Option C: EnergyOption C: Energy

Contents• What is energy?• Fossil Fuels• Nuclear Energy

• Energy is the capability to do work or required to do anything.

• Energy has many forms and can be changed from one form to another.

• The conservation of energy states that energy cannot be created or destroyed.

• Sources of energy can be hot bodies or release from fuels.

• Fuel is a substance that can release energy by changing its chemical or nuclear structure.

Disadvantages•Inefficient (only 30% efficiency).•Releases harmful solid carbon particles into the atmosphere.

What is it?•Biomass, is a renewable energy source made of biological material from living, or recently living organisms.•Energy is released by combustion (burning). Advantages

•Produces less pollution than fossil fuels.•Does not cause acid rain.•Can be found locally.•It is renewable.

Disadvantages•Harmful radioactive waste is created.•Uranium supplies may only last for another 50 years.•Non-renewable•Radiation may cause cancer

What is it?•Radiation is released from the nuclei of metal atoms.•The radiation can be used to generate electricity.

Advantages•Green House gases are not made.•Only a small amount of fuel is needed to create a lot of energy.

Disadvantages•Lots of wind turbines are needed to produce enough power.•Turbines can only be put in windy areas.•It is not always windy.•Some people don’t like the look of the turbines.

What is it?•Wind turbines are used to generate electricity from the wind.•The wind turns the large blades and the blades turn a generator.

Advantages•Wind is renewable.•Wind is free.•No greenhouse gases are made.•There are few safety risks.

Disadvantages•Solar panels are expensive.•When it is cloudy or at night there is not enough light.•Some people don’t like the look of solar panels.

What is it?•Solar power uses energy from the Sun.•Solar panels transfer the Suns energy to heat water.

Advantages•The energy from the Sun is free.•The sun does not produce greenhouse gases.•The sun will always be there during our lifetime.

Disadvantages•Solar cells are expensive.•They take up lots of space.•They only work in Sun light

What is it?•Solar cells use energy from the Sun.•Solar panels transfer the Suns energy directly into electricity.

Advantages•The energy from the Sun is free.•The sun does not produce greenhouse gases.•The sun will always be there during our lifetime.

Disadvantages•There are not many places where we can build geothermal power stations.•Harmful gases and minerals may occasionally come up from the ground below. These can be•difficult to control.

What is it?•Rocks under the ground are hot.•Water can be pumped through these hot rocks and warmed up.

Advantages•Geothermal energy does not produce greenhouse gases.•The energy source is free and will not run out.

Disadvantages•The dam is expensive to build.•By building a dam, the nearby area has to be flooded and this could affect nearby habitats.•If it does not rain much we may not have enough water to turn the turbines.

What is it?•Flowing water is used to turn a turbine which generates electricity.

Advantages•When the electricity is generated, no greenhouse gases are made.•The water used is free.•It is a renewable energy source.

Disadvantages•Small waves generate small amounts of electricity.•Electricity needs to be transported from the sea onto the land.•The equipment is expensive

What is it?•Waves force air in and out of a chamber.•The air causes a turbine to generate electricity.

Advantages•Waves are free and will not run out. •Wave power does not produce greenhouse gases.•There are very few safety risks.

Disadvantages•A dam to make the water flow through the generators might be needed.•Plants and animals that live nearby might get harmed•The tides only happen twice a day, so can only produce electricity at that time.

What is it?•Solar power uses energy from the Sun.•Solar panels transfer the Suns energy to heat water.

Advantages•Tides are free and will not run out.•No greenhouse gases are produced.•It is reliable because we know exactly when the tides happen.

• The energy density of a fuel is the energy produced per unit volume whereas the specific energy of a fuel is the energy produced per unit mass.

• The two terms are related via the density of the fuel.

• The primary sources are primary sources which are not used directly but converted into secondary sources such as electricity.

• The efficiency of an energy transfer needs to be known.

• Efficiency is determined using the following equation:

Efficiency = useful output energy x 100 total input energy

The Octane Number of a

Fuel

The Internal Combustion Engine

When the petrol and oxygen mixture ignites and explodes evenly and at the correct time the engine runs smoothly.

Engine Knocking

Knocking is noises coming from the car

It is a sign that the petrol and air mixture in the engine is burning too soon or not exactly as intended

This reduces the efficiency of the engine and over time can cause serious damage.

The Octane Number of a Fuel

The octane number of a fuel is describedas a measure of the tendency of the fuelto cause knocking or as a measure of thetendency of a fuel to resist auto-ignition.

Definition

The Octane Number of a Fuel

The higher the octane number the smoother it burns and the less likely knocking will occur.

The lower the octane number the less likely it burns smoothly and so the more likely knocking will occur.

Reference Hydrocarbons for assigning octane numbers

C

H

H

H

C

H

H

C

H

H

C

H

H

C

H

C

H

H

H

C

H

H

H

(Octane Number = 0)

Heptane

C

H

H

H

C

CH3

CH3

C

H

H

C

CH3

H

C

H

H

H

2, 2, 4 - trimethylpentane

(Octane Number = 100)

Octane Numbers of hydrocarbons

Octane

Octane Number = - 10

Heptane

Octane Number = 0

Octane Numbers of hydrocarbons

Pentane

Octane Number = 62

Hexane

Octane Number = 25

Conclusion 1

• The shorter the carbon chain the higher the octane number and the longer the carbon chain the lower the octane number

Octane Numbers of hydrocarbons

Octane

Octane Number = - 10

C

H

H

H

C

CH3

CH3

C

H

H

C

CH3

H

C

H

H

H

2, 2, 4 - trimethylpentane

(Octane Number = 100)

Octane Number = 100

Conclusion 2

• The greater the amount of branching in the chemical structure the higher the octane number and the less branching the lower the octane number

Octane Numbers of hydrocarbons

Benzene

Octane Number = 101 Octane Number = 97

Cyclohexane

Conclusion 3

• Ring & Aromatic Compounds have high octane numbers

Octane Numbers of other Fuels

Methanol

Octane Number = 113 Octane Number = 117

Ethanol

Ethanol used as a biofuel in Brazil

Conclusion 4

• Oxygen containing organic compounds (oxygenates) have very high octane numbers

Improving the octane number of a fuel – Addition of Lead Compounds

• For years adding lead compounds (like tetraethyl-lead) to fuels rapidly improved the octane numbers of those fuels.

• This no longer occurs as the addition of lead to petrol has been banned in Ireland since 2000.

Why Lead Compounds are no longer added to petrol

As Lead compounds destroy the catalysts which make up the catalytic converter of the car (automobile) Lead is a highly toxic

chemical to living things.

Refining the Octane Number of a Fuel

• There are 4 ways a fuel (or chemical) may be refined to improve the octane number of that fuel (chemical):

• 1: Catalytic Cracking• 2: Reforming• 3: Isomerisation• 4: Addition of Oxygenates

Catalytic Cracking

Cracking is the changing of long-chained hydrocarbons (like from heavy gas oil fraction) to more useful short-chained hydrocarbons

Reforming & Ring Formation (Dehydrocyclisation)

The structure of hydrocarbon molecules with low octane numbers is re-shaped to give molecules with high octane numbers

C

H

H

H

C

H

H

C

H

H

C

H

H

C

H

C

H

H

H

C

H

H

H

CH3

Heptane

Octane Number = 0

Ring Formation

Methylbenzene

Octane Number > 100

C

H

H

H

C

H

H

C

H

H

C

H

H

C

H

C

H

H

H

H

Hexane

Octane Number = 25

Reformed

CyclohexaneOctane Number = 83

Benzene

Octane Number > 100