Topic 4 - Managing Resources Flashcards

Question

How is bomb calorimetry set up?

Answer 1

A bomb calorimeter is an insulated vessel designed to measure enthalpy of combustion of solid or liquid fuels. The bomb is pressurised with oxygen gas and the weighed pellet of fuel is combusted via an ignition fuse.

Answer 2

Incomplete combustion of fuels could result in less energy release. Heat released during combustion could be absorbed by other mediums such as the metal and air. The heat release is not instantaneous as some heat may be absorbed by the water, which is further lost by the air over time. Depending on the fuel, evaporation may occur which changes the mass over time.

Answer 3

Combustion of fuels results in a net release of energy, from the formation of covalent bonds between carbon, oxygen and hydrogen in the two complete combustion products. Therefore, it is exothermic and enthalpy is always negative.

Answer 4

Q=m x c x delta T (joules)

Answer 5

Molar enthalpy of combustion represents the quantity of heat released per mole of fuel that undergoes combustion. delta H = m x c x delta T/1000 x n (kJ/mol) delta H = Q/1000 x n (kJ/mol)

Answer 6

c=4.18 (J/g/degrees Celsius)

Answer 7

specific energy = delta H/MW (kJ/g)

Answer 8

energy density = (delta H/MW) x p (kJ/L) where p is density

Answer 9

The comparison of fuels is used to maximise energy output meaning fuels with higher molar enthalpy of combustion, specific energy or energy densities can be considered better fuels.

Answer 10

6CO2 (g) + 6H2O (l) -light/chlorophyll-> C6H12O6 (s) + 6O2 (g) delta H= +2802 kJ/mol carbon dioxide + water -light/chlorophyll-> glucose + oxygen Photosynthesis is the process of generating chemical energy from light energy, carried out by plants and micro-organisms such as plankton, algae and cyanobacteria. It is an endothermic reaction as it absorbs energy from its surroundings (sunlight is absorbed by chlorophyll).

Answer 11

C6H12O6 (s) + 6O2 (g) --> 6CO2 (g) + 6H2O (l) delta H= -2802 kJ/mol glucose + oxygen --> carbon dioxide + water Respiration is carried out by all living things to release chemical energy stored in covalent bonds of carbohydrates and lipids. It is the reverse of photosynthesis, and occurs in the mitochondria of the cell. Respiration is an exothermic process as energy is being released (responsible for the internal human temperature being maintained at 37 degrees Celsius).

Answer 12

The combustion of coal and natural gas releases energy to heat the water, producing steam which drives a turbine. This, in turn, generates electricity using electromagnetic properties. The faster the turbine spins, the more electricity is generated.

Answer 13

Photovoltaic cells convert sunlight into electricity, through the surface materials that allow electrons to absorb photons of light.

Answer 14

A - Steam turbines are cheap with readily available fuels. Can be a renewable energy source if burning biofuels to power the steam turbines. D - Produces CO2 that will contribute to the enhanced greenhouse effect. Can be a non-renewable energy source if burning coal or natural gas.

Answer 15

A - Does not generate greenhouse gases during operation. Are a renewable energy source. D - Carbon emissions are associated with the production of photovoltaic cells. They require sunlight to function. Photovoltaic cells are very prone to breakage due to environmental exposure. They take up large amounts of space.

Answer 16

REDOX reactions are chemical reactions that involve the transfer of electrons from one chemical species to another.

Answer 17

The loss of electrons or an increase in oxidation number is oxidation. The gain of electrons or a decrease in oxidation number is reduction.

Answer 18

An oxidant/oxidising agent is the chemical species that brings on oxidation, but undergoes reduction itself. A reductant/reducing agent is the chemical species that brings on reduction, but undergoes oxidation itself.

Answer 19

1. Separate into half equations. 2. Identify the species being oxidised and reduced using oxidation numbers. 3. Balance the atoms within the equation. 4. Balance any oxygen using water. 5. Balance hydrogen atoms with hydrogen ions (if acidic conditions). 6. Balance electrical charges by adding electrons. 7. Balance electrons by multiplying the entire half equations. 8. Combine both half equations to give the REDOX equation. 9. Cancel species that appear on both sides.

Answer 20

Oxidation occurs at the anode and reduction occurs at the cathode.

Answer 21

Fuel cells are devices that convert chemical energy of a fuel and some oxidant into electrical energy. They are similar to batteries (both galvanic cells) but do not run down or require charging and produce electricity indefinitely, as long as a consistent flow of reagents is supplied.

Answer 22

Hydrogen fuel cells use chemical energy of hydrogen to cleanly produce electricity. The oxidation of hydrogen gas occurs at the anode, which produces electrons that move to the cathode - generating an electrical current. Electrons produced at the anode, flow to the cathode where reduction occurs to convert protons (H+) and oxygen to water. CHECK POWERPOINT FOR DIAGRAM

Answer 23

Energy conversion is from chemical energy to electrical energy, in a spontaneous reaction. Oxidation occurs at the anode. Reduction occurs at the cathode. The electron flow is from anode to cathode. The sign of the anode is negative, and the sign of the cathode is positive. The anion movement from the salt bridge is to the anode, whilst the cations move to the cathode.

Answer 24

Primary cells are non-rechargeable, designed to be used once, is a non-reversible reaction, and once the anode has been consumed no further reaction can occur meaning it can no longer produce electrical current.

Answer 25

Secondary cells are rechargeable, and convert chemical energy into electrical energy by a reversible REDOX reaction. Their reversibility allows cells to be recharged using direct current (DC) electricity. During discharging, the electron flow is from anode (-) to cathode (+). During recharging, the anode and cathode reverse charge meaning the anode is positive and the cathode is negative, but the electron flow is still from anode to cathode.

Answer 26

They have unlimited capacity (electrolytes are stored externally and therefore have wide potential for use), and the cells are rechargeable (electrolytes can be used indefinitely). They can be discharged for extended period and recharged indefinitely without loss of output. They produce no emissions of atmospheric pollutants during operation, and can be laid out in varying configurations (buried and stored within tanks underground).

Answer 27

Flow cells are rechargeable fuel cell that can be used to store power (e.g. wind and solar). They can be charged and discharged via reversible REDOX reactions.

Answer 28

Fuel cells are low cost, high reliability, low maintenance, have a long run time, and produce low pollution. Batteries are low cost and high reliability, but they are high maintenance (require frequent replacing), run down quickly, release pollutants during operation, and have a short life.

Answer 29

Two electrolyte solutions are separated by a proton exchange membrane. This only allows for the flow of electrons and protons, whilst preventing the solutions from mixing.

Answer 30

Hydrogen has the highest energy density per gram and its combustion yields only water: H2 (g) + 1/2O2 (g) --> H2O (l) delta H= -286kJ/mol

Answer 31

Hydrogen energy does not produce carbon dioxide during operation, reducing contributions to the enhanced greenhouse effect. It can also be used as a fuel source for vehicles, further reducing demands for diesel and decreasing emissions from the transport sector. Hydrogen can also act as reductant, reducing iron oxide to iron. This removes the need for coal based iron production, reducing coal demand.

Answer 32

Steam methane reforming (SMR), biomass gasification, and the electrolysis of seawater.

Answer 33

Steam methane reforming is a process that involves heating methane obtained from natural gas (fossil fuel) in the presence of steam and a catalyst: CH4 (g) + H2O (g) <--> CO (g) + 3H2 (g)

Answer 34

A - SMR involves large scale production of hydrogen, and existing infrastructure and systems (as it is used to produce most hydrogen worldwide). D - The reaction produces carbon monoxide as well as hydrogen. It uses a non-renewable natural gas, and requires constant heating supply by fossil fuel combustion.

Answer 35

Biomass gasification is a controlled process that uses heat, steam and oxygen to convert biomass (carbon organic compounds) to hydrogen and carbon monoxide: C (s) + H2O (g) <--> CO (g) + H2 (g)

Answer 36

A - Greenhouse gas emissions are significantly lower as biomass removes carbon dioxide from the atmosphere during growth. D - Produces carbon monoxide.

Answer 37

Science is a global enterprise that relies on clear communication, international conventions, and review and verification of results. International collaboration is often required in scientific investigation.

Answer 38

Development of complex scientific models and/or theories often requires a wide range of evidence from many sources and across disciplines. New technologies improve the efficiency of scientific procedures and data collection and analysis. This can reveal new evidence that may modify or replace models, theories, and processes.

Answer 39

Advances in scientific understanding in one field can influence and be influenced by other areas of science, technology, engineering, and mathematics. The acceptance and use of scientific knowledge can be influenced by social, economic, cultural, and ethical considerations.

Answer 40

Scientific knowledge, understanding, and inquiry can enable scientists to develop solutions, make discoveries, design action for sustainability, evaluate economic, social, cultural, and environmental impacts, offer valid explanations, and make reliable predictions. The use of scientific knowledge may have beneficial or unexpected consequences; this requires monitoring, assessment, and evaluation of risk and provides opportunities for innovation. Science informs public debate and is in turn influenced by public debate; at times, there may be complex, unanticipated variables or insufficient data that may limit possible conclusions.

Answer 41

Seawater has the potential to produce hydrogen gas from an essentially inexhaustible supply. An electrical current is applied at the cathode, resulting in the reduction of water: H2O (l) + 2e- --> H2 (g) + 2OH- (aq)

Answer 42

The electrolysis of seawater requires an energy input that is much higher than the energy output from hydrogen. If that energy is produced through fossil fuels, this process is both environmentally and financially costly. If the energy needed is produced through a renewable source (solar or wind), this process produces green hydrogen and is considered a renewable source.

Answer 43

A -The use of seawater makes hydrogen essentially inexhaustible. If paired with a renewable energy source, the generation can be considered green. D - Hydrogen extraction requires more energy input than released during hydrogen combustion. High energy input is very costly.

Answer 44

Metal reactivity describes how easily a metal undergoes oxidation.

Answer 45

Metals that are higher within the series are more likely to oxidise (from solid metal to ion form), meaning they will displace metals lower in the series (reducing them to solid form).

Answer 46

The reactivity of metal ions is the ease at which a metal ion is reduced. This is the reverse of the reactivity series.

Answer 47

Water is positioned between aluminium and zinc on the metal reactivity series. This means that metals below water will be reduced if in a REDOX reaction with water, as water will be more reactive and oxidise. The elements above cannot be reacted with water if wanting to be obtained in solid form, as water will reduce instead due to its lower position on the reactivity series.

Answer 48

To prevent the formation of iron oxide (rust) on metal surfaces, they are coated with a metal that appears higher on the metal reactivity series. This means the external layer will be oxidised first, preventing the rusting of the underneath metal.

Answer 49

Extraction, concentration, conversion, reduction and refining.

Answer 50

Extraction is the removal of metal ore from the Earth's crust. Ores with high percentages of the metal are mined, and then techniques such as AAS (atomic absorption spectroscopy) are used to identify the concentration of metal within the ore.

Answer 51

The extracted metal ore tends to be crushed and milled into a powder to increase the surface area to volume ratio. The powder then undergoes froth floatation to separate the mineral from the gangue.

Answer 52

The powdered ore and gangue mixed with water to form a slurry. Frothing agents and collectors are added. Air is blown through the slurry and it is stirred to create bubbles. The non-polar region of the mineral attaches to the air bubble, which rise to the surface of the slurry and carry the mineral with it. The froth is skimmed off and the excess water is removed. Waste gangue sinks to the bottom.

Answer 53

Depending on the context of the question, the metal must be converted into a soluble form (for metals below water in the reactivity series) or into molten form (for metals above water in the reactivity series). This prepares them for reduction via electrolysis or chemical reduction.

Answer 54

For example, zinc sulfide (ZnS) is converted into zinc oxide (ZnO) via roasting with air (heating in furnace). The zinc oxide is then leached (extracted from a solid by dissolving) with sulfuric acid (H2SO4) to produce zinc sulfate (ZnSO4). The zinc sulfate solution is then filtered to remove any suspended solids. Zinc powder is then added to precipitate any less reactive metal ions.

Answer 55

Carbon is alongside water, between aluminium and zinc. Hydrogen is between lead and copper.

Answer 56

The anode is positive, the cathode is negative, but the electron flow is still from anode to cathode. It is a non-spontaneous reaction and requires an external voltage source.

Answer 57

The soluble metal compounds are dissolved in water and either undergo chemical reduction using carbon/carbon monoxide or are implemented into an electrolytic cell, to undergo aqueous electrolysis. Whilst the molten metal compounds undergo the electrolysis of molten solutions, as they cannot be in REDOX reaction with water because the water will reduce (due to its lower position on the reactivity series). This reduces the metal to solid form, often of high purity.

Answer 58

Molten electrolysis requires a vast amount of energy to be undertaken, meaning it is an extremely expensive process.

Answer 59

Biofuels are produced by present day biological processes, over shorter time periods than fossil fuels. They can be replenished quicker than they are used, meaning they are a renewable source.

Answer 60

A furnace charged with carbon generates carbon monoxide to be used as a reducing agent: 2C (s) + O2 (g) --> 2CO (g) The metal compound is then combined with the carbon monoxide and undergoes reduction, to form solid metal and carbon dioxide.

Answer 61

Chemical reduction uses blast furnaces that are help at temperatures of 1000 degrees Celsius. These high temperatures are created and maintained by fossil fuels, producing large amounts of carbon dioxide. Electrolytic reduction does not require high temperatures, and is energy and cost saving when compared with chemical reduction or molten electrolysis.

Answer 62

Recycling metals is becoming increasingly important to conserve finite resources.

Answer 63

The recycling of metals: - conserves finite resources (both metals and fossil fuels are used in metal production) - reduces energy requirement (lower energy cost to recycle than produce from ores) - reduces mining (mining is damaging to the environment, it creates waste materials and is expensive) - reduces landfill (sulfur oxides/acid rain, nitrogen oxides/photochemical smog, soot, carbon monoxide and greenhouse gases are all generated in metal production - reduces waste materials (waste is harmful to the environment) - reduces landfill (recycling reduces the amount of waste products sent to landfill)

Answer 64

Physical recycling of polymers involves breaking them down by shredding or melting. Chemical recycling of polymers involves breaking them down to be reused to make new polymers or used as fuel.

Answer 65

Recycling polymers: - conserves fossil fuels (most polymers are created from petroleum, a finite fossil fuel feedstock) - minimises energy requirement (lower energy cost to recycle than synthesise from scratch) - reduces landfill (recycling reduces the amount of waste products sent to landfill)

Answer 66

Thermoplastics and thermosets.

Answer 67

Thermoplastics: - contain dispersion forces or hydrogen bonding between the polymer chains - soften when heated, harden and become more rigid when cooled - can be recycled by heating and reshaping - can be recycled many times until the polymer chains decompose

Answer 68

Composite materials are formed by combining two or more materials with diverse properties. They combine to form unique properties as they do not dissolve or blend into each other.

Answer 69

Thermosets: - contain a high degree of cross-linking (covalent bonds) - do not soften or change shape when heated (will char or burn if heated sufficiently as the covalent bonds break and the polymer decomposes) - cannot be recycled, except for shredding into smaller pieces to become a filler material

Answer 70

ADVANTAGES: - improved properties (advantages of both materials can be utilised, to form a material with improved properties than the original materials) - designed for specific use (since properties can be altered, composite materials are extremely versatile and can be tailored for specific use) DISADVANTAGES: - harder to recycle (the mixing and incorporation of different components prevents them from being separated by heat)

Answer 71

The raw source inclusing: - locational impurities - intended use (i.e. level of purification)

Answer 72

Water that is safe to drink is referred to as potable water. Freshwater is treated to remove suspended solids and is disinfected. Saltwater is treated via desalination processes.

Answer 73

Metals that are lower on the metal reactivity series are less likely to oxidise. This means, when exposed to the natural environment, they will likely remain in reduced (solid metal) form. Whereas, metals that are higher on the metal reactivity series are more likely to undergo oxidation, meaning they will naturally be found in ion form (combined with other substances).

Answer 74

1. Coagulation - chemical process of neutralising the surface charge of particles. 2. Flocculation - physical process of clustering (aggregation) of impurity particles. 3. Sedimentation - setting of the floc aggregates. 4. Filtration - removal of solid impurities. 5. Disinfection - removal of any biological contaminants. 6. Fluoridation - controlled adjustment of fluoride content within water.

Answer 75

Due to the presence and weathering of rocks, suspended inorganic solids are found within water, specifically clays (materials composed of aluminium, silicon and oxygen). Clay particles are extremely small, within the micrometer range, meaning they filter through regular filtration methods. Therefore, they must be bonded and made more dense to be removed.

Answer 76

A true solution is where a substance is homogenously dispersed within another substance, and has a particle size in the nanometer or smaller range. A colloidial solution has particles within the nanometer and micrometer range, which is where clay particles are classified. Anything with greater particle size than micrometer is considered a suspension, and are able to be removed by using gravity.

Answer 77

Any two particles of the same charge will repel. During coagulation, chemicals are added to neutralise surface charge. For clay, salts of highly charged cations and/or charged polymers are added and attract the negatively charged clay particles. This causes the suspension to become destablised and dispersions forces allows the particles to aggregate, joining them together in layers to create microflocs. These microflocs, which are not soluble in water, eventually settle at the bottom as a sediment and can be removed.

Answer 78

The amount of salt present within seawater is much higher than what can be processed by the human body. As saltwater is a true solution, the salt cannot be removed in the same method as freshwater. Desalination methods must be applied additionally.

Answer 79

Reverse osmosis and thermal distillation.

Answer 80

Reverse osmosis is a filtration technique whereby water is forced, under pressure, through a semi-permeable membrane. Pressure is applied to the side with higher salt concentration, which overcomes the osmotic pressure. The water then passes through the semi-permeable membrane but the solute (salt) remains trapped on the other side.

Answer 81

Saltwater is heated until boiling, when the water becomes steam. The pure water vapour is then condensed by coolant to collect the pure water.

Answer 82

Microorganisms, specifically waterborne infectious bacteria, could all still be present within the water.

Answer 83

Plants require nutrients for growth and to carry out normal cellular processes such as photosynthesis, respiration and reproduction. Plants take up these nutrients as water soluble ions present in the soil solution via their root system.

Answer 84

There is a finite amount of nutrients present in dirt. Growing plants depletes the nutrients meaning it is vital to replenish them for plant production.

Answer 85

NPK: - nitrogen (required for the synthesis of amino acids, proteins, enzymes, DNA, RNA and chlorophyll) - phosphorus (required for the synthesis of DNA, RNA, phospholipids and ATP) - potassium (regulates water transport and opening/closing of stoma) These elements must be present in ion form that is soluble in water, as plants take up water from the soil.

Answer 86

Natural nitrogen fixation, synthetic nitrogen fixation, decay of nitrogen containing organisms, and bacterial nitrification.

Answer 87

Nitrogen fixation is repairing the nitrogen content within the soil. Nitrogen, N2, is extremely inert and relatively stable due to the presence of a strong triple covalent bond. Therefore, extremely high energy must be applied to separate the molecule into ions.

Answer 88

Lightning, volcanic activity and forest fires are the only natural forces which are able to provide sufficient energy to break the strong N2 covalent triple bond. This allows it to then react with atmospheric oxygen to form nitrogen oxides: N2 (g) + O2 (g) --> 2NO (g) (nitric oxide) 2NO (g) + O2 (g) --> 2NO2 (g) (nitrogen dioxide) Nitrogen dioxide then dissolves in water vapour in the atmosphere forming nitrous acid (HNO2) and nitric acid (HNO3): 2NO2 (g) + H2O (l) --> HNO2 (aq) + HNO3 (aq) Both acids ionise, producing soluble nitrate ions (NO3-) and nitrite ions (NO2-) which are deposited in the soil during rain fall: HNO3 (aq) + H2O (l) --> H3O+ (aq) + NO3- (aq) (full ionisation - strong acid) HNO2 (aq) + H2O (l) <--> H3O+ (aq) + NO2- (aq) (partial ionisation - weak acid)

Answer 89

Nitrogen-fixing bacteria contain the nitrogenase enzyme that can convert atmospheric nitrogen into fixed forms of nitrogen such as NH3 (ammonia) and NH4+ (ammonium ions): N2 (g) --> NH3 (g)/NH4+ (aq) Nitrifying bacteria in the soil further oxidise ammonia and ammonium ions into nitrite ions (NO2-) and nitrate (NO3-): NH3 (g)/NH4+ (aq) --> NO2- (aq) --> NO3- (aq)

Answer 90

The synthetic Haber process converts atmospheric nitrogen (N2) to ammonia (NH3) under high temperature and pressure: N2 (g) + 3H2 (g) --> 2NH3 (g) This ammonia can then be used in fertilisers to replenish the nitrogen content in soil.

Answer 91

Nitrogen containing compounds can also enter the soil through the waste from living animals and plants. When decreased animals and plants start to decay, aerobic and anaerobic decay takes place: AEROBIC: N containing compound + O2 (g) --> NO3- (nitrate ion) ANAEROBIC: N containing compound --> NH3 (ammonia) The nitrate ions can be directly absorbed into plants when dissolved into water from rain.

Answer 92

Denitrifying bacteria in the soil reduce nitrate ions (NO3-) to nitrogen gas under anaerobic conditions: NO3- (aq) --> N2 (g)

Answer 93

In a natural ecosystem, the rate at which plants uptake nutrients from the soil should be balanced by the rate at which nutrients are returned to the soil via the process of decay. As human life is dependent on crop farming to produce food and fuel, the nutrients from the soil are quickly depleted and not replaced as the plants are harvested (no decay). Therefore, the soil becomes infertile and requires fertilisers to grow more crops. Fertilisers improve plant fertility by adding nutrients containing nitrogen, phosphorus and potassium (and other trace elements) into the soil.

Answer 94

Natural fertilisers are broken down by decomposers (bacteria) in soil. This includes manure, compost, blood and bone, and wood ash. Artificial fertilisers consist of nutrients within a water-soluble compounds and can be taken up by plants directly from fertilisers. This includes ammonium nitrate/sulfate, urea, calcium dihydrogen phosphate, and potassium chloride.

Answer 95

After periods of heavy rainfall, excess nitrogen and phosphorus from fertilisers or sewage can be leached from soils into waterways. The increase in available nutrients promotes the excessive growth of aquatic plants including photosynthetic microbes, specifically algae and bacteria. These microbes form a bloom which prevents sunlight from reaching into the waterway, meaning aquatic plants are unable to photosynthesise. This causes them to die and decompose, both aerobically and anaerobically, to deplete the oxygen supply in the water and generate toxic products. This makes the environment less habitable and causes the death of aquatic organisms.

Answer 96

Eutrophication.

Answer 97

Carbon feedstock is a finite resource. If it is mostly being used for energy generation in fossil fuels, less will be available for plastic/medicinal production and more carbon dioxide will be emitted into the atmosphere - worsening the enhanced greenhouse effect. However if it is mostly being used for plastic/medicinal production, less will be available for energy generation. This means more recycling will be required to avoid increased waste pollution, and greenhouse gas emission will increase due to the production processes.

Answer 98

Aqueous glucose is anaerobically fermented using microorganisms to form bioethanol and carbon dioxide.

Answer 99

A - renewable feedstock for bioethanol, and consumes carbon dioxide during growth. D - more food crops will require more fertiliser, and prevents food security as food crops are required for fuel.

Answer 100

A - production and operation using biodiesel produces less greenhouse gases than using diesel, and reduces diesel demands which conserves finite resources. D - biodiesel has a lower energy density than diesel meaning trucks will cover less distance before refueling.

Answer 101

Flow cells store an amount of energy that is proportional to their electrolyte volumes. Tank size can be scaled up or down based on the battery's required input and output, which is not possible for other galvanic cells.

Answer 102

Flow cells have very large storage capacity. This means they can store the massive quantities of energy produced by photovoltaic cells and wind turbines.

Answer 103

hydrogen + oxygen --> water delta H= -286 kJ/mol NO CARBON DIOXIDE EMISSIONS

Answer 104

Hydrogen is an incredibly flammable gas, so its storage is an issue. We currently lack the infrastructure to support the manufacture and distribution of hydrogen based electricity.