Chem Topic C

Energy

the ability to do work

In what units is energy measured?

Joules (J)

Useful energy sources:

release energy at a reasonable rate and produce minimal pollution; must be in concentrated form

First Law of Thermodynamics

states that energy cannot be created or destroyed, only converted from one form to another

What happens as energy is converted from one form to another?

the quality of energy becomes degraded as heat is transferred to its surroundings

In a coal-fired power station;

energy in coal goes from a concentrated form to a dispersed form and becomes less useful

Non-renewable energy resources

finite resources that will run out in the near future

Renewable energy sources

naturally replenished

Types of non-renewable energy sources

fossil fuels, nuclear fission, electrochemical cells

Types of renewable energy sources

solar, wind, hydroelectric, geothermal, biomass, tidal, nuclear fusion

Solar power

renewable and sustainable but not available at night

Wind power

renewable and sustainable but unsightly and create noise

Hydroelectric

renewable and sustainable but large areas of land are flooded to create reservoir

Geothermal

renewable and sustainable but only suited to particular regions

Tidal

renewable and sustainable but can disrupt fish migration

Biomass

only renewable and sustainable if crops are regrown, but land used to grow biomass crops could be used to grow food crops instead

nuclear fusion

Potentially unlimited - joining hydrogen nuclei together with the release of a large amount of energy.

Coal, oil, natural gas (aka fossil fuels) are

non-renewable energy sources that are finite

Fuel

substance that releases energy when it undergoes a chemical or nuclear reaction

nuclear fission

A nuclear reaction, in which uranium is bombarded with neutrons, produces heat. The heat can be used to generate steam to turn a turbine, which turns a generator to produce electricity.

electrochemical cells

Redox reaction used to produce an electrical current

Specific energy

the energy produced per unit mass

Specific energy equation

energy released(enthalpy change)/mass of fuel consumed(molar mass)

Energy density

energy produced per unit volume

Energy density equation

energy released(enthalpy change)/volume of fuel consumed(molar/density)

Standard enthalpy change of combustion

the enthalpy change when one mole of substance is burned in excess oxygen under standard conditions

The higher the specific energy and energy density

the more effective

The higher the energy density of the fuel

the more energy may be stored/transported for the same amount of volume

Is energy transfer 100% effective?

no, some energy is transferred as heat to its surroundings

efficiency equation

(useful output energy/total input energy) x 100

How would the energy transfer process be more efficient?

if it transfers a greater percentage of the total input energy to the useful output energy required

Energy is transferred in the direction in which

it goes from a more concentrated form to a less concentrated (dispersed) form

Fossil fuels

formed by the reduction of biological compounds that contain carbon, hydrogen, nitrogen, sulfur and oxygen

How were fossil fuels formed?

from the remains of dead organisms in anaerobic conditions

How was coal formed?

fossilised plant material containing mainly carbon (80-90%), with hydrogen, nitrogen, and sulfur

How was oil and natural gas formed?

dead marine organisms

Process of coal formation

1. giant plants are in swamps 300 million years ago
2. plants become buried under layers of sediment and water
3. coal is formed under high heat and pressure

Types of coal

peat, lignite, soft bitminuous coal, anthracite (hard coal)

Which types of coal have a higher carbon content?

left to right \= lowest to highest

What increases the carbon content in coal?

increasing heat and pressure

Formation of crude oil and natural gas process

1. sea creatures and plants die and are buried in the sea floor
2. remains are buried deeper, high heat and pressure forms oil and natural gas
3. oil and gas deposits are reached by drilling on land at sea

What is crude oil?

complex mixture of straight chain, branched, cyclic and aromatic hydrocarbons (crude oil, petroleum)

What is natural gas?

methane, with varying amounts of ethane, propane, and butane as well as hydrogen sulfide

Petroleum

complex mixture of hydrocarbons that can be split into different component parts called fractions by fractional distillation

Why is Sulfur removed from crude oil

Prevent poisoning catalysts by blocking their active sites, crude oil needs to be refined

How does crude oil become usable?

fractional distillation, refined through separation of different fractions

Fractional distillation of crude oil process

1. crude oil is separated depending on the boiling points of the different fraction
2. the different fractions are vaporized and rise up the distillation column
3. smaller molecules rise to the top, larger ones collect at the bottom

How do the different fractions rise up the distillation column in fractional distillation?

the level at which the fractions condense depends on their boiling point (which depends on their molar mass)

Small molecules of crude oil

have higher volatility

In fractional distillation, as molar mass increases

the strength of the intermolecular forces (london dispersion) between the molecules also increase

Fractions of crude oil (increasing carbon chains)

Refinery gases, gasoline, naphtha, kerosene, diesel oil, fuel oil, bitumen

In fractional distillation, \________ is required to overcome the attractive forces between the molecules so the \_______ \_______ increases

energy; boiling point

What does thermal and catalytic cracking involve?

longer chain hydrocarbons being broken up into shorter chain hydrocarbons

Example of thermal and catalytic cracking

C7H16 -\> C2H4 + C5H12

How is thermal cracking carried out?

at a temperature of 750 Celcius and a pressure of 70 atm

What does thermal cracking do?

gives a mixture of products with a high proportion of hydrocarbons with carbon to carbon double bonds (alkenes)

What does catalytic cracking use?

zeolite catalyst that allows cracking to take place at a lower temperatue (500C) and pressure

What occurs in a car engine?

a mixture of fuel and air is compressed then ignited by a spark

What is auto-ignition?

the premature ignition of the air and fuel mixture when compressed, causes knocking

What happens from auto-ignition?

the engine loses power and can be damaged

\________ \_______ \__________ have a greater tendency to auto-ignite and cause knocking

straight chain hydrocarbons

Octane number

a measure of a fuel's ability to resist knocking (auto ignite) in a car engine

The higher the octane number \=

the greater the resistance to auto-ignition

What are more resistant to auto-ignition?

branched hydrocarbons due to high octane number

\_________, \_____, and \_______ \_________ also have a lower tendency to auto-ignite

shorter chain, cyclic, aromatic hydrocarbons

Octane number increases with a \___________ in the carbon chain \________

decrease, length

Octane number increases in \________ hydrocarbons and \________ \_______ hydrocarbons

aromatic, cyclic

Isomerisation converts \________ \_______ hydrocarbons with \___ octane numbers into \_______ hydrocarbons with \_____ octane numbers

straight chain, low, branched, higher

\__________ isomers have a higher resistance to auto-ignition

branched

Isomerisation \______ the octane rating of gasoline

increases

Octane rating of 2,2,4-trimethylpentane

100

Octane rating of toluene

114

Problems of using aromatic compounds in fuels

Aromatic hydrocarbons can be carcinogenic

Process of Catalytic reforming

Cracking and unifying, polymerising, and isomerising

What is the catalyst of reforming

Metal catalyst like platinum and alumina at high temperature and pressure

Coal gasification

the process of converting coal into syngas

Syngas

mixture of carbon monoxide and hydrogen gas

Syngas formula

C(s) + H2O(g) -\> CO(g) + H2(g)
CO(g)+3H2 -\> CH4(g)+ CO2(g)

Environmental benefits of coal gasification

low SOx, NOx, and other emissions from burning coal-derived gases

Syngas can be processed to form \______ \______ \____ by reacting it with \________

synthetic natural gas, hydrogen

Syngas can also be processed to from synthetic natural gas by reacting \____ with \_____ with a \_____ catalyst

coal, steam, potassium hydroxide

Coal liquefication

the process of converting coal into liquid hydrocarbons for use as fuels

In \______ liquefication, coal is exposed directly to hydrogen at \____ \_________ and \_______ \______

direct, high temperatures (450C), high pressures (14,000-20,000kPa)

In \______ liquefication, coal is first made into \_______

indirect, syngas (H2+CO)

Fischer-Tropsch process

a method of producing a variety of liquid hydrocarbons from a series of catalyzed reactions using carbon monoxide and hydrogen gases as reactants

Fischer-Tropsch reaction

CO(g)+H2O(g) -\> CO2(g) + H2 (g)

The total amount of \_______ \_______ produced to directly and indirectly support human activities is expressed in equivalent tons of \________ \______

greenhouse gases, carbon dioxide

How is carbon dioxide produced?

during the combustion of fossil fuels

The \____ of CO2 produced can be calculated and the \_____ \______ of different fuels can be compared

mass, carbon footprint

A lower mass of a fuel \=

a lower carbon footprint

Advantages of Coal usage

1. Present in large quantities
2. Readily avaliable technology
3. Safer than nuclear power

Disadvantages of Coal usage

1. Contributes to acid rain and global warming
2. Coal mining is dangerous (explosions, effect on miors)
3. Dirty, produces dust and smoke

Advantages of Oil usage

1. Easily transported in pipelines
2. Convenient fuel for car usuage

Disadvantages of Oil Usage

1. Contributes to acid rain and global warming
2. Risk involved in tanker transport

Advantages of Natural Gas

1. Clean fuel
2. Easily transported
3. Higher energy released than coal or oil

Disadvantages of Natural Gas

1. Risk of explosions to leaks
2. Contributes to global warming
3. Limited Lifespan

Carbon capture and storage

1. Carbon dioxide from industrial processes captured
2. Carbon dioxide compressed
3. Compressed gas injected deep into rock formations for storage

Greener Energy

Energy that limits pollution and greenhouse emissions

Reducing SO2 emission

to prevent acid rain by removing sulfur in fossil fuels through scrubbing, filtering, or using polymers with sulfur receptors

Reducing NOx, CO, and benzene emissions

use a catalytic convertor to remove from petrol