnergyFocus 4: Combustion provides another opportunity to Focus 4: Combustion provides another opportunity to examine the conditions under which chemical examine the conditions under which chemical reactions occur.reactions occur.

Chemical Reaction IndicatorsChemical Reaction Indicators

• At least one new substance is formed in a chemical reactionAt least one new substance is formed in a chemical reaction• A change in colour (not always a chemical reaction)A change in colour (not always a chemical reaction)• A gas is given off (acid + carbonate produces COA gas is given off (acid + carbonate produces CO22))• Heat is produced or absorbed (combustion)Heat is produced or absorbed (combustion)• Light is given off (chemiluminescence)Light is given off (chemiluminescence)• A precipitate forms (insoluble ionic compounds)A precipitate forms (insoluble ionic compounds)

Acid + CarbonateAcid + Carbonate

Burning magnesiumBurning magnesium

Glow Stick - ChemiluminescenceGlow Stick - Chemiluminescence

Precipitation reactionPrecipitation reaction

Combustion is exothermicCombustion is exothermic

Combustion is the process of burningCombustion is the process of burning

Most often, the combustion of a Most often, the combustion of a material involves its combination material involves its combination with oxygen gas.with oxygen gas.

Because combustion reactions Because combustion reactions release energy in the form of heat release energy in the form of heat and light, they are and light, they are exothermicexothermic..

Fire in the Penola Forest (SA), Ash Wednesday 1983 Fire in the Penola Forest (SA), Ash Wednesday 1983

(Source: (Source: www.austehc.unimelb.edu.au/ fam/1611_image.html))

Example:Example:The combustion of methane The combustion of methane (natural gas) in oxygen:(natural gas) in oxygen:

CHCH44 + 2O + 2O22 CO CO22 + 2H + 2H22OO

∆ ∆ HHrxnrxn = -832 kJ/mol (exothermic) = -832 kJ/mol (exothermic)

Combustion: why exothermic?Combustion: why exothermic?

Recall that:Recall that:• Energy is required to break bondsEnergy is required to break bonds• Energy is released when bonds formEnergy is released when bonds form

In the previous example involving the combustion of methane:In the previous example involving the combustion of methane:

CHCH44 + 2O + 2O22 CO CO22 + 2H + 2H22O + 832kJO + 832kJ

And remembering that:And remembering that:

∆∆ HHrxnrxn = H (products) – H (reactants) = H (products) – H (reactants) oror ∆ ∆ HHrxnrxn = ∑ E (bonds broken) - ∑ E (bonds formed) = ∑ E (bonds broken) - ∑ E (bonds formed)

This reaction releases more energy than it absorbs resulting in a negative value for This reaction releases more energy than it absorbs resulting in a negative value for ∆∆ HrxnHrxn

Breaking bondsBreaking bondsAbsorbs energyAbsorbs energy

Forming bondsForming bondsReleases energyReleases energy

H reactants < H productsH reactants < H products

Energy requiredEnergy requiredto break bondsto break bonds

Energy releasedEnergy releasedwhen bonds formedwhen bonds formed

Bond Bond energy, kJ/mol

C–C 347

C=C 615

C≡C 812

C–O 360

C=O 798

F–F 158

Cl–Cl 244

C–H 414

H–H 436

H–O 464

O=O 498

AVERAGE BOND ENERGIES OF COMMON BONDS AVERAGE BOND ENERGIES OF COMMON BONDS

Use these bond energy values to determine the ∆ Hrxn of methane combustionUse these bond energy values to determine the ∆ Hrxn of methane combustion∆∆ HHrxnrxn = ∑ E (bonds broken) - ∑ E (bonds formed) = ∑ E (bonds broken) - ∑ E (bonds formed)

Combustion of organicsCombustion of organics

Complete combustion

METHANE (LAB GAS): CHMETHANE (LAB GAS): CH4(g)4(g) + 2O + 2O2(g)2(g) CO CO2(g)2(g) + 2H + 2H22OO(g)(g) + 832kJ + 832kJ

PROPANE (LPG): CPROPANE (LPG): C33HH8(g)8(g) + 5O + 5O2(g)2(g) 3CO 3CO2(g)2(g) + 4H + 4H22OO(g)(g) + 1560kJ + 1560kJ

OCTANE (PETROL): COCTANE (PETROL): C88HH18(l)18(l) + 25/2O + 25/2O2(g)2(g) 8CO 8CO2(g)2(g) + 9H + 9H22O O (g)(g) + 5460kJ + 5460kJ

CARBON (COKE): CCARBON (COKE): C(s)(s) + O + O22 CO CO2(g)2(g) + 393kJ + 393kJ

Note that all hydrocarbons produce carbon dioxide (a greenhouse Note that all hydrocarbons produce carbon dioxide (a greenhouse gas) and water. These are the only products when there is gas) and water. These are the only products when there is sufficient oxygen (i.e. complete combustion). sufficient oxygen (i.e. complete combustion).

When the oxygen available is insufficient, incomplete combustion When the oxygen available is insufficient, incomplete combustion results in other pollutants.results in other pollutants.

All exothermicAll exothermic

Combustion of organicsCombustion of organics

Incomplete combustionIncomplete combustion

As the quantity of oxygen decreases, combustion of hydrocarbons becomes As the quantity of oxygen decreases, combustion of hydrocarbons becomes more and more incomplete, leading to the production of the pollutants more and more incomplete, leading to the production of the pollutants carbon monoxide and carbon (soot). Consider the hydrocarbon pentane:carbon monoxide and carbon (soot). Consider the hydrocarbon pentane:

Complete:Complete: CC55HH12(l)12(l) + + 88OO2(g)2(g) 5CO 5CO2(g)2(g) + 6H + 6H22O O (g) (g)

Incomplete (less OIncomplete (less O22):): C C55HH12(l)12(l) + + 66OO2(g)2(g) 4 4COCO(g)(g) + CO + CO2(g)2(g) + 6H + 6H22O O (g) (g)

Incomplete (even less OIncomplete (even less O22): ): CC55HH12(l)12(l) + + 44OO2(g)2(g) 2 2COCO(g)(g) + 3 + 3CC(s)(s) + 6H + 6H22O O (g) (g)

Incomplete combustion productsIncomplete combustion products

Incomplete combustion of hydrocarbons can produce CO and C.Incomplete combustion of hydrocarbons can produce CO and C.

Other Combustion PollutantsOther Combustion Pollutants

Sulfur Dioxide/TrioxideSulfur Dioxide/TrioxideSulfur is an impurity in fossil fuels, mainly coal (up to 5%). Sulfur is an impurity in fossil fuels, mainly coal (up to 5%).

When sulfur burns in air sulfur dioxide is produced:When sulfur burns in air sulfur dioxide is produced:

SS(s)(s) + O + O2(g)2(g) SO SO2(g)2(g)

Sulfur trioxide can be produced by further oxidation of SOSulfur trioxide can be produced by further oxidation of SO22

2SO2SO2(g) 2(g) + O+ O2(g)2(g) 2SO 2SO3(g)3(g)

These two gases can combine with water in the These two gases can combine with water in the atmosphere to produce atmosphere to produce acid rainacid rain::

SOSO2(g)2(g) + H + H22OO(l)(l) H H22SOSO3(aq)3(aq) (sulfurous acid) (sulfurous acid)

SOSO3(g)3(g) + H + H22OO(l) (l) H H22SOSO4(aq)4(aq) (sulfuric acid) (sulfuric acid) www.robl.w1.com www.robl.w1.com

Acid rain effectsAcid rain effects

Other Combustion PollutantsOther Combustion Pollutants

Oxides of NitrogenOxides of Nitrogen (NOx) (NOx)Nitrogen and oxygen in the air can react at high temperatures Nitrogen and oxygen in the air can react at high temperatures

that are present inside car engines:that are present inside car engines:

NN2(g) 2(g) + O+ O2(g)2(g) 2NO 2NO (g) (g)

2NO2NO(g) (g) + O+ O2(g)2(g) 2NO 2NO2(g)2(g)

Nitrogen dioxide produces the brown haze known as Nitrogen dioxide produces the brown haze known as photochemical smogphotochemical smog. This causes respiratory . This causes respiratory problems in many people. problems in many people. In addition, NOIn addition, NO22 can react with UV light to produce toxic can react with UV light to produce toxic

ozone Oozone O33. .

NONO2(g) 2(g) + UV + UV 2NO 2NO2(g) 2(g) + O(g)+ O(g)

OO(g) (g) + O+ O2(g)2(g) O O3(g)3(g)

www.birmingham.gov.uk www.birmingham.gov.uk

Photochemical smogPhotochemical smog

Controlling PollutionControlling Pollution• Use low sulfur coal (Australian coal is relatively Use low sulfur coal (Australian coal is relatively

low in sulfur)low in sulfur)

• Remove sulfur dioxide from effluent gas at power Remove sulfur dioxide from effluent gas at power stations (very expensive)stations (very expensive)

• Keep car engines tuned properly so that Keep car engines tuned properly so that incomplete combustion is minimised.incomplete combustion is minimised.

• Catalytic converters mounted to motor vehicle Catalytic converters mounted to motor vehicle exhaust systems remove unburned hydrocarbons exhaust systems remove unburned hydrocarbons and oxides of nitrogen. and oxides of nitrogen.

2NO2NO(g) (g) + 2CO+ 2CO(g)(g) N N2(g)2(g) + 2CO + 2CO2(g)2(g)

Energy changes in chemical Energy changes in chemical reactionsreactions

Exothermic reactionsExothermic reactions

The enthalpy of the reactants is The enthalpy of the reactants is higher than the products.higher than the products.

ReactantsReactants

ProductsProducts

Endothermic reactionsEndothermic reactions

The enthalpy of the reactants is The enthalpy of the reactants is lower than the products.lower than the products.

ProductsProducts

ReactantsReactants

Enth

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Enth

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∆∆ H is -ve ∆∆ H is +veHeat releasedHeat released Heat absorbedHeat absorbed

Reaction progressionReaction progression Reaction progressionReaction progression

Activation EnergyActivation Energy

Reaction progressReaction progress

ReactantsReactants

ProductsProducts

enth

alp

yen

thal

py

ActivationActivationenergyenergy

∆∆ H

The activation energy is the minimum The activation energy is the minimum amount of energy that is required by the amount of energy that is required by the reactants for the reaction to proceed to reactants for the reaction to proceed to the products.the products.

CatalystsCatalysts

Reaction progressReaction progress

ReactantsReactants

ProductsProducts

enth

alp

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thal

py

ActivationActivationenergyenergy

∆∆ H

A catalyst lowers the activation energy A catalyst lowers the activation energy of a reaction, but does not change the of a reaction, but does not change the overall overall ∆∆ H H of the reaction.of the reaction.

Catalysed path Catalysed path

Lowered activationLowered activationenergyenergy

Ignition TemperatureIgnition Temperature

The minimum temperature required by The minimum temperature required by a substance to ignite.a substance to ignite.

In order for a fuel to ignite, a certain In order for a fuel to ignite, a certain amount of heat energy must be applied to amount of heat energy must be applied to the substance and the air that will be the substance and the air that will be involved in the combustion.involved in the combustion.

Not all of the particles must be heated to Not all of the particles must be heated to this temperature to start the reaction.this temperature to start the reaction.

Once the combustion reaction has started, Once the combustion reaction has started, the resulting release of energy provides the resulting release of energy provides sufficient temperatures for neighbouring sufficient temperatures for neighbouring particles to ignite.particles to ignite.

The higher the activation The higher the activation energy, the higher the energy, the higher the ignition temperatureignition temperature

Friction on the Friction on the match head match head provides enough provides enough energy to ignite energy to ignite the sulfur in the the sulfur in the match.match.

8.5 Energy8.5 EnergyFocus 5: The rate of energy release is Focus 5: The rate of energy release is affected by factors such as types of reactantsaffected by factors such as types of reactants

Particle CollisionsParticle CollisionsFor a reaction to proceed to products, the For a reaction to proceed to products, the

reactants must collide with one reactants must collide with one another.another.

Rate of reactionRate of reactionThe rate of a reaction is the rate that reactants disappear and The rate of a reaction is the rate that reactants disappear and products form. As the reaction proceeds and reactants are used products form. As the reaction proceeds and reactants are used up, the rate decreases. Since the reacting particles must collide up, the rate decreases. Since the reacting particles must collide to react, to react, increasing the rate of collisions increases the rate of increasing the rate of collisions increases the rate of reactionreaction..

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Reaction progress Reaction progress

Disappearance ofDisappearance ofREACTANTSREACTANTS

Formation ofFormation ofPRODUCTSPRODUCTS

http://boomeria.org/chemlectures/rates/rates.htmlhttp://boomeria.org/chemlectures/rates/rates.html

Rates of CombustionRates of CombustionSlow combustion: Slow combustion: the stove to the right is the stove to the right is

designed for the slow burning of fuels such designed for the slow burning of fuels such as large pieces of coal or wood.as large pieces of coal or wood.

vega.soi.city.ac.uk vega.soi.city.ac.uk

Fast combustion: Fast combustion: the the burning of methane in a burning of methane in a Bunsen burner is a fast Bunsen burner is a fast reaction.reaction.

Explosive combustion: Explosive combustion: an an explosion is the fastest explosion is the fastest combustion where all of the fuel combustion where all of the fuel is ignited almost instantly.is ignited almost instantly.

encarta.msn.com encarta.msn.com

www1.sedo.energy.wa.gov.au www1.sedo.energy.wa.gov.au

Some Factors Affecting Some Factors Affecting Reaction RatesReaction Rates

• TemperatureTemperature– Higher temperature means particles have more kinetic Higher temperature means particles have more kinetic

energy, leading to an increase in reaction rate.energy, leading to an increase in reaction rate.• ConcentrationConcentration

– Increasing the concentration of the reactants increases Increasing the concentration of the reactants increases the chance of collisions, which increases the rate of the chance of collisions, which increases the rate of reaction.reaction.

• Surface areaSurface area– Fine powders have more surface area than large Fine powders have more surface area than large

pieces leading to more collisions. For this reason, fine pieces leading to more collisions. For this reason, fine powders create an explosion hazard when mixed with powders create an explosion hazard when mixed with airair

• CatalystsCatalysts– As previously stated, catalysts lower the activation As previously stated, catalysts lower the activation

energy, therefore increasing the rate of reactionenergy, therefore increasing the rate of reaction

Catalysis: Industrial Examples

Catalytic Converter:Catalytic Converter: Rhodium and Rhodium and platinum catalysts are coated on a platinum catalysts are coated on a ceramic honeycomb block to ceramic honeycomb block to remove unburnt hydrocarbons, remove unburnt hydrocarbons, nitric oxide and carbon monoxide nitric oxide and carbon monoxide from motor vehicles.from motor vehicles.

www.chem.brown.edu www.chem.brown.edu

The Haber Process:The Haber Process: The production of The production of ammonia from nitrogen and hydrogen ammonia from nitrogen and hydrogen gases is catalysed by an iron catalyst.gases is catalysed by an iron catalyst.

NN2(g)2(g) + H + H2(g)2(g) NH NH3(g)3(g)

FeFe

cwx.prenhall.com/.../media_portfolio/14.htmlcwx.prenhall.com/.../media_portfolio/14.html

8.5 Energy8.5 EnergyCompiled by: Robert Slider (2006)Compiled by: Robert Slider (2006)Please share this resource with othersPlease share this resource with others