Energy Option Flashcards
energy from the sun
comes from uncontrolled nuclear fusion reactions
photosynthesis
- reaction of carbon dioxide and water to form carbohydrates in the presence of chlorophyll
- endothermic
give details of photosynthesis
- green pigment chlorophyll contains an extended system of alternating single and multiple bonds (conjugation)
- substances like chlorophyll contain extended conjugation and are able to absorb visible light by exciting an electron within this conjugated system
- energy which is absorbed by chlorophyll when it interacts with light is able to drive photosynthesis
how can the energy stored in biomass by released?
- direct combustion of plant material
- biogas: anaerobic decay of organic matter by bacteria produces a mixture of methane and carbon dioxide
- fermentation to produce ethanol: carbohydrates can be fermented by enzymes in yeast
biofuel advantages
- renewable
- readily available
- relatively non-polluting
- reduces amount of waste in landfill sites
biofuel disadvantages
- widely dispersed
- take up land where crops can be grown
- remove nutrients from soil
vegetable oils
- derived from glycerol and unsaturated fatty acids
- contain considerable amount of energy
- cannot be used in internal combustion because they are too viscous (because they have a high molar mass)
transesterification
- vegetable oils converted into usable fuel
- ester can react with an alcohol to be converted into a different ester in the presence of strong acid or base
greenhouse effect
warming of the Earth caused by infrared radiation emitted by the Earth’s surface which is absorbed by various gases in the Earth’s atmosphere and then partly re-radiated towards the surface
greenhouse gases
- water vapor
- carbon dioxide
- methane
- nitrous oxide
Why do greenhouse gases absorb infrared radiation?
- resonance
- must be a change in dipole moment as bonds in the molecule stretch and bend
enhanced greenhouse effect
greenhouse effect caused by human activities
energy flow diagram of greenhouse effect
what are two consequences of global warming?
- changes in agriculture and biodistribution as climate changes
- rising sea-levels due to thermal expansion and melting polar ice caps and glaciers
what influences the contribution a greenhouse gas makes to global warming?
- concentration in atmosphere
- ability to absorb infrared radiation
ways to limit human-made emissions of carbon dioxide
- reducing dependency on fossil fuels
- capturing gas chemically using sodium hydroxide or calcium oxide
- stored in certain types of silicon-based rocks
why are coral reefs being destroyed?
- increase in concentration carbon dioxide in atmosphere leads to increase concentration of carbon dioxide dissolved in ocean
- ocean more acidic
particulate
- e.g. soot and volcanic dust
- cool the earth by scattering the shortwave radiation from the sun and reflecting it back into space
energy
ability to do work
first law of thermodynamics
energy within a closed system can neither be created nor destroyed
order for the main energy sources in terms of producing energy
crude oil > coal > natural gas > hydroelectric > nuclear fission > wind > biofuels > solar > geothermal
why is the production of energy not 100% efficient?
heat loss
- to surroundings
- by power lines
energy density equation
energy released from fuel / volume of fuel consumed
specific energy equation
energy released from fuel / mass of fuel consumed
efficiency of an energy transfer
useful output energy / total input energy *100
why must sulfur be removed from crude oil before it is refined?
can poison catalysts by blocking their active sites
fractional distillation
separating crude oil into different boiling fraction
fraction from distillation
- refinery gas: used as fuel on site, gaseous cooking fuel, feedstock for chemicals
- gasoline and naphtha: cars, feedstock for organic chemicals
- kerosene: fuel for jet engines, domestic heating, cracked to provide petrol
- gas oil: diesel engines and industrial heating, cracked to provide petrol
- residue: fuel for large furnaces, vacuum distilled to make lubricants, bitumen used to surface roads
cracking
- process conducted at high temperatures whereby large hydrocarbons are broken down into smaller more useful molecules
- usually alkanes and alkenes
isomerization
more useful branched alkanes can be obtained from straight-chain hydrocarbons by mixing them with hydrogen and heating them at 770K over a platinum catalyst at high pressure
what are other reforming processes?
- cyclization to make ring molecules
- aromatization to make benzene
carbon footprint
- total amount of greenhouse gases produced during human activities
- expressed in equivalent tons of carbon dioxide
where does the majority of the carbon footprint come from?
indirectly from fuel used to produce and transport goods compared with the emissions which come directly from using gasoline in their own car
how can consumers offset their carbon footprint?
- planting trees
- reduce the use of fossil fuels and materials in general
- reuse materials and recycle
knocking
under the conditions of high temperature and pressure the reaction may start before the spark and the engine will be less efficient
octane number
more branched the alkane the higher the octane number
coal gasification
- crushed coal is mixed with superheated steam
- synthesis gas produced: mixture of carbon monoxide and hydrogen
how to produce SNG?
- reacting coal gas with more hydrogen in the presence of a heated catalyst
- heating crushed coal in steam at 700C using potassium hydroxide as a catalyst
SNG
- cleaner gas as it removes pollution due to sulfur dioxide
- easier to transport
- less efficient
Fischer-Tropsch process
- synthesis gas is reacted with more steam to increase the proportional of hydrogen in the mixture
- hydrogen and carbon monoxide are then passed into a fluidized bed reactor containing iron or cobalt catalysts to produce a mixture of hydrocarbons that can be separated by fractional distillation
what is the primary component of natural gas?
methane
coal advatnages
- present in large quantities and distributed throughout the world
- can be converted into synthetic liquid fuels and gases
- feedstock for organic chemicals
- has the potential to yield vast quantities of energy compared with renewable sources
- safer than nuclear power
- longer lifespan compared with oil or gas
coal disadvantages
- contributes to acid rain and global warming
- not so readily transported
- coal waste lead to ground acidity and visual and chemical pollution
- mining is dangerous
- dirty (produces dust, smoke and particulates)
oil advantages
- easily transported in pipelines
- convenient fuel for use in cars
- feedstock for organic chemicals
oil disadvantages
- contributes to acid rain and global warming
- limited lifespan and uneven distribution worldwide
- risk of pollution associated with transportation by tankers
natural gas advantages
- clean fuel
- easily transported in pipelines and pressurised containers
- does not contribute to acid rain
- releases a higher quantity of energy per kg than coal or oil
natural gas disadvantages
- contributes to global warming
- limited lifespan and uneven distribution worldwide
- greater risk of explosions due to leaks
chemical reaction vs. nuclear reaction
- chemical reaction: valence shell electrons rearranged
- nuclear reaction: nucleus itself rearranges
nuclear fusion
small atoms combine to form heavier nuclei
nuclear fission
splitting of heavy nuclei to form two or more lighter nuclei
nuclear safety concerns
- meltdown: occurs when a nuclear reactor becomes out of control and essentially becomes a nuclear bomb
- escape of radioactive material: occur as the fuel is being transported or while it is being used
- high-level nuclear waste: must be stored for a very long time
- low-level nuclear waste: gloves, etc. that have been used in areas where radioactive materials are handled
half-life
time after which the number of radioactive nuclei is reduced by a factor of 2
how can supplies of methane be increased?
- cracking larger hydrocarbons
- coal gasification
