Carbon Based Fuels

Activation Energy

Energy Required to break bonds of reactants so that the reaction can proceed

If activation energy is low

Reaction occurs faster - sufficient amount of energy required is low

e.g. explosives have unstable bonds, hence have low activation energy

Fast Reaction

Small activation energy (bonds are already unstable and have enough energy to react)

Slow reaction

Large activation energy (bonds are very stable - need large amount of energy to react)

1kj (in J)

10³J

1MJ (in J)

10⁶J

What is ‘J’

SI unit

Joules

Conversion between J, kJ, MJ

J*1000 = 1kJ

kJ *1000 = 1MJ

Chemical Reaction

Particles colliding and rearranging to form new particles with different energy levels

Chemical Energy

In between potential bonds between atoms, electrons

Repulsions between nuclei

repulsions between electrons

the more unstable the bonds are the more energy that can be combusted - if stable, not much can be combusted

e.g. fuel (C-H bond) - very unstable - small ignition can result in large combustion

Chemical Energy In Food

Has a lot of C-H and C-C bonds (highly unstable)

Turns into C=O bonds or H₂0 bonds (more stable)

Undergoes combustion

Law Of Conservation Of Energy

Energy cannot be created nor destroyed

Can transform (change forms) - retains the same energy

System

The actual chemical reaction (name for the reaction)

Surrounding

Everything else in the surrounding vicinity of the system

Exothermic

Releases energy from the system to the surrounding

Energy of reactants > Energy of products

Endothermic

Takes in energy from surrounding into the system

Energy of reactants < Energy of products

Condensing Gas - Liquid

Exothermic reaction

Must slow down particles and cool them down

Must push out excess kinetic and heat energy - released into surrounding

Enthalpy

Chemical energy (potential) of substance

Delta H

Exchange of heat energy between system and its surroundings under constant pressure

Enthalpy change

Measure of amount of energy stored or relaeased during chemical reaction

Exothermic Reaction (Enthalpy Change)

H_r > H_p

energy of reactants > energy of products

Enthalpy Change is negative

Delta H < 0

Endothermic Reaction (Enthalpy Change)

H_r < H_p

Energy of reactants < Energy of products (takes in energy)

Enthalpy Change is positive

Delta H > 0

Activated Complex

The highest point of the energy profile diagram (transition state)

Old bonds are partially broken and new bonds are partially formed - not yet products

has maximum possible energy in reaction (system)

not a stable molecule

Activated Complex In Relation To Reaction Rate

Can form prodcucts afterward

Can form reactants again (go back)

like a hill - can roll back or roll forward from peak

Catalyst

Lowers the energy of the activated complex (lowers the peak required to reach, less activation energy required)

Endothermic vs. Exothermic - Activation Energy

Endothermic - more energy - need to break the low, stable bonds in reactants

Exothermic - less energy - reactants are already high, unstable - small ignition suffices

Energy Profile Diagrams

Fuels

Has stored, potential chemical energy in them

Can be released easily through heat or power

Types of fuels

Solid - Wood, coal, charcoal

Liquid - kerosene, petrol, diesel

Gaseous - Biogas, hydrogen, methane

World Energy Needs

Used wood and extensive fossil fuels (90% today rely on fossil fuels)

Fossil fuels price increased due to it being finite resource

Considering alternative, quickly replenishable, reliable, sustainable, and cost-effective ways.

Renewable Energy

Natural resources, never run out, constantly replaced - used for energy

Not always sustainable - e.g. nuclear energy

Sustainable Energy

Energy with no depletion, no harm - always renewable

Renewable Fuel

A fuel that can be replenished naturally instead of geological timescales

Sustainable Fuel

A renewable and environmentally friendly fuel

Fossil Fuels

Formed by slow geological process of sediments of biomass millions of year ago

Formation of fossil fuels

Biomass buried under mud, sand and rock

Turns into hydrocarbons from normal structure

Can be considered as “trapped sunlight” as plants used sunlight as energy before decomposition (photosynthesis)

Carbon content during fossilisation

Carbon content increases (Hydrogen, Oxygen leave as water, carbon dioxide and methane)

Proportion of Carbon is higher - more energy is released when burnt

Anthracite - 90-95% only carbon (highest proportion)

Progression Of Wood

Peat - 60% Carbon

Brown Coal - 70% Carbon

Black Coal - 90% Carbon

When water is in fuel, net energy of output is lower

Vaporising Water

Some energy is used to boil the water from the energy source

Need to boil water, then convert to steam - depletes/wastes useful energy from source

Heat Value

Amount of energy released per mole, when the fossil fuel is combusted

Electricity From Coal

Water is boiled using coal, the steam is channeled to push turbines, and generates electricity

Why Coal Power Station Is Not Efficient

Heat Loss, friction in turbines, release of heat into the environment

Formation Of Crude Oil

Remains of dead animals

Covered by mud

Goes through permeable roks

Is stuck under impermeable rocks

Also has gas above it (natural gas - as it is less dense than oil)

Oil at top, as it is less dense than water (all alkanes)

How crude oil is seperated

Through Fractional Distillation

Fractional Distillation

Bulkier hydrocarbons condense at the bottom (vaporise slightly but still mostly stay as liquid) - smaller compounds go to the top in vapour state

condense when the temp is low enough (based on intermolecular forces and molecular weight)

seperates all/most hydrocarbons

Bottom Of Fractional Distillation Vessel

400 degrees Celcius

Natural Gas

Fossil fuel, non-renewable energy source - methane, ethane or propane (mainly)

Extraction Of Natural Gases

trapped in crude oil

trapped in coal deposits (CSG)

Obtained through fracking

Fracking

Injecting fluid, sand, water or other chemicals at high speed to create holes (fissures) in impermeable rock to get oil and gases.

Liquefied Petroleum Gas (LPG)

propane, butane become liquid under pressure

used as fuel

after removing propane butane, remaining gas is used as cooking gas (CH₄)

Electricity from Natural Gas

Gases in combustion expand (volume expands) to push turbine to create electricity

Higher value of energy than coal

emit less CO₂

Shale Gas

Gas held under impermeable rock retrieved by fracking

Coal Seam Gas

Gas held on by coal

Reaction Of Electricity From Natural Gas

CH₄ + 2O₂ ——> CO₂ + 2H₂O

natural gas is 96% methane, 4% CO₂

Biofuels

Made from recent biomass (not ancient fossils)

Is renewable

From natural sources

Not all are sustainable

3 main biofuels

Biogas

Bioethanol

Biodiesel

renewable, sustainable, near carbon zero

Originally produced through photo synthesis

lower CO₂ impact

Carbon neutrality

CO₂ absorbed is the same or similar to the CO₂ amount emitted

Carbon Neutrality - Biofuel vs Fossil Fuels

Biofuel:

releases carbon dioxide once taken in by plants (same amount, but in current timeframe)

Fossil Fuels:

releases carbon from many years ago - additional carbon dioxide in atmosphere - not carbon neutral

Bioethanol

Produced through fermentation of starch and sugar using catalysts (biological)

Steps of producing Bioethanol

1) From starch, enzymes break it down to glucose

2)From glucose (with yeast as catalyst) it turns into ethanol

C₆H₁₂O₆ — (with yeast)—-> 2C₂H₆OH + 2CO₂

Biological Catalysts

Produce fewer harmful by-products

Is biodegradable - no need for strong acids or removing solutions

E10 petrol

Blend of 90% Octane and 10% Bioethanol

Reduces consumption of petrol from crude oils (fossil fuels)

Biogas

Formed by anaerobic decomposition (hydrolysis - breaking larger compounds into smaller ones)

From manure, plants, veggie waste, farm waste

mainly CH₄ and CO₂

Uses of biogas

Warming/powering homes

Waste from biogas - rich fertiliser

Composition of biogas

Conflict of producing bioethanol

Is produced from sugarcane (is needed for consumption as well)

Must first harvest for consumption, remaining husks are still rich in sugar - can be used for bioethanol making - second-generation bioethanol

Electricity From Biofuels

Gas is used as fuel to boil water - steam pushes turbines

Less energy produces than natural gas

Operates on a small scale (local manure or waste is used - too big facility is too expensive)

Reaction for biogas (producing energy)

Combustion of methane

Production of biodiesel

Reaction between veggie oils or animal fats with methanol with a basic catalyst

The oils split and prduce glycerol

The oil is used

Glycerol

Sweet-substance, sticky, has ph of 7

Splits away during the process

Is the “backbone” of holding the oil or fat together

Saturated Biodiesel

Contains single C-C bonds

Closely packed and are stacked on top of each other

Solids at room temp - animal fats

Unsaturated Biodiesel

Contains C=C bonds or triple bonds

have weaker intermolecular bonds - liquids/gases at room temp

have “kinks” in structure - can’t stack closer

Monounsaturated Biodiesel

Contain one double bond (one kink) - typically liquids at room temp

Polyunsaturated Biodiesel

Contain multiple double bonds (multiple kinks) - typically gases at room temp

Weak dispersion forces (can’t pack closely)

Animal fat vs Plant-oil derived

Animal fat - higher melting point - saturated

Plant oil - Lower melting point - is poly or mono unsaturated - weaker dispersion forces

Coal

disad: non-renewabl, high emissions

adv: large reserves, easy transport, high energy content

Natural Gas

disad: non-renewable, limited, polluting - less than coal or petrol

adv: more efficient than coal, easy to transport, high energy content

Petrol

disadv: non-renewable, polluting (less than coal), limited

adv: high energy content, easy to transport

LPG

disad: non-renewable, polluting (less than petrol)

adv: high energy content, low cost, sperates from natural gas easily, fewer waste produced than petrol

Biogas

disad: low energy content, low supply of materials

adv: renewable, made from waste, low running cost, low waste disposal, co2 absorbed during photosynthesis

Bioethanol

disadv: low raw materials, low energy content,

adv: renewable, from waste, CO₂ is absorbed, smooth burning, less particulates than petrol

Low production Of Biogas In Australia

Competing resources: coal, LPG, natural gas - no need for biogas

Cost of infrastructure

It can’t easily be transported across long distances as it is of low density

Dillemma for sugarcane (bioethanol vs consumption)

Create fuel from sugarcane residues

use non-food plants for fuel (sorghum,switchgrass,algae)

Use higher yield crops (more sugarcane per land)

Balance quotas between fuel and food

Requirement for combustion reaction

fuel to burn

oxygen for fuel to burn in

energy to kick-start process

Combustion reaction type

Exothermic

Oxidation Reaction

Oxygen is oxidising agent (reduces)

Complete Combustion

In abundant oxygen

fuel + O₂ —→ CO₂ + H₂O

produces carbon dioxide

produces blue flame

more energy than incomplete combustion

Incomplete Combustion

Limited Oxygen Supply

fuel + O₂ —→ CO + H₂O

creates carbon monoxide (dangerous)

partial oxidation of fuel

produces yellow flame

less energy than complete combustion

Carbon Monoxide poisoning

Poisonous gas

Attaches to blood and haemoglobin (transporter of oxygen)

Hemoglobin can’t give oxygen - tissues are oxugen starved

10ppm - gives symptoms, 200ppm - drowsiness, dizzy, headache

Writing Combustion equations

balance carbon and hydrogens

if odd number - make as fraction, then multiply whole equation by 2 (for number of oxygens)

Balancing alcohol combustions

balance carbon and hydrogen

oxygens on right - 1

divide by 2 and put that as coefficient of oxygen (on lhs)

if odd, make as fraction (half) - multiply equation by 2

Heat Of Combustion H_C (under enthalpy)

Energy released by a fuel per mole, per g perL in SLC conditions

water produced must be liquid - are all in standard states - water is in liquid

Specifications of H_c

pure substances - in mols and grams (combustion is measured)

most fuels dont have specific formula and moalr mass

H_C is always negative as combustion is exothermic

measured in kJg^-1 kJL^-1 and MJ/tonne

Molar Enthalpy Change

coefficient of fuel * H_c

if more than one mole - multiply it to get the energy output

If coefficient of fuel = 1

delta H = H_C

overall enthalpy = enthalpy of combustion

Converting kJmol^-1 to kJg^-1

kJg^-1 - termed as energy content

kJmol^-1/molar mass = kJg^-1

kJg^-1 * molar mass = kJmol^-1

Wood (heat of combustion)

18 kJg^-1

Dried peat (heat of combustion)

25kJg^-1

Brown coal, dried (heat of combustion)

30kJg^-1

Black coal, dried (heat of combustion)

35kJg^-1