Y11 Chemistry Topic 4 Summary - Energy

5/24/2018 Y11 Chemistry Topic 4 Summary - Energy

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Year 11 Chemistry Topic 4 Syllabus Summary Energy1.1: Outline the role of photosynthesis in transforming light energy to chemical energy and recall the raw

materials for this process

Energy used today comes directly/indirectly from the Sun via photosynthesis.6CO2(g) + 6H2O(l) C6H12O6(aq)+ 6O2(g)

Using light energy trapped by chlorophyll, plants combine carbon dioxide and water to produce glucose, acarbohydrate, and oxygen.

This is an endothermic reaction that absorbs light energy and is changed into chemical potential energywhich is stored within the glucose molecules.

1.2: Outline the role of the production of high energy carbohydrates from carbon dioxide as the

important step in the stabilisation of the suns energy in aform that can be used by animals as well as

plants

The chemical energy stored in glucose and other carbohydrates can be made available for use by livingorganisms through respiration.

C6H12O6(aq)+ 6O2(g) 6CO2(g) + 6H2O(l)+ energy

Carbohydrates in plants are the energy source for animals. Apart from direct absorption of heat,photosynthesis is the only way in which the natural environment can absorb solar energy.

The amount of energy released during respiration is the same as was absorbed during photosynthesis,namely 2830kJ per mole of glucose.

1.3: Identify the photosynthetic origins of the chemical energy in coal, petroleum and natural gas

The main source of energy today is fossil fuels (coal, petroleum and natural gas). Plants, using the suns energy via photosynthesis, harvest energy from the sun to live and grow, and

animals receive energy by eating plants or other animals.

Usually when a plant or animal dies, it is broken down by decomposing bacteria mainly into CO2and H2O. Fossils fuels are substances which were formed by the action of high temperature and high pressure upon

decaying plant and animal matter over millions of years ago.

Instead of being fully decomposed to CO2

and H2O, some plant and animal matter was only partially

decomposed and remained stored in the earth as energy rich compoundsfossil fuels:

o Coal PeatEarly stage of coal, porous brown mass of partially decomposed matter, low % (50-

80) of carbon and high % of H2O.

Lignite (Brown Coal)Forms when peat is further compressed, about 60-75% carbon. Bituminous Coal (Black Coal)Denser and drier coal, 80-90% carbon. Anthracite (Hard Coal)Densest form of coal, 90-95% carbon, low moisture (2-5%). CokeArtificial form of coal, 100% carbon.

o Crude Oil Crude oil is a complex mixture of hydrocarbons, mostly derived from the buried remains of

marine organisms.

Crude oil contains such a large variety of hydrocarbons (C1 - C100) that it must be refinedbefore use through fractional distillation.


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o Natural Gas Natural gas is a mixture of methane (75-90%), ethane (5-10%), propane and butane (3-6%)

and trace amounts of other gases. Generally, ethane, propane and butane are extracted.

The ethane is used in the petrochemical industry while propane and butane are liquefiedunder pressure to produce LPG (Liquid Petroleum Gas).

1.4: process and present information from secondary sources on the range of compounds found in either

coal, petroleum or natural gas and on the location of deposits of the selected fossil fuel in Australia

2.1: Identify the position of carbon in the Periodic Table and describe its electron configuration

Carbon is in Group 4of Period 2and is element 6. It has 4 valence electronsin its outer shell.2.2: Describe the structure of the diamond and graphite allotropes and account for their physical

properties in terms of bonding

Diamondo Diamond is made of carbon atoms covalently bonded throughout a rigid tetrahedral structure.o Atoms are arranged in buckled/puckered 6 member rings.o It is extremely hard, is an insulator and has a brilliant lustre.

Graphiteo Graphite is made up of layers of carbon atoms covalently bonded to three other carbon atoms

forming a planar structure.

o Layers of these hexagonal rings are held only by weak dispersion forces.o The excess electrons form a delocalised electron cloud.o Graphite is soft and slippery, is a conductor of electricity and is a dull, black colour.

Buckminsterfullerene (known as buckyball)o Buckyball is made of a spherical structure of carbon atoms covalently bonded to three other carbon

atoms. Standard buckyball has formula C60.

o It has some delocalised electrons, but is less reactive than graphite.


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2.3: Identify that carbon can form single, double or triple covalent bonds with other carbon atoms

The large number of carbon compounds present is due to the large variety of carbon-to-carbon bonds. A single bond, CC is formed when 2 carbon atoms share a pair of electrons. The shared pair of electrons is

called a single bond. The 2 C atoms can rotate freely around the single bond.

A double bond, C=C if formed when 2 carbon atoms share 2 pairs of electrons. The 2 shared pairs ofelectrons together form a double bond. The 2 C atoms are held in a planar structure; around the double

bond, rotation is hindered.

A triple bond is formed when 2 carbon atoms share 3 pairs of electrons. The 3 shared pairs of electronstogether form a triple bond. The 2 C atoms are held rigidly with no rotation possible.

2.4: Process and present information from secondary sources on the uses of diamond and graphite and

relate their uses to their physical properties

Diamond:o Used asjewellerydue to their brilliant sparkle andhardness(they cannot be dulled by scratches as

gold and platinum can).

o Used in making drillsand cutting implements (e.g. circular saw blades for cutting tiles, bricks andsteel) due to its hardness.

Graphite:o Used as electrodes in ordinary and alkaline dry-cell batteries due to high electrical conductivity.o Used as electrodes in extracting aluminium from alumina.o Used as a dry lubricant (often on door catches in motor cars) and pencils due to its hardness, and its

slipperiness that makes it useful for these purposes (the planar layers slide over one another).

3.1: Describe the use of fractional distillation to separate the components of petroleum and identify the

uses of each fraction obtained

Crude Oil is a complex mixture of hydrocarbons formed by geological action on decayed aquatic plant andanimal matter over millions of years.


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Oil accumulates under domes of impervious rock hundreds to thousands of meters below the Earthssurface, and has to be refined before it can be used.

The crude oil is heated to about 400C to produce a hot vapour that enters the fractionating tower. As the vapour rises upwards, it cools down and the fractions with higher boiling points begin to condense

onto horizontal trays, while the other components keep rising upwards until the temperature is sufficiently

low for them to condense.

Thus the higher boiling point components, or those with longer carbon chains, tend to condense near thebottom while those with lower boiling points, or those with shorter carbon chains, condense at the top of

the fractionating column.


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3.2: Identify and use the IUPAC nomenclature for describing straight-chained alkanes and alkenes from

C1 to C8

PREFIX:Length of carbon chain. SUFFIX: -ane for alkanes, -ene for alkenes. SIDECHAINS:

o CH3 methyl, CH2CH3ethyl, CH2CH2CH3 propyl, (CH2)3CH3butyl, F fluoro, Cl chloro, Br bromo, I iodo. STEPS:

o Name the longest C chain.o Identify side chains and write in alphabetical ordero Multiple side chains indicated using di-, tri-, tetra-, pent- etco Number all side chains so that the sum is a minimum.o In alkenes, the double bond must be names with the lowest number. The side chains are named

relative to the double bond.

Number of Carbon Atom/s Alkane Alkene

1 Methane ------------------------

2 Ethane Ethene

3 Propane Propene

4 Butane Butene

5 Pentane Pentene

6 Hexane Hexene

7 Heptane Heptene

8 Octane Octene

3.3: Compare and contrast the properties of alkanes and alkenes C1 to C8 and use the term homologous

series to describe a series with the same functional group

Alkanes (CnH2n+2)o The alkanes make up a homologous series. This refers to a family of compounds with the same

functional group, in this case C-C.

o Small alkanes (C1- C4) are gases.o Larger alkanes (C5- ~C18) are colourless liquids.o Even larger alkanes (C20onwards) are waxy solids.

Relatively low MP and BP MP and BP increase with chain length Insoluble in water Low density Do not conduct electricity

Relatively stable Alkenes (CnH2n)

o The alkenes also make up a homologous series with the C=C functional group.o There is at least one double bond, meaning that at alkenes are unsaturated hydrocarbons.


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o Simplest alkenes (C2C4) are gases.o Larger alkenes (C5 - ~C17) are colourless liquids.

Relatively low MP and BP, lower than alkanes MP and BP increase with chain length Insoluble in water Low density Do not conduct electricity More reactive than alkanes

Homologous Series Suffix General Formula Functional group/ Bonding in C series

ALKANE -ane CnH2n+2 Single Bond C - C

ALKENE -ene CnH2n Double Bond C = C

3.4: Explain the relationship between the melting point, boiling point and volatility of the above

hydrocarbons, and their non-polar nature and intermolecular forces (dispersion forces)

Alkanes and alkenes are non-polar, meaning that the only intermolecular force between molecules is theweak dispersion forces.

As the chain length increases, so does the molecular weight, and the more likely that dispersion forces willform.

Dispersion forces increase with molecular weight, thus as the chain length increases, so do the melting andboiling points.

3.5: Assess the safety issues associated with the storage of alkanes C1 to C8 in view of their weak

intermolecular forces (dispersion forces)

Alkanes with low molecular weight are extremely flammable and can be toxic at high concentrations. Liquid alkanes have high volatilitythey evaporate quickly and form an explosive mixture with air. Storage:

o Use well maintained cylinders and fittings for gaseous hydrocarbons.o Add odorous components to help detect leaks (eg methyl-mercaptan).o Use sturdy containers to store liquids and gaseso Keep away from flames and sparkso Do not handle in confined spaceso Keep areas well ventilated and use fume hoods for prolonged use

Transporto Fuel tank located at the back of vehicleo Have narrow inlet and outlet pipeso Store in heavy steel tanks that are well sealed and able to withstand collision.

4.1: Describe the indicators of chemical reactions

Chemical changes involve the production of new materials. When wax is burnt in air (as in a burning candle),new chemical compounds, such as carbon dioxide and water, are formed. Mixing carbon dioxide and water

does not cause wax and oxygen to re-form.

General indicators of chemical reactions:o Production of gas bubbleso Formation of a precipitateo Formation of new substanceso Permanent change in colour


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o Change in temperatureo Change in odouro Release/absorption of energyo Process cannot be easily reversed (e.g. electrolysis)

4.2: Identify combustion as an exothermic chemical reaction

It is the process in which a self-sustaining chemical reaction occurs at temperatures above those of thesurroundingssimply put, combustion is burning.

The reaction involves a chemical reacting with oxygen to release significant amounts of heat energy anexothermic reaction.

Burning of coke (Carbon), petrol (Octane) and natural gas (Methane) are examples of combustion reactions. Being exothermic, during combustion, the enthalpy of the products is less than the enthalpy of the

reactants, i.e. H energy used to split bonds, the reaction is exothermic e.g.

combustion.

If energy released during bond formation < energy used to split bonds , the reaction is endothermice.g.electrolysis.

4.4: Explain that energy is required to break bonds and energy is released when bonds are formed

Bond-breaking is an endothermic process as energy must be supplied to break the chemical bonds inreactants.

Bond-making is an exothermic process as energy is released when particles collide and new bonds areformed.

4.5: Describe the energy needed to begin a chemical reaction as activation energy

For a reaction to occur, particles of reactant particles must collide with sufficient energy to disrupt the bondsof the reactant molecules.

Therefore, before a reaction can occur, an amount of energy known as the activation energy must beavailable to reactants to kick-start the reaction.

The activation energy is the minimum amount of energy that reactant molecules must possess in order toform products.

Unless this minimum collision energy is reached, the colliding molecules will just bounce off each other.4.6: Describe the energy profile diagram for both endothermic and exothermic reactions

For an exothermic reaction, the enthalpy of the products is less than the enthalpy of the reactants, i.e. H0.

The peak of both diagrams represents the activated complex or transition state.


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The enthalpy difference between the reactant enthalpy and the activated complex is the amount of energyneeded for a reaction to occur, known as the activation energy (Ea).

4.7: Explain the relationship between ignition temperature and activation energy

Most fuels do not just spontaneously combust. An energy input or spark is required to start a combustionreaction.

Ignition temperature of a fuel-air mixture is the minimum temperature to which the mixture must beheated in order for combustion to occur.

Most common fuels have a high activation energy, which can be thought of as a high activation energybarrier to reaction, which can only be overcome by a high ignition temperature.

Therefore, the higher the activation energy, the higher the ignition temperature and vice-versa.4.8: Identify the sources of pollution which accompany the combustion of organic compounds and

explain how these can be avoided

Carbon Dioxide:o When hydrocarbons are completely combusted, or sometimes when incompletely combusted,

carbon dioxide is produced.

o Carbon dioxide is one of the major gases known to contribute to the enhanced greenhouse effect (orglobal warming).

Carbon Monoxide:o When incomplete combustion occurs, carbon monoxide may be produced.o Carbon monoxide binds preferentially to haemoglobin rather than oxygen, reducing the amount of

oxygen being delivered to cells, which can be fatal to humans.

o Formation of carbon monoxide is common in petrol engines where there is not enough oxygen.o To avoid this problem, one way is to keep the air-to-fuel ratio high.o In engines this is not practical because it would increase the ignition temperature, so a catalytic

converter in the exhaust system converts CO to CO2 (equation is given below with oxides of

nitrogen).

Particulate Matter:o When incomplete combustion occurs, fine particles of soot or ash may be produced.o They are so small that they do no settle out of the air.o This causes visibility to decrease as a form of air pollution.o They also are respiratory irritants and cause damage to plants.o Also, soot is carcinogenic, and therefore, it is a major cause of cancer.


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o These particles can be removed by using electrostatic precipitators, which use high voltage to inducea charge on particulates, which are then attracted to a positive/negative plate and are removed.

Sulfur dioxide:o Sulfur dioxide is produced by sulfur impurities in fossil fuels, especially coals, which are released

when they are burnt.

S(s)+ O2 (g) SO2 (g)o SO2is a respiratory irritant that causes breathing difficulties.

SO2 (g)+ O2 (g) 2SO3 (g)

SO3 (g)+ H2O(l) H2SO4 (aq)

o This formation of acid rain causes damage to natural ecosystems and buildings and structures.Australian coal is in high demand because of its low sulphur content.

Oxides of Nitrogen (NOx)o Nitrogen and oxygen gas do not normally react with each other, but at high temperatures (>1000C)

they will combine to form nitric oxide, which then reacts with oxygen to form nitrogen dioxide.

N2 (g)+ O2 (g) 2NO(g)

2NO(g)+ O2 (g) 2NO2 (g)o These reactions occur in the high temperature environment of car engines and power stations,

emitting small amounts of both these gases.

o Nitrogen dioxide causes respiratory difficulties and damages organ tissue.o However, when sunlight acts on NO2producing ozone, this leads to photochemical smog and causes

reduced visibility, eye and respiratory irritation as well as damage to plants and animals.

NO2 (g) NO(g)+ O(g)

O2 (g) + O(g) O3 (g)

o Catalytic converters in the exhaust systems of cars can convert NO and CO into N2and CO2.2NO(g)+ 2CO(g) 2CO2 (g) + N2 (g)

4.9: Describe chemical reactions by using full balanced chemical equations to summarise examples of

complete and incomplete combustion

Complete combustion:C5H12 (l)+ 8O2(g) 5CO2 (g) + 6H2O(g)

Incomplete combustion:C5H12 (l)+ 6O2(g) 4CO(g)+ CO2 (g) + 6H2O(g)

C5H12 (l)+

O2(g) 3C(s) + CO(g)+ CO2 (g) + 6H2O(g)

C5H12 (l)+ 4O2(g) 3C(s)+ 2CO(g) + 6H2O(g)

5.1: Describe combustion in terms of slow, spontaneous and explosive reactions and explain the

conditions under which these occur

Combustion is a chemical reaction because:o Light and high levels of heat are released.o New substances are formed (CO2and H2O).o The process cannot be easily reversed.

Combustion reactions proceed at very different rates. Slow Combustion:

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o Occurs when we use big lumps of fuel and limit the supply of air.o Burning only occurs on the surface of the big lumps and its speed is controlled by the limited supply

of air.

o For example, coal and wood stoves burn for hours due to low surface area of the coal or wood, andthe limited oxygen available inside the stoves.

Spontaneous Combustion:o There is a large surface area of fuel exposed to an excess of oxygen and there is a good mixing to

stop oxygen concentrations becoming depleted near the surface of the particles.

o Gaseous fuel of vapourised liquid fuel is mixed with excess air and fuel is always in contact with O2.o The gaseous nature of the mixture and the high temperature ensures that combustion proceeds

rapidly.

o An example of fast combustion is in power stations, where ground-up coal is used in excess oxygen.o The combustion is spontaneous because there is a large surface area and an excess of oxygen

available.

o Another example isburning methane or LPG, which mix well with air since they are gases. Explosive Combustion:

o An explosion is just an extremely rapid reaction one that goes into completion within a fewmicroseconds.

o Liquid fuel is injected and vapourised into an excess amount of heated air.o A spark is used to ignite the heated mixture of petrol and air.o In most explosive reactions, the reactants are finely divided, existing as vapour, powder or dust,

increasing surface area and thus rate of reaction.

o An example of explosive combustion is in car engines where a spark is used to ignite a heatedmixture of fuel and air.

5.2: Explain the importance of collisions between reacting particles as a criterion for determining

reaction rates For a reaction to occur, the reactant particles (atoms, molecules, ions) must react with sufficient energy to

overcome activation energy barrier.

Anything that increases the rate of these particle collisions will increase the rate of reaction. Concentration

o An increase in reactant concentration means that there is an increase in the number of reactantparticles per unit volume.

o This will lead to an increased chance of collisions, leading to an increase in the number of collisionsper unit time.

oAlthough the same proportion of these reactions will be successful (given that nothing else ischanged), the greater rate of collisions results in a greater number of successful collisions.

o This increases the rate of reaction. SurfaceArea

o Surface area is an important factor for heterogeneous reactions.o If the surface area of a reactant is increased, more of the reactant molecules are exposed to

collision.

o Since particles must collide to react, this will lead to an increased rate of reaction. Temperature

o An increase in temperature leads to an increase in the average kinetic energy of particles.o Although the increased velocities of the particles lead to a greater rate of collision, the increase in

rate of reaction due to this is small.

o Temperature affects reactions mainly because a higher proportion of reactant particles will haveenergy above activation energy.


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o This means that a greater proportion of collisions will be successful collisions, leading to an increasein the rate of reaction.

Breaking big lumps of solid into smaller pieces:o This increases the surface area of the solid and consequently, the rate of collision increases as more

particles of the solid are exposed, increasing the rate of reaction.

Stirring:o Keeps the solid suspended in the solution or gas and exposes the maximum surface area of the solid

to the solute or gas.

o For reactions in a solution, stirring quickly replaces the solution in which the reactant has been usedup with a fresh solution, so that there is always plenty of solute for the solid to react with.

5.3: Explain the relationship between temperature and the kinetic energy of particles

Not all particles in a sample have the same amount of kinetic energy. Temperature is related to the average kinetic energy of the particles in a sample. As the temperature increases, not only does the average kinetic energy increase, but the proportion of

reactant particles with sufficient kinetic energy to react is increased, resulting in rate of collisions increasing,

causing an increase in the rate of reaction.

5.4: Describe the role of catalysts in chemical reactions, using a named industrial catalyst as an example

A catalyst is a substance that speeds up a chemical reaction by providing an alternative pathway with loweractivation energy.

They speed up a reaction without being consumed. H stays the same for the catalysed and uncatalysed reactions. The catalyst my change chemically during part of the reaction but is chemically, always the same at the end

of the reaction as it was at the beginning.

Examples of industrial catalysts:o Zeolites, which are porous aluminosilicate compounds that are used in the catalytic cracking of

hydrocarbons to turn longer chains of hydrocarbons into petrol.

o Magnetite, an iron-iron oxide catalyst is made by heating Fe3O4with small amounts of potassiumoxide, calcium oxide and aluminium oxide.

The mixture is ground to a powder, reducing some of the magnetite to elemental iron,leaving a highly porous catalyst with large surface area.

o The manufacture of nitric oxide, NO, by the Ostwald process is an important step in the industrialmanufacture of nitric acid.

The first step of this process used a platinumrhodium catalyst. Because the catalyst and reactants are in different phases, this process is an example of

heterogeneouscatalysis. The initial reaction is catalytic oxidation of ammonia: 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

5.6: Explain the role of catalysts in changing the activation energy and hence the rate of chemical

reaction

Catalysts are substances used to increase rate of reaction without being consumed in the net reaction, thusthey do not change the H of a reaction.

The catalyst allows the reaction to occur with less collision energy required, lowering the activation energybarrier required for a reaction.

As a result, a greater proportion of reactant collisions will be successful and the rate of reaction will increase. Homogeneouscatalysts are usually in the same state as the reactants.


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o They work throughout the bulk of the gas or aqueous solution. Heterogeneouscatalysts are usually in a different state to the reactants.

o They provide a surface on which the reaction occurs more rapidly than it does in the reactionmixture.

o Reactant particles are adsorbed onto the surface of the catalyst this weakens or breaks thechemical bonds.

o Reaction occurs and then the product particles are desorbed.5.7: Process information from secondary sources to investigate the conditions under which explosions

occur and relate these to the importance of collisions between reacting particles

Explosions occur when reactions become extremely rapid. This usually happens when there is good contact between reactant particles and when the reaction is highly

exothermic with high activation energy.

Once the reaction is initiated, it liberates energy, which heats up the reaction mixture. This makes the reaction go faster, releasing energy more quickly, so there is an extremely rapid escalation in

temperature and reaction rate, causing an explosion.

In order for the rate to increase in this way, there must be a good supply of oxygen available to the fuel,otherwise the fall in concentration of one reactant (oxygen) will slow down the reaction.

Large lumps of fuel such as coal rarely explode because they rapidly use up the oxygen available at theirsurfaces.

However, very small particles of flammable material dispersed through a volume of air have great potentialfor causing explosions.

The total surface area of the particles is large and each particle has a ready supply of oxygen available.5.8: Analyse information and use the available evidence to relate the conditions under which explosions

occur to the need for safety in work environments where fine particles mix with air It is important to ensure that there can be no build-up of concentrations of flammable particles. Formation of flammable dust should be minimised, and what does form must be efficiently removed from

the air.

Dust from obvious fuels such as coal that provides a risk, as well as dust from anything that can burnfromhandling grain such as wheat, or from processing fibres and textiles such as paper and cotton.

Y11 Chemistry Topic 4 Summary - Energy

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