Reactivity 1. What drives chemical reactions?
Reactivity : the way in which chemical reactions transform reactants into products .
Reactivity 1.1—Measuring enthalpy changes
Reactivity 1.2—Energy cycles in reactions
Reactivity 1.3—Energy from fuels
Reactivity 1.4—Entropy and spontaneity (Additional higher level)
Reference : chemistry guide ,Pearson HL chemistry book 3rd edition, Hodder chemistry book 3rd edition ,
Oxford course companion 2023 edition , thinkib.net
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Guiding question: What are the challenges of using
chemical energy to address our energy needs?
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Combustion Reactions
• Combustion reactions are exothermic and are used as energy sources by
society.
• Standard enthalpy of combustion is the enthalpy evolved when one
mole of the substance in its standard state combusts completely in
oxygen under standard conditions.
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A combustion reaction:
• Reaction with oxygen
• Exothermic, so release heat
• Usually needs a spark/ a source of ignition
• Produces a flame
• Reaction is spontaneous when source of ignition is removed
• Redox reaction (oxidation reduction)
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Combustion of metals
• The combustion of reactive metals in the presence of oxygen results
in the oxidation of the metal, the reduction of oxygen, and the
formation of an ionic compound.
• This type of reaction is therefore known as a redox reaction.
• Oxidation can be defined as a gain of oxygen or a loss of electrons.
Reduction is defined as a loss of oxygen or a gain of electrons.
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Combustion of non-metals
• Non-metals are also oxidized when combusted in oxygen, forming non-metal
oxides:
• Sulfur, a non-metal, can be found as impurities in fossil fuels, such as coal and
crude oil. Coal may contain up to 3% of sulfur.
Different oxides may be formed since some non-metals have variable oxidation
states
• Sulfur trioxide reacts with water in the atmosphere, to form sulfuric acid.
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Combustion of organic compounds (hydrocarbons and alcohols)
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Complete combustion
• The reaction of an organic fuel with a plentiful supply of oxygen to produce carbon dioxide
and water.
• Butane is one of the constituents of bottled gas
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Incomplete combustion of organic compound
• Hydrocarbon(organic compounds containing carbon and hydrogen only ).
• If oxygen supply is limited (LR) or high carbon content , incomplete
combustion will occur .
• Less heat evolved
• Carbon monoxide and carbon(soot ) may be produced.
• Possible equations for incomplete combustion of propane
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Combustion of organic compounds (hydrocarbons and alcohols)
Complete Incomplete
• Excess oxygen • Limited oxygen (oxygen is LR) or
• Products: H2O, CO2 fuels with a high % of carbon
• More exothermic • Products: H2O, CO, C (soot)
• Cleaner flame (blue) • More harmful to health and
environment as CO is toxic and
soot is a pollutant
• Less exothermic
• Dirtier flame (orange)
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Combustion of organic compounds (hydrocarbons and alcohols)
Exercise:
Calculate the % of carbon in C6H12 and in CH3C6H5 and predict which
has the sootiest flame
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Why do larger hydrocarbons have a greater
tendency to undergo incomplete combustion?
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• Larger hydrocarbons, and those with aromatic rings, are more likely to
undergo incomplete combustion.
• Which produces a smaller amount of heat energy per unit mass of the fuel
when compared to the complete combustion of the same hydrocarbon.
• Larger hydrocarbons have a reduced volatility due to stronger London
(dispersion) forces (LDFs).
• This affects the way the hydrocarbon molecules interact with the oxygen
molecules and the type of combustion that occurs.
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Energy
• Societies are completely dependent on energy resources
• Some of the uses of energy include:
Transportation
Electricity
Domestic use (internal production
combustion engine)
Industrial facilities Food production
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Energy
There are two main types of energy sources:
Non-renewable sources Renewable energy sources
These are finite energy sources These are naturally replenished
(they run out), such as: (replenished at a rate faster than
• Coal it is used), such as:
• Natural gas Fossil fuels • Solar energy
• Crude oil • Wind energy
• Geothermal energy
• Biofuels
• Hydropower
• Tidal energy
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• The choice of fuel depends on many factors such as:
• Specific energy
• Impact on environment
• Cost
• Availability (reserves)
• Ease of extraction
• Ease of storage and transport
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Fossil Fuels
• When fuels are burned, energy is released in the form of heat
• Specific energy is a useful measure of the quality of a fuel and is used to compare
different fuels
• SE is a positive value
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• Wood (renewable)
has the lowest SE
• Nuclear fuels (such
as uranium) have
the highest SE
Oxford 2023
05/09/2024 Chemistry IBDP 20
Fossil Fuels
Exercise:
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Fossil Fuels
05/09/2024 Chemistry IBDP 22
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Fossil Fuels
Fossil fuels is the name given to a set of energy-rich combustible hydrocarbon compounds
which have been formed from organic remains over millions of years.
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Fossil Fuels
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Fossil Fuels
Natural gas is formed in the same way as crude oil, and hence these two fossil fuels
are often found together.
Natural gas is the cleanest of the fossil fuels because it can easily be treated to
remove impurities, and its combustion is usually complete.
05/09/2024 Chemistry IBDP 26
Fossil Fuels
• Advantages: • Disadvantages
• Produce greenhouse gases that
• High specific heat cause global warming
• Cheap to extract • Non-renewable
• Oil can be easily stored and • Natural gas is difficult to store and
transported in pipelines must be liquified
• Coal and oil produce sulfur dioxide
when burnt which leads to acid
rain
• Natural gas may leak during
transportation so high risk of
explosion
05/09/2024 Chemistry IBDP 27
Fossil Fuels
• Calculating amount of carbon dioxide produced:
Exercise:
Calculate the mass of CO2 produced, in g, per gram of the following
fuels burnt:
(a) Coal
(b) Natural gas
(c) Petroleum (gasoline)
Assume that coal is pure carbon, natural gas is pure methane and
petroleum is pure octane (C8H18) and that combustion is complete
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Fossil Fuels
Answer:
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Fossil Fuels
• Calculating amount of carbon dioxide produced:
Exercise:
Calculate the mass of CO2 produced, in g, per kJ of energy released of
the following fuels burnt, using section 14 of DB:
(a) Coal
(b) Natural gas
(c) Petroleum (gasoline)
Assume that coal is pure carbon, natural gas is pure methane and
petroleum is pure octane (C8H18) and that combustion is complete
05/09/2024 Chemistry IBDP 30
Fossil Fuels
Answer:
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Fossil Fuels
Exercise:
Compare the specific energy (kJ/g) of the following using section 14 of
DB:
(a) Coal
(b) Natural gas
(c) Petroleum (gasoline)
Assume that coal is pure carbon, natural gas is pure methane and
petroleum is pure octane (C8H18) and that combustion is complete
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Fossil Fuels
Answer:
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Fossil Fuels
Exercise:
Oxford p.432, Q4
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Fossil Fuels
Carbon footprint
• Carbon footprint is the total amount of greenhouse gases produced
during human activities.
• Expressed in equivalent tonnes of carbon dioxide.
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Fossil Fuels
Exercise:
Calculate the carbon footprint in tonnes of carbon dioxide of burning
(a) 1 tonne (1000 kg) of octane
(b) 1 tonne of coal, assuming it contains 90% carbon by mass
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Answer
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Fossil Fuels
Pearson 2023
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Green house Effect
• One consequence of the use of
fossil fuels is the release of large
quantities of carbon dioxide, a
product of the combustion
reaction, into the atmosphere.
• Carbon dioxide is a greenhouse
gas, which means it absorbs and
re-radiate IR .
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
• Other greenhouse gases include: nitrous oxide (N2O),
hydroflourocarbons (HFC), perflourocarbons (PFC), CFCs,
ozone and sulfur hexafluoride (SF6)
• These gases have the potential to cause much greater global
warming, but their concentration in the atmosphere is very
low, thus their contribution towards global warming is very low
• On the other hand, CO2 has a greater influence on global
warming because even though it does not absorb much IR
radiation, its concentration is high
05/09/2024 Chemistry IBDP 44
Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Fossil Fuels
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Biofuels
• Biomass: material of plant or animal origin used as fuel
https://www.istockphoto.com
05/09/2024 Chemistry IBDP 52
Biofuels
• Biofuel is a fuel produced from organic matter obtained from plants
or from waste material of plant or animal origin
• Biofuels are renewable sources of energy
• Biofuels are produced from the biological fixation of carbon over a
short period of time through photosynthesis.
• Photosynthesis is an example of biological fixation of carbon.
• Biological Carbon fixation represents where photosynthesis transforms
atmospheric carbon dioxide (CO2) into organic substances.
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Biofuels
• Photosynthesis
+2816 kJ/mol glucose
Energy in the form of sunlight is converted by plants into
chemical energy.
Glucose stores chemical energy in its bonds.
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Biofuels
Photosynthesis
• The chlorophyll in plants absorbs light energy from the sun (visible
light)
• The absorbed light energy is converted into chemical energy.
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Biofuels
• Biofuels:
• Bioethanol – substitute for gasoline
• Biodiesel – substitute for diesel
• Biogas – substitute for natural gas
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Biofuels
• Bioethanol:
Energy crops: sugar plants
such as sugar cane, sugar
beet or starch plants such as
corn starch, potatoes, wheat
• The basic reaction that happens during fermentation is the enzyme-catalysed
conversion of glucose to ethanol:
05/09/2024 Chemistry IBDP 57
Biofuels
• Bioethanol can be used in internal combustion engines as a substitute
for gasoline
• The carbon dioxide produced in the fermentation process is balanced
by carbon dioxide taken in for photosynthesis while the plant is
growing, so the fuel can be considered carbon neutral
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Biofuels
• Biodiesel:
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Biofuels
The industrial production of biofuels in many countries has economic and environmental implications.
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Biofuels
• Advantages: • Disadvantages:
• Renewable resource • Uses agricultural resources, land
and water resulting in increased
• Reduced greenhouse food prices on a global scale
emissions and less polluting
• High cost of production
than fossil fuels
• Lower specific energy than fossil
• Decreases a country’s fuels
dependence on oil • Deforestation to produce land for
growing biofuels
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