chemistry - module 4 - energy

8/11/2019 Chemistry - Module 4 - Energy

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Chemistry Module 4 Energy

1. Living organisms make compounds which are important sources ofenergy.

Outline the role of photosynthesis in transforming light energy to

chemical energy and recall the raw materials for this purpose.

Photosynthesis is the process by light energy is trapped by the chlorophyll in theplants leaves and is used to transform the raw materials of carbon dioxide andwater into glucose and oxygen. Photosynthesis occurs in all green plants and isthe source of life of all organisms. Without photosynthesis, no organism would beable to use the suns energy, thus everything would perish.

Light

Carbon Dioxide Water !lucose "xygenChlorophyll

Photosynthesis is an endothermic reaction as it absorbs energy from sunlight

#t is the process by which light energy is converted into chemical energy which isstored as glucose. #t occurs only in green plants.

When the above chemical reaction occurs, $%&'() of energy is absorbed per moleof glucose formed. *hus the overall role of photosynthesis is to capture the lightenergy of the sun and transform it into chemical energy which is stored in plants.

outline the role of the production of high energy carohydrates from

caron dio!ide as the important step in the stailisation of the sun"s

energy in a form that can e used y animals as well as plants.

Carbohydrates are compound of hydrogen, carbon and oxygen. Common

carbohydrates include glucose, starch and cellulose.

Photosynthesis is a complex multi+step reaction brought about by the chlorophyllin the leaves plants. *hus the energy that is captured by the plant is chemicallystored in glucose.

Carbohydrates in plants are the energy source of animals.#n cellular respiration,the stored chemical energy is made available to the organism through thefollowing euation-

!lucose "xygen Carbon Dioxide Water nergy

*he amount of energy released during respiration is the same as was absorbedduring photosynthesis, namely $%&'() per mole of glucose. /ome of this energy

is used for daily activities whereas the ma0ority is dissipated as heat. 1 smallportion of this energy is transformed into protein and fat 2or lipids3.

Carbohydrates are considered to be high energy compounds because when theyreact chemically as in respiration they release large amount of energy.

#ote$4irtually all the solar energy trapped by plants ends up as heat in theenvironment to be re+radiated into space.

#ote$*he longer the food chain, the more inefficient it is.

1ll forms of life on arth are dependant upon sunlight for their supply of energy5without the sun there would no life as we (now it. Production of carbohydrates byphotosynthesis is the main way in which solar energy is collected for use by plant.


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%dentify the photosynthetic origins of the chemical energy in coal&

petroleum and gas.

Plants harvest solar energy to live and grow, and animals live eating plants.6ormally, when plants and animals die, they are decomposed and they areconverted bac( into carbon dioxide, water and nutrients which are released bac(

into the environment, so completing the materials and energy cycles that are partof the living world.

7owever in certain locations, instead of being fully decomposed to carbon dioxide

and water, some plant and animal material was only partially decomposed andremained stored in the arth as energy+rich compounds. *hese are (nown as

fossil fuels. *hey were mainly formed due to intense pressure and extremely hightemperatures for millions of years.

Energy rich compounds are those that release large amounts of energy whenthey undergo chemical reactions. *he stored energy is (nown as chemicalenergy. 8y burning fossil fuels we are able to release the stored chemical energy

within them. *he common fossil fuels are coal, crude oil and natural gas.

Living matter is mainly made up of compounds of carbon. *herefore fossil fuelswere naturally synthesi9ed by geological processes acting upon compounds of

carbon. *hus it is not surprising when we see that fossil fuels themselves arecompounds of carbon.

'ead (lants and )nimals

*nderground +emperature and (ressure for millions of years

,ithout -acterial )ction ,ith -acterial )ction

Coal /olid0 Crude Oil liuid0#atural 2as 2as0

*he origin of chemical energy in fossil fuels in form the sun. Living organisms

obtain energy directly or indirectly from the sun via photosynthesis.

process and present information from secondary sources on the range of

compounds found in either coal& petroleum or natural gas and on thelocation of deposits of the selected fossil fuel in )ustralia

3uel Maor )ustralian 5esources

8lac( coal 8owen 8asin in :ld *here is very little coal in the

/ydney 8asin in 6/W western half of the continent.8rown coal Latrobe 4alley in 4ictoria

6atural !as !ippsland 8asin ; 4ictoriaCooper 8asin ; /outh 1ustralia

Crude "il 8ass /trait in 4ictoria 2will be exhausted in a few decades3.

Coal is a particularly important fossil fuel 6/W as we use it to generate most ofour electricity. 8urning coal produced steam which drives the turbines to ma(eelectricity. Coal is found in every state in 1ustralia, but 6sw, 4ic and :ld are ourmain producers.

Coal is a rot consisting mainly of carbon 2


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6. +here is a wide variety of caron compounds.

%dentify the position of caron in the periodic tale and descrie

its electron configuration.

*he element Carbon is located in group A of the periodic table. #t is also located inperiod $ and has atomic number of B. Carbons electron configuration is $,A

indicating the presence of four valence electrons. Carbon is a non+metal but isable to conduct electricity when in the form of graphite.

'escrie the structure of the diamond and graphite allotropes and

account for their physical properties in terms of onding.

When an element exists as more than one crystalline form, those forms are(nown as allotropes. 1llotropes are forms of the one elements 2in the samephysical state3 which have significantly different physical properties 2such asdensity, hardness, electrical conductivity and colour3. *here are eight main

allotropes of carbon-

%. Diamond%%. graphite

%%%. lonsdaleite

%7. single+walled carbon nanotube 2also (nown as buc(ytube37. 8uc(minsterfullerene 2also (nown as buc(yball3

7%. C


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-elow is a summary of the properties of 'iamond$

(roperty E!planation in terms of onding

8ard *hree+dimensional lattical structure 2the tetrahedral arrangement of the carbon

atoms arranged systematically in layers that are not flat3 and strong covalentbonds between the carbon atoms that extend across the lattice, give strongintermolecular bonds which are extremely difficult to brea( ensuring hardness ofdiamond.

8igh M.(. and-.(. #t reuires huge amounts of energy to rupture the strong intermolecular bonds

between the carbon atoms due to its covalent networ( structure in which strong

covalent bonds are extended throughout the lattice, the melting points and boilingpoints must be high.

+ransparency *he carbon atoms are arranged in orderly fashion throughout the entire crystal.*his gives the diamond its transparency as light is able to pass between the atoms

giving the diamond its colourless appearance and high light+refractive indexma(ing it extremely attractive.

#on9conductor ofelectricity

Diamond is a covalent networ( substance, this means that the bonds between thecarbon atoms are covalent bonds. *his means that the valence electrons of thecarbon atoms are not free to move and since there are no mobile electron there isno conduction of electricity.

Minimal

chemicalreactivity

#n order for substances to be reactive they must be able to transfer their electronseasily. #n diamond, the electrons are tightly bound due to the covalent bonds,

therefore they are unable to move or be transferred to other elements, givingdiamond a very low reactivity.

8igh 'ensity *he structure of the diamond shows that the atoms are tightly bound in a strongthree dimensional lattical structure. 1lso the six+membered rings are stac(ed ontop of one another, giving diamond a high density 2&.


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*he structure of graphite is significantly different to the structure of diamond andthus its physical and chemical properties are different as well. !raphite is also acovalent networ( solid 2covalent lattice3 li(e diamond but in this case each carbonatom is only three other carbon atoms 2in diamond it was bound to four3. *hisforms a planar structure as shown in the figure above.

ach ring consists of six carbon atoms which is also evident from the diagram.

/ince each carbon atom only has three other carbon atoms attached to it, it mustmean that one electron is not covalently bonded 2i.e it is free3. *hese extra

valence electrons form a sea of delocalised electrons similar to that in metals. #tis the presence of the sea of delocalised electrons which ma(es graphite an

electrical conductor 2since the electrons can move when influence by an appliedvoltage similar to that in metals3. 7owever, electricity is only conducted along theplane of layers, graphite does not conduct electricity at =' degrees to the plane.*his is simply because the sea of delocalised electrons are only able to moveacross the planes and not 0ump from one plane to another.

#t can also be seen that the two+dimensional lattices are pac(ed one upon the

other as shown in the figure above. /ince, there are only wea( intermolecularforces between the layers, they can easily slide across one another, and this

explains the slippery+ness of graphite and its good lubricating characteristics.

1nother phenomenon when it comes to graphite is that every second layer isstac(ed identically upon each other.:*he crystal structure of graphite amounts toa parallel stac(ing of layers of carbon atoms. Within each layer the carbon atomslie in fused hexagonal rings that extend infinitely in two dimensions. *he stac(ingpattern of the layers is 18181...5 that is, each layer separates two identicallyoriented layers.; 1

8elow is a /ummary of the properties of graphite$

(roperty E!planation in terms of -onding

/lippery2ood Luricant0

1s previosuly explains, the carbon atoms in graphite are connected inhexagonal rings which connect to form a layer. *hese layers are thenpiled one on top of the other. *he forces that hold these layerstogether are (nown as the van der Waals forces. *hese forces areextremely wea( and the layers are seperated by a large distance. Due

to these two factors the layers can slip over each other easy giving

graphite its slippery nature and ma(ing it a good lubricant.

1

Fcarbon.F ncyclopGdia 8ritannica. $''=. ncyclopGdia 8ritannica "nline. ' )un. $''=

HIL- http-EEwww.britannica.comE8chec(edEtopicE=A&$Ecarbon


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E!tremely soft

sustance

*he structure of graphite explains why it an extremely soft substance .*his is because despite having strong covalent bonds between carbon

atoms in each layer, the forces between layers are extremely wea(24an de Waals forces3. *his allows layers of carbon to slide over eachother in graphite ma(ing the substance very soft and greasy.

Medium 'ensity6.< g=mL0

!raphites density is less than that of diamond. *his is due to thestructural layout. *he layers are seperated by large distances due tothe wea( van der Waals forces which are unable to tightly bind thelayers together. Due to this the carbon atoms are more spread out,reducing graphites density.

8igh M.(. and -.(.!raphite can be considered as a covalent networ( substance despiteno bonding in the vertical direction. *he carbon atoms are connected

via strong covalent bonds which extend throughout the hori9ontallattice. *hese intermolecular bonds are hard to brea( and thus more

energy is reuired to brea( them. Conseuently, the melting andboiling points of graphite are high.

2ood ElectricalConductor

#n graphite, each carbon atom only has three other carbon atomsbound to it via single bonds. *herefore it must mean that one electronis not covalently bound 2i.e it is free3. *hese extra valence electronsform a sea of delocalised electrons similar to that in metals. #t is thepresence of the sea of delocalised electrons which ma(es graphite anelectrical conductor 2since the electrons can move when influence by

an applied voltage similar to that in metals3. 7owever, electricity isonly conducted along the plane of layers, graphite does not conduct

electricity at =' degrees to the plane. *his is simply because the sea of

delocalised electrons are only able to move across the planes and not0ump from one plane to another.

#ote$

:ffect of heat- it is the most stable allotrope of carbon. 1t a temperature of $


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*se (ropertyies0 related to use

>ewellery Lustrous, 7igh Light Iefractive #ndex, /cratch resistant, 7ard,

*ransparent

%ndustrial purposes

like cutting tools

7ardest (nown substance on arth which means it can cut through any

substance, high melting point also allows it to be used in hotenvironments.

8eat sinks

7ighest thermal conductivity of any substance which allows it to uic(lyextract heat from sensitive areas eg. Computer chips have a diamond

layer that is able to uic(ly remove heat from the area. 1lso, highmelting point.

)rasives 7ard, /cratch resistant

,ear resistant parts Iesistant to corrosion, low chemical reactivity

Low frictionmicroearings

*hese are needed in extremely small mechanical devices. Diamondbearings are used when extreme abrasion resistance and durability areessential.

'iamond windows transparent, very durable and resistant to heat and abrasion, hard2security3

'iamond /peaker'omes

4ery stiff material 2hard3, also rapid vibrations will not causedeformation, therefore it enhances the performance of high ualityspea(ers.

*ses of 2raphite

*se (ropertyies0 related to use

:Lead; (encils /oft and slippery nature, layers can easily be separated

5efractory cruciles 7igh melting and boiling points, when mixed with other substances itcan become extremely hard.

Electrodes !ood electrical conductivity, high melting point

(olishes and paints /oft, slippery nature, metallic luster

Luricant in machines /lippery nature, high melting points, greasy nature since layers can beeasily separated.

Electrotypes forprinting

!ood electrical conductivity, high melting point, soft nature so can bemade into a fine powder that is still able to induce an electrical current.

'ry cell atteries !ood electrical conductivity, high melting point

%dentify that caron can form single& doule or triple covalent

onds with other caron atoms.

Carbon atoms are able to form single, double or triple covalent bonds with other

carbon atoms.


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When one pair of electrons is being shared it is (nown as a single bond.When two pairs of electrons are being shared it is (nown as a double bond.When three pairs of electrons are being shared it is (nown as a triple bond.

When a hydrocarbon contains only single bonds it is (nown as an al(ane and its

molecular formula can be calculated using Cn7$n$where n is the number of

carbon atoms.

When a hydrocarbon contains one or more double bonds it is (nown as an al(ene

and its molecular formula may be calculated using Cn7$n

When a hydrocarbon contains one or more triple bonds it is (nown as an al(yne

and its molecular formula may be calculated using Cn7$n+$

#ote$ #f a hydrocarbon is in the form of a ring it is (nown as a cyclichydrocarbon. or example pentane in cyclic form would be (nown as

cyclopentane.

E!plain the relationship etween caron?s comining power and

aility to form a variety of onds and the e!istence of a largenumer of caron compounds.

Carbon forms a huge range of compounds. *here are more compounds of carbonthan of any other element 2despite hydrogen because it is almost always present

in carbon compounds3. *here are eight main explanations why the ma0ority ofcompounds (nown to chemists are carbon compounds. *hese are-

- Carbon readily forms carbon+carbon bonds

- *hese bonds may be either single, double or triple or a combination ofthem

- Carbon forms cyclic compounds as well as straight and branched chain

compounds.

- *he intramolecular bonds 2covalent bonds3 combining the atoms in carbon

compounds are strong. *hese strong intramolecular bonds can help theformation of millions, and even billions of (inds of molecules.

- Carbon is able to form compounds that are stable and durable. or this

reason it is able to form a vast array of compounds.

- Due to the formation of isotopes, there may be many carbon compounds

with the same molecular formula, yet have different structural formulae.*hus they are regarded as different substances or different compounds.

- *here is no limit to the amount of carbon atoms in a chain they bondindefinitely due to the high combining power of carbon.

- Carbon it is able to form four covalent bonds which can arise in different

directions allowing for complex organic compounds to be created.

Hnder all circumstances, carbon always forms four covalent bonds. *he fact that it

has four valence electrons means that it is able to lose or gain electrons. *hismeans that it can readily combine with both non+metals and metals.


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'escrie the use of fractional distillation to separate the components of

petroleum and identify the uses of each fraction otained.

Crude Oil is a complex mixture of hydrocarbons formed by geological action ondecayed auatic plant and animal matter over millions of years. "il accumulates

under domes of impervious roc( hundreds to thousands of meters below thearths surface. #t has to be refined before it can be used.

*he first step in oil refining is fractional distillation. or separating componentsof crude oil it is carried out in large steel towers up to A' meters high. *hus,

during this process, the components of oil are separated according to their boilingpoints. /ince boiling point increases as the molecular weight increases, the

separation is roughly in order of increasing molecular weights. Crude oil isvapori9ed and then fed into a fractionating column. *he temperature falls as thevapour rises up through the column. *hus the least volatile components condensenear the bottom. *hese liuids are collected at various heights and these are(nown as the various ractions.

3raction -.(. C atoms=molecule *ses

!ases M&' ?+A Liuefied Petroleum !as 2LP!3

Petroleum ther &'+%'


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atoms 0oined together in one string so that no carbon atom is 0oined to more thantwo other carbon atoms.

#n addition there are branched+chain al(anes with carbon s(eletons where onecarbon atom is attached to at least three other carbon atoms.

Compare and contrast the properties of alkanes and alkenes C1 C@ anduse the term homologous series to descrie a series with the samefunctional group.

1 family of compounds which can be represented by one general molecularformula is called an homologous series.

)lkanes$

*he simplest al(anes 2C?+ CA3 are gases at room temperature. 1l(anes with


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hydrogen by brea(ing the double bond and forming single bonds to extrahydrogen atoms i.e converting them to al(anes3.

1l(anes are generally more reactive than al(anes.

e!plain the relationship etween the melting point& oiling point andvolatility of the aove hydrocarons& and their non9polar nature andintermolecular forces dispersion forces0

Look in above dot point.

5ecap$

ven though not all al(anes are strictly symmetrical, al(anes are still (nown asnon+polar molecules. *his is because C+C bonds are non+polar, C+7 bonds areslightly polar but they are mostly cancelled out due to the structure of the al(ane.*his lac( of polarity accounts for al(anes being insoluble in water 2a polar

solvent3.

*hus the only intermolecular forces between al(ane molecules are dispersionforces. *hese are uite wea(, thus it is easy to separate the molecules. *hus

al(anes have low melting and boiling points.

#ote$ 'ispersion forces increase as molecular weight increases.

*he 7olatility of a substance is the ease with which it can be converted to avapour. 4olatility increases as boiling point decreases. /o for al(anes, volatilitydecreases as molecular weight increases.

*he straight chained al(enes have similar physical properties to the al(anes.

)ssess the safety issues associated with the storage of alkanes C19C@ in

view of their weak intermolecular forces dispersion forces0.

1l(anes, particularly low molecular weight ones such as C?+C% are extremelyflammable. #n addition at high concentrations they can be toxic 2poisonous3. 1nadded ha9ard is the high volatility 2low boiling points3 of the liuid ones, whichmeans that if a container is left open to the atmosphere, the liuid uic(lyevaporates and forms a flammable or explosive mixture in the air.

/afety (recautions include$

+ Well maintained cylinders and fittings for gaseous hydrocarbons.@ethane and ethane are non+condensable gases ate room temperature

and are therefore stored in high pressure cylinders which provide enoughpressure to overcome the boiling effect and (eep them as a liuid.

+ 1dd odours that are pungent in order to uic(ly detect if there is a lea(.

+ /turdy 2preferably metal3 containers for liuids stored in a wellventilated area in case of a lea(age.

+ @inimi9e the uantity in use. *his will ensure that there is minimal ris( ofa ha9ardous situation arising. 1lso, if large amounts are being used, they


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should be stored away from populated areas and in a located that is wellmaintained and ventilated

+ Neep al(anes away from na(ed flames or spar(s. *he al(anes must bestored in areas where there is no instance of a na(ed flame or hotfilaments. *his is to ensure that no accidental combustion occurs as it

could be potentially dangerous. 1lso, ensure that all electrical euipmentbeing used does not produce spar(s.

+ 1lways handle in well ventilated areas. Due to the poisonous nature of

these substances it is dangerous to use them in confined areas. *heyshould be handled outdoors when ever possible.

+ransportation$

9 *he fuel tan( is located at the end remote from the hot engine and isoutside the main shell of the vehicle.

9 *he fuel tan( has narrow inlet and outlet pipes, which are both at the topof the tan( to minimi9e chances of lea(age during accidents5 fuel has to

be pumped from the tan( by the engine so that in most cars even a fuelline rupture will not cause rapid lea(age of petrol.

9 When the petrol is transported by road or rail, heavy steel tan(s areused. *hese are well sealed and are designed to withstand mostcollisions or overturnings without rupture of the tan(.

9 eatures are placed in vehicles to dissipate or prevent any build up of

static electricity.

9 *he fuels are also dyed for easy identification in case of lea(s. g.Hnleaded petrol is colored blue.

4. Comustion provides another opportunity to e!amine theconditions under which chemical reactions occur.


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'escrie the indicators of chemical reactions

Chemical changes are also called chemical reactions. Common indicators that achemical reaction has occurred are-

- %f a gas is produced. or example when copper carbonate is decomposed

under the influence of heat it produces carbon dioxide whose presence can bedetected using the limewater test.

- %f a precipitate is formed. or example when two solutions are mixed, suchas sodium chloride and silver nitrate, silver chloride, which is a white solid

forms.- %f there is a permanent colour change. or example when potassium

permanganate solution 2which is originally purple3 is combined with hydrogenperoxide, the mixture produced is colourless, indicating a chemical reaction.

- +emperature change in the mi!ture is uite significant. or examplewhen magnesium ribbon is burnt in air, the metal becomes extremely hot

- 'isappearance of a solid. *his is not 0ust the dissolution of one solid in aparticular solvent but rather a complete re+arrangement of elements in order

to produce new substances. or example when magnesium hydroxide powderis combined with hydrochloric acid, a clear solution is produced.

- #ew sustances are created. or example the electrolysis of water. Wherewater 27$'3 is decomposed into hydrogen gas 27$3 and "xygen gas 2"$3

- 8eat or light is given off. or example, when a piece of magnesium ribbonis burnt in air, significant amounts of light and heat energy are emitted,

leaving a white powder behind.- 'ifficult to reverse the process.or example when wood is burnt, it turns

into ash and gases evolve. 1fter the wood has completely burnt burned, itcannot be restored to its original form.

- )n odour is produced. or example when sodium hydroxide is added to a

solution of ammonium chloride the pungent odour of ammonia is clear.

%dentify comustion as an e!othermic chemical reaction

:Comustion is a process in which a self sustaining chemical reaction occurs attemperatures above those of the surroundings. @ore simply, combustion isburning. xplosions are also a form of combustion. 1ll combustion reactionsliberate large amounts of heat. *hey are called e!othermic reactions.J

chemistry - module 4 - energy

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