Energy Flashcards
1
Q
Why is coal considered a form of high quality energy?
A
When coal burns, large amounts of heat energy are released
2
Q
Why is steam considered a form of low-quality energy?
A
This is energy lost to the environment and does not do much work.
3
Q
What law of thermodynamics is efficiency based on?
A
The first law of thermodynamics: energy can not be created or destroyed
4
Q
What are the changes in a coal-fired power station?
A
chemical potential energy => heat energy => Kinetic energy => Electrical energy
5
Q
what percentage of efficiency is a coal-fired power station; approximately?
A
35% - 40%
6
Q
A gas-fired power station has an energy output of 1.75 × 1025 J. The input energy required to produce this amount of energy is 3.65 × 1025 J. Calculate the percentage efficiency of the power station.
A
Efficiency = (1.75 × 10^25 / 3.65 × 10^25) × 100
Efficiency = 47.9%
7
Q
What is energy density and its units?
A
- This is the energy stored per unit volume.
- the SI unit for energy density is J/m^3
8
Q
What information does energy density provide about a fuel?
A
The higher the energy density of a fuel, the more energy can be stored per unit volume
9
Q
What is the energy density of gases compared to other states for the same conditions?
A
Gases tend to have lower energy densities than liquid or solid fuels s they take up a greater volume under same conditions
10
Q
What is specific energy and its SI units?
A
- This is the energy produced per unit mass
- The SI unit for specific energy is given as J/kg
11
Q
Calculate the specific energy of butane (C4H10) using sections 1, 6 and 13 of the IB data booklet.
A
1) Use section 13 to determine the enthalpy of combustion (ΔHc) value for butane, in kJ kg-1.
According to section 13, the ΔHc for butane = -2878 kJ mol-1
2) Use the equation in section 1 to calculate the specific energy.
Specific energy = energy released from fuel/mass of fuel consumed
The ΔHc value is for the combustion of one mole of a compound, therefore divide the ΔHc by the molar mass of the compound (using section 6 to calculate the molar mass of C4H10).
Specific energy of C4H10 = 2878 / (58.14 /1000) = 4.950 × 104 kJ kg-1
12
Q
what are renewable energy sources?
A
- These are energy sources that are naturally replenished on a human timescale
13
Q
What are the advantages of renewable energy sources?
A
They are less polluting than non-renewable energy sources
14
Q
Why are renewable energy sources limited?
A
Due to factors such as cost and availability of the renewable energy source
15
Q
Provide examples of renewable sources of energy?
A
- Solar
- Tidal
- Geothermal
- Biomass
- Wind
- Hydroelectric
16
Q
How does solar power work, and what are the advantages and disadvantages of this energy source?
A
- Used to convert the light energy from the Sun into Electrical energy
- Advantages: Little negative disadvantages to the environment
- Disadvantages: Only generated during daylight hours and the Sun’s energy is available in a very dispersed form, meaning large areas of land must be covered by solar panels
17
Q
What is tidal energy, and what are the advantages and disadvantages of this energy source?
A
- Energy is generated by tidal waves in the oceans and seas as a result of the moon’s gravitational pull on the water; kinetic energy is transformed to electrical energy
- Advantages: Has high efficiency and a long working life
- Disadvantages: Causing disruption to migrating fish; can only occur twice a day meaning that electricity can only be generated for about ten hours a day
18
Q
What is geothermal energy and how does it work?
A
- Type of energy stored within the Earth; originates from radioactive decay happening at Earth’s core
- Heat is radiated outward the Earth’s crus where it is used to heat water; the steam is used to heat buildings or generate electricity.
19
Q
What is biomass energy, and what are the advantages and disadvantages of this energy source?
A
- it is organic material storing chemical energy that originates from the photosynthesis of plants; includes wood and sugar cane
- Biomass, unlike fossil fuel can be grown in a relatively short time.
- Sugar cane is converted to ethanol which is added to petrol to form gasohol
- Advantages: it is carbon neutral
20
Q
How does wind power work, and provide the advantages and disadvantages of of this source of power?
A
- wind converts the kinetic energy of the wind into electrical energy through turbines
- Advantage: wind power emits no carbon dioxide
- Disadvantage: Electricity is only generated when the wind is blowing
21
Q
How does hydroelectric energy work, and what are the advantages and the disadvantages of this source of energy?
A
- Converts gravitational potential energy of water to electrical energy
- Advantages: no greenhouse gases are produced and it is relatively cheap
- Disadvantages: large areas of land are flooded to create a reservoir behind the dam
22
Q
How are the non-renewable sources, fossil fuels formed
A
Ancient plants absorbed energy from the Sun during photosynthesis, producing glucose, a biological compound with the molecular formula C6H12O6. The reduction of biological compounds that contained carbon, hydrogen, nitrogen, sulfur and oxygen led to the formation of coal, oil and natural gas.
23
Q
Describe the formation of coal.
A
- formed from the remains of prehistoric plants
- When the plants died, they became buried under layers of mud and sand.
-Over millions of years, heat and pressure, combined with the anaerobic conditions, converted the decaying plant material into coal
24
Q
What do the different types of coal formed depend on?
A
- depending on the time and pressure they were subjected to
25
What is lignite coal?
- it is a soft brown coal with a lower specific energy formed from compressed peat
26
What is bituminous coal?
coal that has a higher specific energy than lignite due to the extra pressure exerted upon it
27
What is anthracite coal?
- coal that has the highest carbon content, the lowest amount of impurities and the highest specific energy of all the types of coal.
28
How does the formation of oil and natural gas occur? (4)
- Oil and natural gas were formed from ocean-dwelling plants and animals
- When these organisms died, they sank to the bottom and became buried under layers of sediment
- As the layers of sediment increased, the heat and pressure also increased and combined with anaerobic conditions, produced oil and natural gas
- The oil and natural gas migrated through porous rock until they reached impermeable layers of rock, where they remained trapped for millions of years.
29
Write down the equation for the combustion of methane.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
30
What are the advantages of natural gas (4)
- Natural gas is a relatively clean fuel.
- Natural gas has a higher specific energy than coal and oil.
- Natural gas has CNG that allows it be compressed or liquefied for ease of transport.
- Natural gas does not contribute to acid deposition.
31
What are the disadvantages of natural gas?
- As with all fossil fuels, natural gas is a non-renewable energy source.
- When burned, natural gas produces CO2, a potent greenhouse gas.
- Natural gas has a lower energy density than coal and oil.
- Natural gas is unevenly distributed throughout the world.
32
What are the advantages of coal?
- Coal is relatively inexpensive.
- Coal has a high specific energy and energy density.
- Coal can be converted into liquid fuels.
- Coal is distributed throughout the world.
33
What are the disadvantages of coal?
- As with all fossil fuels, coal is a non-renewable energy source.
- When burned, coal produces CO2, a potent greenhouse gas.
- The combustion of coal that contains sulfur produces acid deposition.
- The mining of coal can cause environmental damage.
34
What are the advantages of crude oil?
- Petroleum products are relatively inexpensive.
- Petroleum products have high specific energies and energy densities.
- Petroleum products (such as petrol) are easily transported.
- Crude oil is a valuable feedstock for petrochemicals such as fertilisers.
35
What are the disadvantages of crude oil?
- As with all fossil fuels, crude oil is a non-renewable energy source.
- When burned, petroleum products produce CO2, a potent greenhouse gas.
- Drilling for and transporting crude oil can cause environmental damage.
- Crude oil is unevenly distributed throughout the world.
36
How does the percentage of higher boiling point fractions compare to the percentage of lower boiling point fractions in crude oil.
- Higher percentage of higher boiling point fractions
- Lower percentage of lower boiling point fractions
37
Crude oil separated in a process called?
Fractional distillation
38
How does the separation of crude oil work? (5)
- Crude oil is heated to about 400°C
- The highest temperature is at the bottom of the column and lowest at the top
- The different fractions are vaporised and rise up the distillation column
- The level at which the fractions condense depends on the boiling point
- Smaller more volatile hydrocarbons rise to the top of the column and larger, less volatile hydrocarbons collect at the bottom
39
What does the boiling points of hydrocarbons depend on?
molar masses and strength of the intermolecular forces between the molecule
40
How do molecules that have lower molar masses compare to those with higher molar masses in terms of volatilty?
- high volatility for those with lower molar masses
- low volatility for those with higher molar masses
41
Why do larger hydrocarbons have less volatility and high boiling points?
- London forces between the molecules are stronger
42
Provide a list of fractions (8) from crude oil and their uses?
Refinery gas - Fuel, feedstock for petrochemicals
Petrol - Fuel for cars
Naphtha - Production of organic chemicals, converted to petrol
Kerosene - Jet fuel, domestic heating
Diesel fuel - Fuel for trucks and agricultural machinery
Lubricating motor oil - Lubricating oil, waxes and polishes
Fuel oil - Fuel for ships and power stations
Residue - Bitumen for roads ( used to make asphalt)
43
What is carbon footprint?
- It is defined as the total amount of greenhouse gases produced to directly and indirectly support human activities, expressed in equivalent tonnes of carbon dioxide (CO2).
44
Name other sources of CO2 emission apart from the combustion of fossil fuels?
- production of food, goods and materials
45
How can the carbon footprint of a person be reduced?
- Using public transport
- Walking
- Cycling
- Buying locally grown food
- Switching off lights or heating in the home when out of use
46
Why is Carbon footprint difficult to calculate?
1. It is difficult to decide which specific carbon-based greenhouse gases to include in the calculation and whether or not non-carbon based greenhouse gases should be included.
2. Whether or not carbon monoxide (CO) from incomplete combustion should be included, as it can be oxidised to form carbon dioxide.
3. Lastly, the difficulty in summing up the steps in a process that results in the production of carbon dioxide.
47
Calculate the mass of CO2 produced by the combustion of 1.00 × 106 kg (1000 tonnes) of anthracite coal (assume that anthracite is 80% carbon by mass).
1. Start by writing a balanced equation for the reaction.
C(s) + O2(g) → CO2(g)
2. Convert from mass of carbon to amount of mol of carbon.
Assume that anthracite coal is 80% carbon:
80% × 1.00 × 10^6 kg = 8.00 × 10^5 kg C = 8.00 × 10^8 g C
amount in mol (n) = mass in grams (m) / molar mass (M)
(n)C = 8.00 × 108 g / 12.01 gmol-1 = 6.66 × 10^7 mol
3. Determine the molar ratio of carbon to carbon dioxide.
From the balanced equation, we can see it is a 1:1 ratio.
4. Multiply the amount in mol of carbon by 1.
6.66 × 10^7 mol × 1 = 6.66 × 10^7 mol CO2
5. Convert from amount in mol of CO2 to mass of CO2.
mass in grams (m) = amount in mol (n) x molar mass (M)
mass of CO2 = 6.66 × 10^7 × 44.01 = 2.93 × 10^9 g
6. Convert to kg by dividing by 1000.
2.93 × 10^9 g / 1000 = 2.93 × 10^6 kg CO2 = 2.93 × 10^3 tonnes CO2
48
Calculate the mass of CO2 produced by the combustion of 5.00 × 104 kg of butane (C4H10)
1. Start by writing a balanced equation for the reaction.
2C4H10(g) +13O2(g) → 10H2O(l) + 8CO2(g)
2. Convert from mass of butane to amount in mol of butane.
amount in mol (n) = mass in grams (m) / molar mass (M)
(n)C4H10 = 5.00 × 10^7 / 58.12 = 8.60 × 10^5mol
3. Determine the molar ratio of butane to carbon dioxide.
From the balanced equation, we can see it is a 2:8 or 1:4 ratio.
4. Multiply the amount in mol of butane by 4.
8.60 × 10^5 × 4 = 3.44 × 10^6 mol CO2
5. Convert from amount in mol of CO2 to mass of CO2
mass in grams (m) = amount in mol (n) × molar mass (M)
mass of CO2 = 3.44 × 10^6 × 44.01 = 1.51 × 10^8 g
6. Convert to kg by dividing by 1000
1.51 × 10^8 g / 1000 = 1.51 × 10^5 kg CO2 = 151 tonnes CO2
49
What can coal gas and coal liquid be used to do?
- Coal gas => Provide street lighting
- Coal liquid => To produce liquid fuels
50
What is coal gasification and Syngas?
-This is the process of converting coal into syngas or synthetic natural gas (CH4)
- Syngas is a mixture of carbon monoxide (CO) and hydrogen gas (H2). It can be produced from natural gas, coal, biomass and oil
51
What are the uses and benefits of coal gasificaiton?
- Benefit: Coal gasification has lower SOx and NOx emissions and particulate emissions from burning coal-derived gases.
- Use: it is useful as an intermediate for the production of compounds such as methanol and ammonia
52
What process is used to convert coal to liquid hydrocarbons?
- Via the Fischer-Tropsch process
53
Provide an example equation of the conversion of coal to syngas ?
C(s) + H2O(g) → CO(g) + H2(g)
54
Provide an example equation of the conversion of syngas to synthetic natural gas (CH4).
CO(g) + 3H2(g) → CH4(g) + H2O(g)
55
Provide a direct process equation of converting coal to synthetic natural gas .
2C(s) + 2H2O(g) → CH4(g) + CO2(g)
56
What is the end goal of coal gasification, and how is this achieved?
- To transform coal to synthetic natural gas or syngas
- By either reacting coal to obtain syngas then to synthetic natural gas, or reacting coal with vapour to obtain direct synthetic natural gas.
57
How many types of coal liquefaction are there and what is it?
- Coal liquefaction is the process of converting coal into liquid hydrocarbons for fuels
- There is direct and indirect coal liquefaction processes
58
Provide the general equation for the direct liquefaction of coal and conditions required to carry out this process.
- General equation: nC(s) + (n+1)H2(g) →
CnH2n+2(l)
- Conditions: presence of heat and catalyst
59
Explain the indirect process for coal liquefaction and provide a general equation?
- Coal is first converted to syngas then into a liquid hydrocarbon via Fischer-Tropsch process
- General equation: nCO(g) + (2n+1)H2(g) → CnH2n+2(l) + nH2O
60
What is causes knocking and what is it in an engine?
- This is when in a car engine premature ignition of air and fuel mixture occurs. AKA autoignition
61
What are the disadvantages of knocking in an engine?
- Causes the engine to lose power and can therefore result in engine damage
62
What is an octane number?
- This is a measure of the fuel's ability to resist auto-ignition
- The higher the octane number, the greater the resistance to auto-ignition
63
What octane numbers have been assigned to C7H16, Heptane and 2,2,4-trimethylpentane (iso-octane)?
- Heptane => zero, a greater tendency to auto-ignite and cause knocking
- Iso-octane => hundred, less tendency to auto-ignite
64
Compare a fuel with an octane rating of 93 to iso-octane and heptane.
This fuel has a tendency to auto-ignite as a mixture of 93% 2,2,4-trimethylpentane and 7% heptane
65
Provide the octane numbers of methylbenzene, cyclohexane and butane.
- Methylbenzene (C6H5CH3) - RON [121]
- Cyclohexane (C6H12) - RON [83]
- Butane (C4H10) - RON [94]
66
What are the benefits of straight-chain, cyclic and aromatic hydrocarbons?
They have a lower tendency to auto-ignite, thus have higher octane numbers
67
What chemical processes are used in petrochemical industries to increase the octane rating of fuels.
- Catalytic reforming - it involves aromatisation and isomerisation and it converts straight-chain into branched or aromatic hydrocarbons
- Cracking - breaks long-chain into shorter chain hydrocarbons
68
What is catalytic reforming?
- It is a chemical process that converts low-octane hydrocarbons into higher-octane hydrocarbons called reformates
69
What is aromatisation? (2)
- It is a process that converts naphtha, which is composed mainly of straight-chain hydrocarbons (with between 6 and 10 carbon atoms), into aromatic hydrocarbons.
- Aromatic hydrocarbons have higher octane numbers and a lower tendency to auto-ignite and cause knocking
70
Under what conditions is hexane catalytically reformed to produce benzene and hydrogen.
- Catalyst - platinum (Pt)
- Temperature and pressure - 500ºC and a pressure of 20 atm
71
Provide the aromatisation of hexane.
C6H14 → C6H6 + 4H2
72
What is isomerisation?
-This is a form of catalytic reforming which converts straight-chain hydrocarbons with low octane numbers into branched-chain hydrocarbons.
- Branched-chain isomers have a higher resistance to auto-ignition, thus used to increase the octane rating of petrol (gasoline)
73
Provide an example of a methane molecule being isomerised?
Hexane => 2,2-dimethylbutane, which increases the octane rating
74
What is cracking?
- This involves taking long-chain hydrocarbons and breaking them up into short-chain hydrocarbons.
- It takes the high percentage of less useful long-chain hydrocarbons and converts them into the more desired short-chain hydrocarbons
75
Provide the equation for the breaking of heptane into pentane and ethene?
C7H16 → C5H12 + C2H4
76
What the typical conditions for cracking?
- Heating of reactants in the presence of a zeolite catalyst
77
What is binding energy?
-This is the energy required to split the nucleus into its constituents particles.
- This is the energy released when the nucleus is formed or the energy required to split it again
78
How does the binding energy per nucleon compare to the stability of the nucleus?
- The greater the binding energy per nucleon, the more stable the nucleus
79
What is the most stable part of a graph showing the binding energy per nucleon against nucleon number?
- Nuclei with mass numbers around 60
- Fe-56 and Ni-62 have the highest binding energy per nucleon thus the most stable
80
Define fusion and fission with respect to an average binding energy per nucleon against number of nucleons graph, and the results of these reactions.
- Fusion- This is the splitting of a nucleus which increases the binding energy per nucleon=> it happens to the right of the most stable nuclei on the graph
- Fission- This is the binding of two nuclei, providing higher binding energy per nucleon=> happens to the left of the most stable nuclei on the graph
81
What is nuclear fusion?
This is the binding of smaller nuclei to make a larger one
82
Why is nuclear fusion not possible on Earth?
- Because scientists have great difficulty in replicating the conditions that enable nuclear fusion to take place in the core of the Sun, on Earth.
83
What advantage does nuclear fusion have over nuclear fission?
- Higher specific energy than nuclear fission
- Produces less radioactive waste
- More abundant
- Cheap fuel source
- Cannot produce products such as plutonium to make nuclear weapons
84
Atomic spectrum in the Sun: Compare the spectrum between the photosphere of the (cooler atmosphere of the sun) and the sun's interior?
- A continuous spectrum is produced in the sun's hot interior
- An absorption spectrum is produced in the cooler atmosphere of the sun
85
From the absorption spectrum of the sun, what can be deduced?
That the sun is mostly comprised of hydrogen
86
In an emission spectrum, in which direction is the wavelength increasing?
From left to right
87
What is the relationship between energy, wavelength and frequency?
- The higher the energy, the higher the frequency and the shorter the wavelength.
88
From what main energy level is the energy absorbed by electron transitions correspond to the wavelength and frequency of visible light.
From the second main energy level (n=2) to any of the other transitions in the higher levels
89
What is nuclear fission?
This is the process of a large unstable nucleus splitting into smaller, more stable nuclei the binding energy per nucleon increases
90
For nuclear fission to happen, what is done?
- The large nucleus is bombarded with a neutron to form smaller nuclei
91
What is a self-sustaining nuclear chain reaction?
- This is when at least an additional fission is initiated by a neutron
92
What happens in chain reactions?
- The neutron is captured by the nucleus of the large element, which undergoes fission and releases many more neutrons which cause further fission
93
What is critical mass?
- This is the minimum mass of fuel required for a nuclear fission reaction to be self-sustaining
94
What is the difference between U-235 and U-238?
- U-235 is a fissile isotope meaning it is capable of sustaining a nuclear chain reaction
- U-238 is a fissionable but not fissile isotope despite being abundant- meaning that it is not capable of sustaining nuclear chain reaction
95
What is a breeder reactor?
- This is a nuclear reactor that generates more fissile material than it consumes
96
Why were fast breeder reactors developed?
This is because of the limited supply of the fissile U-235
97
What is the problem with U-238 in relation to being fissile?
- It the most abundant isotope yet it is not fissile
- That is why it needs to be converted to U-235 which is less abundant, but very fissile
98
Write the reactions that take place in a fast breeder reactor to convert non-fissile U-238 to fissile Pu-239.
1. U-238 undergoes neutron capture to form U-239:
U-238 + n-1 => U-239
2. U-239- 92 undergoes beta minus decay to form Np -239-93:
U-239-92 => Np-239-93 + e-0- (-1)
3. Np-239-93 undergoes beta minus decay to form Pu-239-94:
Np-239-93 => Pu-239-94 + e-0-(-1)
99
Write the equation for Pu-239 as it undergoes a nuclear reaction by being bombarded with a neutron.
- Pu-239-94 + n-0-(-1) => Ba-142-56 + Sr- 93 -38 + 2 n-0-1
- the bombarded element is fissile therefore can sustain a nuclear chain reaction
100
Why are the use of fast-breeder reactors less scoped?
- Costs for a breeder reactor are about 25% higher than light-water reactors
- They can be used to create weapons using plutonium which is also highly toxic
101
What is low-level radioactive waste?
- This are protective clothing and paper towels that have been in proximity to radioactivity
- The isotopes have generally low activity and short half-lives
102
Provide examples of sources of low-level waste and how they can be stored or disposed
- Hospitals and Research laboratories
- They can be stored until the isotopes decay and then disposed in landfill sites or incinerated
103
What are intermediate level radioactive waste?
Composed of longer-lived isotopes than low-level waste.
104
What are the sources of intermediate level waste and how are they stored or disposed?
- ion-exchange resins and radiation therapy
- Can be disposed of by burying it in shallow repositories
105
What are high level waste?
- Composed of highly radioactive material such as spend fuel rods
- They tend to have a high activity and long half-life, thus must be stored for long periods of time
106
Provide methods of storage and disposal.
- Spent fuel rods are removed from the reactor core and stored in cooling ponds; the water is used to shield the radiation and also cooling due to the heat release from the spent fuel rod
- Disposal involves vitrification, which is just the encasing of the waste in glass and storing it deep underground. The chosen location of must be geologically stable to prevent possibility of leakage.
107
What is half-life?
This the time taken for half the atoms in a sample to decay.
108
What is binding energy?
It is the energy required to disassemble a nucleus into its component nucleons.
109
Given that an atomic nucleus' mass is slightly less than the mass of the nucleons that make up the nucleus, what is this mass difference equal to?
Binding energy of the nucleus
110
What produces the energy released during a nuclear fission and fusion reaction?
- It is as a result of a small amount of the mass being directly converted into energy.
111
In fission what mass is smaller; the constituent nucleons or the parent nucleus?
- The resultant constituent nucleon
112
In a fusion reaction, what mass is less, the nucleus formed or the nuclei that fused together?
The mass of the nucleus is less than the mass of the fused together nucleus
113
What is the relationship between the the amount of binding energy and stability of nucleus?
- The higher the binding energy, the more stable the nucleus
114
What is the most stable isotope?
Fe-56
115
Why is it hopeful that nuclear fusion could be possible on earth?
This is because in nuclear fusion reactions the difference in energy between reactants and products is significantly more than in fission reactions.
116
How can the binding energy per nucleon of a nucleus be increased?
Through nuclear fusion and fission
117
What are photosynthetic autotrophs?
- These are organisms that are able to produce complex organic molecules using energy from the sun.
118
What are the energy transformations in photosynthesis?
Light energy from the sun is converted into chemical energy
119
What other use does the glucose produced by plants during photosynthesis have ?
- This glucose can be converted to ethanol, which can be blended with petrol or burned directly in car engines
120
Provide redox half-equations and the overall equation for photosynthesis.
Reduction of carbon dioxide: 6CO2 + 24H+ + 24e- → C6H12O6 + 6H2O
Oxidation of water: 12H2O → 6O2 + 24H+ + 24e-
Addition of both results in:
6CO2 + 6H2O → C6H12O6 + 6O2
121
How is sunlight absorbed in green plants?
- By a biological pigment: Chlorophyll
121
What is the part of the chlorophyll that is responsible for absorbing visible light?
- An extended conjugated system of many alternating single and double bonds
122
What is the metal ion in chlorophyll, the R group in chlorophyll a, and the functional group in chlorophyll b?
- Metal ion: Magnesium ion (Mg-2+)
- Functional group in chlorophyll a: methyl group (CH4)
- Functional group in chlorophyll b: aldehyde group (CHO)
123
In what region of the electromagnetic spectrum are pigment molecules capable of absorbing light?
in the visible region => wavelength; 400nm to 700nm
124
Why does chlorophyll appear green?
- Because it absorbs wavelengths of light that correspond to blue and red light and reflects the remaining wavelengths, making it appear green
125
Explain how energy is absorbed in terms of electrons in extensive conjugated systems of pigment molecules.
- Since pigment molecules have delocalised electrons, they are free to move
- Thus when electrons become excited by sunlight they transition to higher energy levels
- The energy absorbed when the electrons transition to higher energy levels correspond to the wavelengths of visible light
126
What is beta-carotene?
- This is biological pigment. It is a red-orange pigment responsible for the orange colour of carrots and pumpkins
- It also has an extensive conjugated system that allows it to absorb light in the visible region
127
Where is the energy in biofuels obtained from/
- From biological carbon fixation
128
What is carbon fixation?
- This is a process that takes inorganic carbon (CO2) and converts it into organic compounds such as glucose (C6H12O6)
129
For what reason is it that biofuels, in theory, are carbon neutral?
- It is because the carbon dioxide that is released when biofuels are used is the same that is absorbed during photosynthesis
130
Why is it that in reality biofuels are not completely carbon neutral?
- This is because fossil fuels are used to fuel the farm machinery and to make fertilisers that are necessary to grow the crops.
- While they are not completely carbon neutral, they add less carbon dioxide to the atmosphere than the use of fossil fuels such as coal, oil or natural gas
131
What process is used to convert glucose to ethanol/ bioethanol? Under what conditions and what plants are fermented?
- Fermentation
- Which converts sugars such as glucose into ethanol in the presence of yeast and bacteria- Catalysed by the enzyme; Zymase- Temperature: 37º C without oxygen
- Starchy plants such as corn, wheat or barley or potatoes
132
Provide the equation for the fermentation of glucose to ethanol.
C6H12O6 → 2C2H5OH + 2CO2
133
Since ethanol produced in fermentation is blended with petrol in varying volumes, the mixtures of ethanol and petrol are given names beginning with 'E'. What does E10, for example mean?
This is fuel containing 10% by volume of ethanol and 90% by volume of petrol
133
From what sources is biodiesel, a biofuel, formed from?
vegetable oil, fish oil, animal fats and waste cooking oil
134
What is the name of the lipids composed of these oils?
- They are called triglycerides; which consist of glycerol backbone bonded to three fatty acids.
- (The fatty acid can be the same or different)
135
Why is it that vegetable oils can not be used in unmodified diesel engines even with a similar energy content as that of regular diesel fuel? (2)
- They are too viscous; resulting from their higher molar masses and intermolecular forced that exist between the fatty acid chains of the triglycerides
- Vegetable oils are also less volatile than regular diesel, given that they are more difficult to ignite and often undergo incomplete combustion (this can result in engine damage)
136
Due to viscous nature of vegetable oils, they are chemically modified in a transesterification reaction. What is a transesterification reaction?
- This is where a triglyceride is reacted with a short-chain alcohol. The alcohol can either be ethanol or methanol => resulting int glycerol and (alkyl esters, known as biodiesel)
137
What catalysts are used in transesterification reaction?
- Strong base (NaOH) or Strong acid (HCl)
138
Since the reaction is reversible, excess alcohol is used. Why?
- In order to shift equilibrium to the right in favour of products
139
Provide the general equation for a transesterification reaction.
The letter R, represents an alkyl group:
RCOOR1 + R2OH → R1OH + RCOOR2
140
Explain fatty acid methyl ester (FAME) in relation to biodiesel. (3)
- It has similar energy content to vegetable oil but less viscous
- Less viscous because of their lower molar mass resulting in weaker intermolecular forces between molecules
- Lower viscosity allows them to be used in unmodified diesel engines.
140
Provide advantages and disadvantages of ethanol as a biofuel.
Advantages:
- higher octane rating than gasoline
- Renewable source of energy
- produces less carbon monoxide (CO) than gasoline when burned in car engines
- Economically viable for countries with low reserves of crude oil
Disadvantages:
- Has lower specific energy than octane
- More volatile, thus evaporates easily
- Land that could be used for crop plantation, is used for bioethanol instead
141
What are advantages and disadvantages of biodiesel?
Advantages:
- it is renewable
- Theoretically carbon neutral
- It is non-toxic and biodegradable
- Reduces emissions of atmospheric pollutants such as carbon dioxide and sulphur dioxide
Disadvantages:
- Land that could be used for crop plantation is used instead to produce biodiesel
- Possible loss of biodiversity from the planting the crops used to produce biofuels in general
142
What is the difference of reacting a triglyceride with methanol or ethanol?
- Methanol: a methyl ester, glycerol and fatty acids
- Ethanol : an ethyl ester, glycerol and fatty acids
143
What is the greenhouse effect?
This is the name given to the process that warms the surface of the Earth. This is more correctly called the natural greenhouse effect.
144
How does the greenhouse effect work?
- The sun radiates short wavelength radiation (UV and visible light)
- The greenhouse gases in the atmosphere are transparent and allow the passage of incoming short wavelength solar radiation
- The Earth's surface reradiates some of this radiation back into the atmosphere as longer wavelength radiation (infrared)
- The greenhouse gases in the atmosphere absorb this longer wavelength radiation and reradiate it back to the surface of the Earth, causing a temperature increase at the surface
145
Provide examples of greenhouse gases, their source, their greenhouse factor and Relative abundance.
- H2O => Evaporation from oceans and lakes=> 0.1 => 0.10
- CO2 => Combustion of fossil fuels such as coal and natural gas=> 1 => 0.036
- CH4 => Anaerobic decay of organic matter by livestock =>30 => 0.0017
146
Compare the greenhouse factor and Relative abundance of H2O, CO2 and CH4?
- The greenhouse factor is given relative to CO2 which has a greenhouse factor of 1
- CH4 has the greatest greenhouse factor and lowest relative abundance of 0.0017 between the three and the value is 30
- H2O has the greatest relative abundance 0.1 and the least greenhouse factor 0.1 among the three gases
147
What is greenhouse factor?
- This is the measure of a gas's ability to absorb infrared radiation, compared to carbon dioxide
148
What is relative abundance?
- This is measure of how much of the greenhouse gas is present in the atmosphere
149
Explain how a molecule absorbs infrared radiation in terms of its vibrational mode?
- In order for a gas to absorb infrared radiation, there must be a change in the dipole moment of the molecule as the bonds undergo asymmetric stretching and bending
- These vibrational modes that absorb IR radiation are known as being IR active
150
Why can carbon dioxide absorb IR radiation?
- Its vibrational modes have frequencies that correspond to the frequency of infrared radiation and that is why it can absorb electromagnetic radiation in the wavelength range of IR radiation
151
Compare the number of vibrational modes between methane CH4 and carbon dioxide CO2?
- Methane has two active modes: Asymmetric stretching and bending
- Carbon dioxide has three vibrational modes but two IR active modes: symmetric stretching, asymmetric stretching and bending
152
What are the effects of global warming?
- Rising Sea Levels
- Changes in World Food production
- Ocean acidification
153
How does global warming cause rising sea levels?
- Rising sea levels can cause flooding in low-lying regions and a loss of habitats for organisms in coastal wetlands
- There is usually a balance between the melting and accumulation of ice during the winter and the summer seasons
- Global warming however, cause more ice to melt in the summer season and less ice to accumulate during winter, this leads to the rise in sea level
- Another reason is that a rise in temperature cause the ocean's and sea's water to expand and therefore leading to rise in sea levels
154
How could global warming lead to changes in world food production?
- Global warming can lead to increased levels of evaporation resulting in water shortages from lakes and rivers and greater amounts of precipitation
- Both can lead to drought and flooding respectively and therefore have negative impacts on the world food production
- In some other parts of the world it can lead to higher levels of carbon dioxide in the atmosphere available for photosynthesis and warmer temperatures resulting in longer growing seasons. These could lead to an increase in food production
155
Provide examples of reducing carbon dioxide emissions?
-Use of renewable energy sources such as bioethanol and biodiesel which release less CO2 in to the atmosphere; they are carbon neutral
- Increasing energy efficiency and conservation with methods such as switching off electronic devices when not in use, walking or using public transport and increased use of insulation in housing to prevent heat loss
- Capturing CO2 and storing it: This process involves capturing CO2 at its source and transporting it to a suitable location where it is stored underground preventing it from entering the atmosphere. Planting trees can also help absorb CO2 during photosynthesis
156
What is ocean acidification and how does it happen?
- This is the process by which oceans become more acidic. Increasing acidity means increasing hydrogen ion concentration and a decrease in the pH value.
- Concentration of gaseous carbon dioxide dissolves in the world's oceans, rivers and lakes to form carbonic acid
157
Give the reaction of CO2 with water in the oceans to form carbonic acid.
CO2(aq) + H2O(l) ==> H2CO3(aq)
158
Increased acidity can be harmful to organisms such as shellfish and corals. Corals are composed of Calcium carbonate, provide a reaction equation of the destruction of coral.
CaCO3(s) + 2H+(aq) → Ca2+(aq) + CO2(g) + H2O(l)
159
Provide another way in which acidity can also harm creatures in the ocean that require carbonate ions to produce their shells.
- Hydrogen ions in the water react with carbonate ions to form the hydrogen carbonate ion (HCO3-).
- This reaction reduces the availability of carbonate ions in the ocean water, affecting the ability of marine organisms to produce their shells.
160
How does Le Chatelier's principle explain how ocean acidity is increased.
=> Consider the following reactions
(1) CO2(g) ⇌ CO2(aq)
(2) CO2(aq) + H2O(l) ⇌ H2CO3(aq)
(3) H2CO3(aq) ⇌ H+(aq) + HCO3-(aq)
When the concentration of gaseous carbon dioxide increases, a shift to the right in the equilibrium happens and forms a chain reaction effect finally resulting in carbonic acid increasing and shifting equilibrium towards the right where hydrogen ions increase and finally result in increased acidity and lower pH.
161
Explain global dimming?
- It is caused by the decreasing amount of solar radiation reaching the Earth's surface as a result of particulates in the atmosphere such as oxides of sulphur, ash and soot absorb and reflect incoming solar radiation from the sun back into space.
- Global dimming is also caused by polluted clouds which are clouds that contain more water droplets than unpolluted clouds. These clouds have increased reflectivity which causes an increase in the amount of solar radiation reflected back into space
162
What are the impacts of global dimming?
- Resulted in cooling of water in the oceans which led to a lower rate of evaporation, which in turn results in lower amounts of precipitation
- This has potential to cause drought as there is no rain water following lower precipitation amounts
- Global dimming is also through to be hiding the true effects of global warming and reducing global dimming could actually cause an increase in global warming
