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Stage 2 Chemistry > EXAM REVISION > Flashcards

EXAM REVISION Flashcards

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1
Q

List the disadvantages and advantages of steam turbines.

A

DISADVANTAGES:
- Produces CO2 which is a greenhouse gas molecule.

ADVANTAGES:
- Cheap and there are readily fuels.
- Is a renewable energy source.

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2
Q

Describe what photovoltaic cells are and their advantages and disadvantages?

A
  • They convert sunlight to electricity directly.

ADVANTAGES:
- Doesn’t generate GG in operation
- Is a renewable energy source.

DISADVANTAGES:
- They produce zero pollution, however the process of production of these solar cells results in a lot of carbon emissions which is pollution.

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3
Q

What are fuel cells and their advantages?

A
  • A device that converts chemical energy of a fuel and some oxidant into chemical energy.
  • Similar to batteries (galvanic cells) as they convert chemical energy to electrical energy.

HOWEVER:

ADVANTAGES ARE: They don’t run down or require charging and they will produce electricity consistently as long as the fuel source and oxidant are continuously supplied.

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4
Q

Describe hydrogen fuel cells.

A

-They use the chemical energy of hydrogen to cleanly produce electricity.
- At the anode oxidation is occurring and is oxidizing hydrogen gas which produces electrons that move to the cathode, generating an electrical current.
- At the cathode reduction is occurring and the electrons generated at the anode travel to the cathode where reduction converts O2 molecules to water (H2O).

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5
Q

What are the advantages of fuel cells compared to batteries?

A
  • Both are low in cost, and have high reliability.
    BUT; fuel cells:
  • have low maintenance (they don’t need replacing just a constant supply of the fuel and the oxidant)
  • Low pollution
  • And have a long life (infinite upon constant supply of required elements).
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6
Q

Describe flow cells.

A
  • They are rechargeable fuel cells that can be used to store power (i.e wind and solar).
  • They can undergo charging and discharging due to revisable redox reactions. Charging converts electrical energy to chemical energy and discharging converts chemical energy to electrical energy.
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7
Q

What are the advantages of flow cells over fuel cells?

A
  • They have an unlimited capacity because the electrolytes are stored externally, therefore have wide potential for use.
  • The cells are rechargeable so the electrolyte solutions can be used indefinitely.
  • It can be discharged for extended periods of time and recharged indefinitely without loss of output.
  • No emissions of atmospheric pollutants during operation.
  • Components of the cell can be laid out in varying configurations (ie. tanks can be buried and stored underground).
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8
Q

Why is hydrogen being looked at as a fuel source?

A
  • It has the highest energy density per gram and combustion only yields water by the following reaction:
    H2(g) +1/2O2(g) -> H2O(l) ^H = -268 kJ/mol
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9
Q

What is the issue in using hydrogen as a potential fuel source and what are the advantages?

A
  • Hydrogen is a flammable gas, therefore storage is an issue.
    Currently, we lack the infrastructure to support the manufacture and distribution of hydrogen based electricity.

ADVANTAGES:
- Does not produce carbon dioxide - no GHE
- Can be used a fuel source for vehicles - further reducing emissions of GHG’s from the transport sector.
Hydrogen can also act as a reductant, reducing iron oxide to iron. Removing the need for coal-based iron production, reducing coal demand.

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10
Q

What are the different methods of Hydrogen production?

A
  • Steam methane reforming (SMR)
  • Biomass Gasification
  • Electrolysis of Seawater
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11
Q

Describe steam methane reforming (SMR) in the production of hydrogen and its associated advantages and disadvantages.

A
  • Heats methane obtained from natural gas (from fossil fuels) in the presence of steam and a catalyst.
    Following the reaction equation:
    CH4(g) + H2O(g) <-> CO(g) + HH2(g)

ADVANTAGES:
- Large-scale production
- Existing infrastructure and processes as used for the production of most hydrogen world wide.

DISADVANTAGES:
- Produces carbon monoxide.
- Uses non-renewable natural gas.
- Requires constant heating supplied by fossil fuel combustion.

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12
Q

Describe biomass gasification in the production of hydrogen and its associated advantages and disadvantages.

A
  • A controlled process that uses heat, steam and oxygen to convert biomass to hydrogen and other products.
  • Steam reacts with carbon organic compounds to produce carbon monoxide and hydrogen.
    C(s) +H2O(l) <-> CO(g) H2(g)

ADVANTAGES:
- The GGE are much lower as biomass removes carbon dioxide from the atmosphere during growth.

DISADVANTAGES:
- Produces carbon dioxide.

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13
Q

Describe electrolysis of seawater during hydrogen production and its associated advantages and disadvantages.

A
  • An electrical current is applied at the cathode, which results in the reduction of water by the following equation:
    H2O(l) + 2e- -> H2(g) +2OH-(aq)
  • Requires an energy input much higher than the energy output of hydrogen.

ADVANTAGES:
- An inexhaustible source of the reactant.
- If this energy is produced from a renewable source (solar or wind) this process produces green hydrogen, and is considered a renewable source.

DISADVANTGES:
- Hydrogen extraction requires a higher energy input than energy released during hydrogen combustion.
- High energy input is very costly.
- If this required energy is produced from fossil fuels, this process is both environmentally and financially costly.

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14
Q

What are the steps of metal production?

A
  1. Extraction - removing the metal ore from the Earth’s crust.
  2. Concentration of the mineral.
  3. Conversion of mineral to a compound.
  4. Reduction through either molten electrolysis, aqueous electrolysis and chemical reduction.
  5. Refining
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15
Q

Describe the process of extraction in zinc production.

A
  • Ores containing high percentages of the metal as the mineral are mined.
  • AAS can be used to determine the concentration of the metal within the ore.
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16
Q

Describe the process of concentration in metal production.

A
  1. The extracted ore is crushed and milled into a powder to increase the surface area to volume ratio.
  2. The powder undergoes froth floatation to separate the mineral from the gangue.
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17
Q

Describe the process of froth floatation and what part of metal production is it used in?

A

Used in concentrating the minerals from the metal ore.

  1. The powder is mixed with water to separate the mineral from the gangue.
  2. Frothing agents and collectors are added.
  3. Air is blown through the slurry and it is stirred to create bubbles. The minerals attach to the bubbles and float to the surface.
  4. Froth containing the mineral is skimmed off and excess water is removed.
  5. The waste gangue sinks to the bottom.
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18
Q

Describe the importance of frothing agents and collectors in froth floatation.

A
  • Frothing agents help to create a stable froth (air bubbles) because they are detergent.
  • Collectors are ions that contain a charged anionic region and a non-polar region.
  • The anionic region adsorbs to the surface of the mineral powder the an ionic interaction.
  • And the nonpolar region attaches to the air bubbles which rise to the surface of the slurry and carry the mineral with it.
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19
Q

Describe the process of conversion in metal production.

A
  • Step 3
  • The mineral is converted to an ionic compound so it can be soluble in water to be able to undergo aqueous electrolysis.
  • This conversion is done in two steps. 1 of which is roasting the mineral to form a metal oxide and the next step is leaching it (extracting the metal oxide from a sold by dissolving it) to form an ionic compound.
  • This ionic compound is then filtered to remove any suspended solids and then the metal powder (i.e zinc powder) is added to precipitate any less reactive metal ions.
20
Q

Describe the process of reduction in metal production.

A
  • The ionic compound is dissolved in water to form an aqueous solution.
  • The electrodes don’t interact with the reaction.
  • The positive ions (metal ions) are reduced and are reduced at the cathode and the anions move to the anode where the WATER is oxidized. (2H2O(l) -> O2 + 4H+(aq) + 4e-)
  • If electrolysis is used in metal production, refining is not required because the products are pure.
21
Q

What are the most energy intensive processes of metal production?

A
  • Reduction
  • Roasting
22
Q

What are the advantages of using composite materials?

A
  • They have improved properties compared to their original materials because you can utalise both materials.
  • Are designed for specific uses because their properties can be altered.
23
Q

Explain why it is more difficult to recycle composite materials.

A
  • Because they have mixed components from different materials.
  • A lot of composite materials use thermosets as the matrix, therefore the reinforcements can’t be heated to separate from the matrix.
24
Q

Explain the process of pyrolysis in recycling composite materials.

A

Composite material is heated under oxygen to undergo combustion and burn off the thermoset, and retain the reinforcement fibers.

25
Q

What are the disadvantages of recycling composite materials?

A
  • Limited due to high costs.
  • The resulting separated compounds are low in quality.
  • Have a lack of incentives and infrastructure.
26
Q

How are coagulation and flocculation used to cluster clay?

A

COAGULATION:
- Ionic compounds (salts) are added in coagulation so the strong cations can attract the negatively charged clay particles to neutralize their charge.

FLOCCULATION:
- Suspension becomes destabilized and the dispersion forces between the clay and cations allow the particles to cluster (making larger molecules).
- These are called micro flocs.
- Micro flocs are insoluble in water therefore settle at the bottom.
- The solution is stirred and micro floc combine, increasing mass and particle size so it sinks to the bottom to be later removed as a sediment.

27
Q

What are the advantages and disadvantages of desalination in water treatment?

A

ADVANTAGES:
- produces potable water
- reduces demand of freshwater supplies which is good because sea water is in much large quantities than fresh water.
- Does not depend on the climate, e.g., not effected by drought.
- Thermal distillation and reverse osmosis are becoming more efficient as research continues, e.g., the uses for wasted heat.

DISADANTAGES:
- Both processes require a lot of energy.
- Both processes are expensive due to associated energy input and maintenance.
- Brine is produced as a by-product which requires disposal.
- The generation of heat from these processes can effect local ecosystems.
- Water inlet from the sea has the potential to cause death of aquatic organisms.

28
Q

Explain the process of natural nitrogen fixation with the aid of equations - from natural high energy activities.

A
  1. Lightning, volcanic activity, and forest fires provide sufficient energy to break the triple N2 bond.
  2. N2 reacts with atmospheric oxygen to from nitrogen oxides (same equations as photochemical smog).

N2 + O2 -> 2NO (nitric oxide)
2NO + O2 -> 2NO2 (nitrogen dioxide)

  1. Nitrogen dioxide then dissolves in water vapor in the atmosphere to form nitrous acid and nitric acid.

2NO2 + H2O -> HNO2 + HNO3

  1. Both of these acids can ionize to form soluble nitrate ions (NO3-, NO2-) which can the be deposited into the soil during rainfall.

HNO3 + H2O -> H3O+ + NO3- (full ionization)
HNO2 +H2O <-> H3O+ + NO2- (partial ionization)

29
Q

Explain the process of natural nitrogen fixation with the aid of equations - from nitrogen-fixing bacteria.

A
  1. They contain the nitrogenase enzyme which converts atmospheric nitrogen into fixed nitrogen forms of NH3 and NH4+.

N2 -> NH3/NH4+ (ammonia/ammonium ions)

30
Q

Explain the process of natural nitrogen fixation with the aid of equations - from decay of nitrogen containing organisms.

A
  • Nitrogen containing compounds can enter the soil through waste from living animals and plants.

But also:
- When deceased animals begin to decay, they can break down compounds into soluble nitrate ions.
- Two types:
- Aerobic decay meaning O2 is present:
Nitrogen containing compound -> NO3- (nitrate ion)
- Anaerobic decay meaning absence of O2
Nitrogen containing compound -> NH3 (ammonia)

31
Q

What is nitrification?

A
  • Nitrifying bacteria in the soil oxidize ammonia (NH3) and ammonium ions (NH4+) into nitrate ions (NO2- and NO3-).

NH3/NH4+ -> NO2- -> NO3-

32
Q

What is denitrification?

A
  • Denitrifying bacteria in the soil reduce nitrate ions (NO3-) to nitrogen gas under anaerobic conditions.

NO3- -> N2

33
Q

Explain Synthetic Nitrogen Fixation.

A
  • The synthetic Haber process converts atmospheric nitrogen to ammonia under high pressure and temperature.

N2 + 3H2 -> 2NH3

34
Q

What are advantages and disadvantages of using natural gas as a production method for producing hydrogen?

A

Advantages:
- produces a lot of hydrogen
- natural gas and steam are inexpensive and abundant raw materials
- Natural gas and water are simple to extract and transport.

Disadvantages:
- Natural gas is a fossil fuel, therefore leads to carbon emissions and enhanced GHE.
- Natural gas is non-renewable energy source, therefore production of hydrogen is unsustainable from this source.
- Steam is produced using eat from fossil fuel combustion
- The reaction produces carbon monoxide.

35
Q

What are the advantages and disadvantages of using biomass as a source to produce hydrogen?

A

Advantages:
- Biomass is inexpensive and abundant raw material
- Is a renewable feedstock for hydrogen production
- Minimizes the decomposition of plant waste which releases carbon dioxide

Disadvantages:
- The reaction produces carbon monoxide
- steam is produced using heat from fossil fuel combustion.

36
Q

What are the advantages and disadvantages of using seawater as a source to produce hydrogen?

A

Advantages:
- Seawater is abundant and an inexpensive material.
- can produce hydrogen using electricity from renewable sources.

Disadvantages:
- Requires a lot of energy for electrolysis.
- Maintaining electrolytic cells is expensive.

37
Q

Why is hydrogen a better fuel source than fossil fuels?

A
  • Hydrogen can be produced in a renewable manner.
  • Doesn’t release carbon dioxide when combusted
  • Feedstocks are renewable and abundant
  • Can be locally produced
  • Has high energy efficiency
38
Q

What is an advantage of fuel cells compared to galvanic cells?

A
  • the fuel doesn’t need replacement in a fuel cell whereas electrodes must be replaced in a galvanic cell.
39
Q

Disadvantage of a fuel cell compared to galvanic.

A
  • They require a constant fuel source to keep them running.
40
Q

What are two sources of systematic error that may have resulted in the calculated experimental molar enthalpy value being lower that expected?

A
  1. Heat lost to the environment which results in a bigger difference in temperature, which would create a lower enthalpy value.
  2. Incomplete combustion due to insufficient O2 would cause a decrease in the molar enthalpy value.
41
Q

How do you make a triglyceride. Use the reaction equation.

A

Glycerol + fatty acid (carboxylic acid) —> ester.

Glycerol:
Three carbon going down, with three alcohol groups (propan-1,2,3,-triol).

Carboxylic acid:
3 COOH group’s and a variable R group.

Triglyceride:
Three C-O=O-R

42
Q

Advantages and disadvantages of synthetic polymers.

A

Advantages:
- Polymers replacing glass are cheaper and less dense (lighter).
- Polymers replacing car parts are cheaper, less dense and do not corrode as much.
- Polymers replacing wool and textiles are cheaper and more durable.

Disadvantages:
- Polymers are susceptible to UV damage.
- Polymers are heat sensitive (especially thermoplastics).
- Polymers are non-biodegradable.

43
Q

How do you make photodegradable polymers?

A
  • When synthesizing, include many carbonyl groups because they can be broken down by UV, therefore ensuring that they will degrade overtime by sunlight.
44
Q

What are the advantages and disadvantages of biodegradable polymers?

A

Advantages:
- Reduces the amount of waste in landfill.
- When decomposed, it can be used a a fertilizer for plant crops.

Disadvantages:
- Currently, there are a limited amount of synthetic polymers that are degradable.
- Oxygen and water are required for decomposition and this will not be accessible if they are deep in landfill.
- Greenhouse gasses are released during decomposition.

45
Q

Advantages and disadvantages of biomass derived polymers.

A

Advantages:
- They are derived from a renewable feedstock.
- Plants and crops are a relatively abundant feedstock.
- Plants and crops are easily extracted and processed.
- By-products or waster products from farming crops can be a source of biomass.

Disadvantages:
- This is a new area of research, so currently not that many are being produced.
- The production of synthetically produced biodegradable polymers may compete with land for food production.

46
Q

What are the advantages and disadvantages of petrol derived polymers?

A

Advantages:
- Fossil fuels are an abundant feedstock.
- Petroleum is easily extracted and processed.
- There are existing processes for producing polymers based from petroleum.
- There are a wide variety of polymers produced from petroleum.

Disadvantages:
- Petroleum is a non-renewable feedstock.
- The reserves of petroleum are being used at a much faster rate than they can be replenished - non-renewable.

Stage 2 Chemistry (4 decks)

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