Topic 4 - Managing Resources Flashcards
How are fossil fuels formed? + Examples
Fossil fuels are formed over geological time scales by anaerobic decomposition of dead organisms under metamorphic conditions. Examples include coal petroleum and natural gas.
What classifies non-renewable energy?
Non-renewable energy is when the reserves are depleted quicker than they can be formed.
State and explain the two main uses of carbon-based fuels.
The two main uses of carbon-based fuels are providing energy from combustion and feedstock for the chemical industry. Energy generation from combustion is the result of releasing energy stored within bonds. Feedstock is the chemical manufacture of products using carbon-based fuels as the raw materials.
What classifies renewable energy? + Examples
Renewable energy is generated from natural resources over time scales of years to decades, that are replenished quicker than they can be used. Examples include sunlight, wind, biodiesel, geothermal and hydroelectric.
What is bioethanol and how is it used?
Ethanol (C2H5OH) can be considered an alternative fuel source to petrol, reducing diesel demands. It can be blended with petrol to form E10 fuels (10% ethanol) or just used pure.
How is bioethanol produced?
Bioethanol is produced anaerobically and exothermically through the fermentation of simple carbohydrates (e.g. glucose) by microorganisms (e.g. yeast).
What is the formula for bioethanol production directly from plant sources that contain simple carbohydrates?
C6H12O6 (aq) –> 2C2H5OH (l) + 2CO2 (g) delta H= -ve kJ/mol
What is the formula for bioethanol production indirectly from the hydrolysis of complex carbohydrates?
(C6H10O5)n (aq) + nH2O (aq) –> nC6H12O6 (aq)
How is fractional distillation used in bioethanol production?
Fractional distillation (separation based on boiling points) can be used to separate ethanol from the reaction mixture, increasing the concentration and purity of the bioethanol obtained.
What is biodiesel and how is it produced?
Biodiesel is an alternative to petroleum diesel and can be easily incorporated into diesel blends. It is derived from triglyceride sources from animal fats, oils, plants and algae.
What is the general worded equation for transesterification? + Write the equation for bio-methanol production and check with powerpoint.
triglyceride (esters in triglyceride) + alcohol -catalyst-> propane-1,2,3-triol (glycerol) + mixed alcohol esters (biofuel)
SEE POWERPOINT
What is combustion?
Combustion is a reaction between a fuel and an oxidant (oxygen) that occurs at high temperatures.
What is required for complete combustion to occur? What are the reactants and products of complete combustion?
Complete combustion occurs when there is a sufficient supply of oxygen to convert all carbon atoms into carbon dioxide.
fuel + oxygen –> carbon dioxide + water delta H= -ve kJ/mol
What are the conditions and products of incomplete combustion?
Incomplete combustion is due to a low supply of oxygen, resulting in the partial oxidation of carbon in the fuel (to form carbon monoxide and soot).
Where does incomplete combustion commonly occur?
Incomplete combustion commonly occurs during the combustion of fuels in industrial furnaces and combustion engines.
What is the correlation between chain length and incomplete combustion?
As the length of carbon chains in the fuel increases, the ratio of carbon to oxygen increases - limiting the availability of oxygen to form carbon dioxide. Larger molecules also have stronger dispersion forces making them less volatile fuel sources (more energy required to disrupt interactions), reducing the ability to mix effectively with gaseous oxygen during combustion.
What happens to degree of saturation as chain length increases?
Hydrocarbons with longer chains have an increased degree of saturation, as the number of hydrogens increase.
What are the effects of carbon monoxide? Use an equation to support your explanation.
Carbon monoxide binds to haemoglobin (the molecule used to transport oxygen within blood) more strongly than oxygen, shifting equilibrium to decrease oxygen transport aroung the body.
Hb(O2)4 + 4CO (g) <–> Hb(O2)4 + 4O2 (g)
Low concentrations of CO can cause fatigue and dizziness, whilst high concentrations can cause loss of consciousness and death.
What are the effects of carbon soot?
Soot can limit visibility in urban areas by blackening surfaces, causing visual pollution. It also covers leaves of plants, reducing photosynthesis and stunting growth. Due to the black colour, it can absorb solar radiation and cause localised warming, decreasing reflectivity and further contributing to global warming.
What are thermochemical equations and what comprises them?
Thermochemical equations represent the chemical change and associated energy change for a chemical reaction. The equations must be fully balanced (molar enthalpy for one mole of fuel) with fractional values to balance oxygen, have states for all species, and enthalpy value shown (delta H).
What is enthalpy?
Enthalpy (H) is the total energy/heat of the system at constant pressure and volume.
What is enthalpy change?
Enthalpy change is the difference in the potential energy of the reactants and the products for a chemical reaction.
What does enthalpy change do in exothermic and endothermic reactions?
If enthalpy change is positive (products higher than reactants), it is exothermic (heat absorbed).
If enthalpy change is negative (reactants higher than products), it is endothermic (heat released).
What is calorimetry?
The measurement of heat energy change during a chemical reaction, or change of state.
How is bomb calorimetry set up?
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.
What are the common errors in bomb calorimetry?
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.
What is enthalpy of combustion?
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.
What is the formula for quantity of heat released in combustion?
Q=m x c x delta T (joules)
What is molar enthalpy of combustion and the formula?
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)
What is the specific heat capacity of water?
c=4.18 (J/g/degrees Celsius)
What is the formula for specific energy (heat released per gram)?
specific energy = delta H/MW (kJ/g)
What is the energy density formula (heat released per litre)?
energy density = (delta H/MW) x p (kJ/L)
where p is density
What is the comparison of fuel abilities used for?
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.
Describe photosynthesis with the chemical and worded equations. Is it exothermic or endothermic?
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).
Describe respiration with the chemical and worded equations. Is it exothermic or endothermic?
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).
How does traditional energy generation (steam turbines) work?
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.
What are photovoltaic cells?
Photovoltaic cells convert sunlight into electricity, through the surface materials that allow electrons to absorb photons of light.
What are the advantages and disadvantages of steam turbines?
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.
What are the advantages and disadvantages of photovoltaic cells?
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.
What is a REDOX reaction?
REDOX reactions are chemical reactions that involve the transfer of electrons from one chemical species to another.
Definition of oxidation and reduction.
The loss of electrons or an increase in oxidation number is oxidation. The gain of electrons or a decrease in oxidation number is reduction.
Definition of oxidant and reductant.
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.
How are REDOX equations balanced?
- Separate into half equations.
- Identify the species being oxidised and reduced using oxidation numbers.
- Balance the atoms within the equation.
- Balance any oxygen using water.
- Balance hydrogen atoms with hydrogen ions (if acidic conditions).
- Balance electrical charges by adding electrons.
- Balance electrons by multiplying the entire half equations.
- Combine both half equations to give the REDOX equation.
- Cancel species that appear on both sides.
What does anOILRIGcat mean?
Oxidation occurs at the anode and reduction occurs at the cathode.
What are fuel cells and how are they different to batteries?
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.
What are hydrogen fuel cells and how do they work? Draw a diagram of a hydrogen fuel cell and check it against the powerpoint.
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
What are the properties of galvanic cells?
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.
What are the properties of primary battery cells?
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.
What are the properties of secondary battery cells?
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.
What are the advantages of flow cells?
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).
What are flow cells?
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.
