Topic 4: Managing Resources Flashcards
What is the carbon cycle?
The carbon cycle describes the movement of carbon between the atmosphere, oceans, biosphere, and geosphere (carbon reservoirs)
If more carbon enters a carbon reservoir than leaves it, it is referred to as a carbon sink (e.g. oceans)
If more carbon leaves a reservoir than enters it, it is referred to as a net carbon source (e.g. combustion of fossil fuels)
What is photosynthesis?
Photosynthesis is the chemical process by which plants and some microorganisms use carbon dioxide, water, and energy from sunlight to produce oxygen and glucose
6CO2 + 6H2O energy-> C6H12O6 + 6O2
It is endothermic as it requires the absorption of energy from sunlight
What is aerobic respiration?
Aerobic respiration is a series of reactions that occurs in cells that releases energy for metabolic activity
C6H12O6 + 6O2 -> 6CO2 + 6H2O
It is exothermic as it releases energy
What are carbon-based fuels?
Carbon-based fuels include fossil fuels and biofuels
They can undergo combustion with oxygen to release chemical energy used primarily in energy production and transport
They are also used as feedstock (raw material) to produce a range of products
What are fossil fuels?
Fossil fuels have been formed over hundreds of thousands of years through the decay of organic matter under metamorphic (heat and pressure) geological conditions
Includes coal, petrol, and natural gas
Fossil fuels are relatively abundant, very energy dense, and can be easily extracted and distributed (especially thanks to well-established industries)
However, they are a finite and non-renewable source (the rate at which they are consumed exceeds their rate of formation), and their production and use releases many harmful chemicals into that atmosphere that contribute to climate change
What are biofuels?
Biomass fuels are derived from biomass from plants and animal waste matter
Includes bioethanol, biodiesel, and biogas
They provide a renewable alternative to many fossil fuels and are plentiful. They are often described as carbon-neutral as the emissions of carbon dioxide from combustion are offset by the absorption of carbon dioxide by biofuel crops and microbes during photosynthesis
However, they often require larges amounts of land to produce and have little existing infrastructure to produce, transport, and use them
What is renewable energy?
Renewable energy is energy that has been generated from sources that can be naturally replenished such as hydropower, wind power, solar energy, geothermal energy, and biofuels
Direct emissions from the use of renewable sources (apart from biofuels) do not significantly contribute to the production of greenhouse gases
However, the establishment, production, distribution, and ongoing maintenance of technologies related to these sources generate a significant contribution to the release of greenhouse gases, which effects global warming
What is bioethanol?
An alternative fuel source that is often blended with petrol in varying ratios, or is used as a pure liquid in vehicles that have been designed to accommodate the fuel
Bioethanol is produced by yeasts undergoing fermentation (anaerobic respiration), an exothermic process
C6H12O6(aq) enzymes->2C2H5OH(l) + 2CO2(g)
Higher concentrations of ethanol are obtained through fractional distillation
What is biodiesel?
An alternative to petroleum diesel - can be easily incorporated into diesel blends
Derived from triglycerides including fats and oils from plants and algae
Biodiesel is produced through transesterification (displacing one alcohol from an ester with another alcohol) of triglycerides
Methanol (with the aid of a catalyst) reacts with a triglyceride (ester), separating the glycerol and fatty acids by giving its OH to the glycerol and its CH3 to the fatty acid, making it an ester (fatty acid methyl ester)
What does a thermochemical equation represent, and what are its components?
A thermochemical equation represents a chemical change and the associated energy change
Shows the correct balanced species, states of matter, and enthalpy change
When does complete combustion occur?
Complete combustion occurs when there are enough moles of oxygen available to completely oxidise all carbon atoms (in the fuel) into CO2
When does incomplete combustion occur?
Incomplete combustion occurs when there are insufficient moles of oxygen available to completely oxidise all carbon atoms in the fuel, resulting in partial oxidation states, such as C and CO
This is often because it is difficult to maintain the required stoichiometric ratio, so the products include those of both complete and incomplete combustion
Fuels with larger hydrocarbon molecules are more likely to form products of incomplete combustion, as the ratio of carbon to oxygen is larger, limiting the oxygen available to form CO2
Larger molecules also experience stronger dispersion forces, making it more difficult for the fuel to mix with oxygen during combustion
How does carbon monoxide affect humans and animals?
CO can bind to haemoglobin much more strongly than oxygen, shifting the position of equilibrium to favour the formation of carboxyhemoglobin, limiting the amount of oxygen that can be carried around the body (via oxygenated haemoglobin), leading to fatigue and possibly loss of consciousness
How does soot effect the environment and humans?
Soot is comprised of carbon nanoparticles and various products from incomplete combustion
It causes visual pollution in urban areas, blackening surfaces
When soot covers the leaves of plants, it limits photosynthesis and hence plant growth
When landing on snow and ice, it reduces the Earth’s albedo, resulting in more heat being absorbed by the Earth’s surface
When inhaled, it can lead to decreased respiratory function, and may result in the absorption of carcinogens on the surface of carbon
Soot also absorbs solar radiation, causing localised warming on that causes ice to melt and atmospheric temperatures to increase
What is Q in thermochemistry?
Q=mcAT (J) is the quantity of heat released in a combustion reaction, where m is the mass of the heated substance, c is the specific heat capacity of that substance, and AT is the temperature change of the substance
What is AH and what does it represent in thermochemistry?
AH = Q/1000xn (KJ/mol) is the molar enthalpy of a chemical reaction and represents the quantity of heat released or absorbed per mole of fuel that reacts, where n is the moles of fuel reacted
Explain specific energy and energy density
Specific energy (kJ/g) represents the heat released per gram of fuel
Energy density (kJ/L) represents energy released per litre of fuel undergoing combustion
Both are considered when choosing fuels for vehicles, as it is more economical and efficient to generate more energy whilst carrying and burning less fuel
kJ/mol (/Mr)-> kJ/g (x g/L)-> kj/L
How is electricity generated from steam turbines?
Coal and natural gas are combusted to produce high pressure steam, driving turbines linked to a generator, producing electricity
Burning these fossil fuels releases CO2 into the atmosphere, contributing and the heated water can be released to local marine environments, thus affecting surrounding ecosystems
How can electricity be generated from photovoltaic cells?
Photovoltaic cells use semiconductor materials to allow electrons to absorb photons of light and shift them from the semiconductor to generate a current (electricity)
Producing photovoltaic cells produces significant carbon emissions
What are galvanic cells?
Galvanic cells (aka voltaic cells) are electrochemical cells that rely on spontaneous redox reactions to generate a flow of current, converting chemical energy into electrical energy during the reaction when an electrical current is connected
(A battery is a group of cells)
Discuss the two main types of galvanic cells
Typically, the oxidiser and reducer are stored in the cell and are consumed during operation until it is discharged
In a primary cell, one or more reactants become depleted and the cell is disposed of
Secondary (rechargeable) cells can have the redox reactions reversed reforming the reactants, but the generation of reactants is less effective over time
What is a fuel cell?
A fuel cell is a type of galvanic cell where the oxidiser and reducer do not need to be stored or regenerated
Instead, fuels such as hydrogen and methanol are fed directly into the cell, and the oxidant is simply oxygen from the air
Electrode reactions are promoted by a metal catalyst, and a selective membrane separates the half-cells
What is a flow cell?
A flow cell is a rechargeable fuel cell
Two external tanks contain two electrolytes (anolyte and catholyte), which are pumped into the half cells, separated by an ion-selective membrane
As the cell is discharged, they exchange ions through the membrane, generating electricity
When the cells are depleted, electricity is supplied to create an electrolytic cell, moving the ions back to their original states in their respective electrolyte solutions
The electrolyte does not need to be replaced often
Capacity can be increased by simply increasing the size of the tanks
No emissions of atmospheric pollutants during operation
Components can be laid out in varying configurations, including burying the tanks underground
Discuss the advantages and disadvantages of a fuel cell
It uses fuels that are commonly available and renewable (e.g. hydrogen and methanol), which offer high energy density and produce very few, if any, atmospheric pollutants
The components do not need to be replaced if high-quality fuels are used, and are silent during operation
However, hydrogen may be obtained from non-renewable fossil fuels, must be supplied in high purity (electrodes can be easily contaminated), and must be stored safely
The metal catalysts used on the surface of the electrodes are also often expensive and limited in abundance
There is also limited infrastructure surrounding hydrogen transport and refilling
What are the five common stages of metal production?
Extraction – an economically viable body of ore is mined from the Earth’s crust
Concentration – the ore is crushed into powder, and the mineral is concentrated by removing unwanted minerals and waste rock, reducing the costs associated with transportation
Conversion – one or more stages of chemical conversion may be required to convert the mineral to a compound suitable for the reduction stage
Reduction – chemical reduction at high temperatures or electrolysis (molten or aqueous) is used to reduce metal ions to the metal
Refining – further electrolysis or reactions are undertaken to remove remaining impurities, and the metal may also be alloyed at this stage to improve upon properties
Explain electrolytic cells
Electrolytic cells are electrochemical cells that generate non-spontaneous redox reactions by applying an electric current, converting electrical energy to chemical energy
Electrolysis is commonly used to reduce metal ions to metals
The electrodes have opposite charges (compared to galvanic cells), but electrons still flow form the anode to the cathode (and AnOx RedCat is still true)
