topic 8; fuels

• describe the 3 forms of cracking

  • thermal cracking; 750 degrees, high pressure (70 atm), 
  • catalytic cracking; 500 degrees, low pressure, 
  • vapour passed over zeolite powder(catalyst);
  • contains aluminium oxide + silicon oxide
  • steam cracking; vapour mixed with steams and heated to high temp
• define cracking

  • larger saturated hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules (alkanes AND alkenes)
  • thermal decomposition reaction
• what are the fractions of crude oil

  1. LPG (liquid petroleum gas - propane, butane)
  2. petrol
  3. kerosene
  4. diesel
  5. heating oil (heavy fuel oil)
  6. hot liquid bitumen
• describe fractional distillation

  1. crude oil is heated and vaporised 
  2. then fed into the bottom of the fractional column which is cooler at the top
  3. the vapour rises and condenses into separate fractions depending on their boiling points 
  4. small hydrocarbon molecules have weak intermolecular forces so low boiling points thus do not condense but leave the column as a gas (LPG)
  5. long hydrocarbon molecules (strong IMF) leave the column as hot liquid bitumen
• describe combustion reactions

  • if enough O2 is available = complete combustion (releases loads of energy)
  • [hydocarbon + oxygen -> carbon dioxide + water] HC. gets oxidised
  • exothermic reaction
• what is crude oil an important source of

  • fuel e.g. petrol, diesel
  • feedstock for the petrochemical industry
  • solvents, lubricants, detergents
• describe crude oil

  • complex mixture of hydrocarbons
  • finite resource in the earth's crust
  • -> from the remains of organisms that lived + died millions of years ago
  • (mainly plankton, which was buried in mud)
• what happens in incomplete combustion?

  • the fuels used are not burnt properly
  • limited supply of air, incomplete combustion may produce carbon monoxide and soot
• how do u test for the products given off when a hydrocarbon is burnt?

  • water - blue cobalt chloride turns pink in contact with water
  • limewater - turns cloudy when carbon dioxide is present
• steam cracking

  • heat long chain of hydrocarbon so it turns into gas
  • mix with steam
  • heat to high temperature 
  • hydrocarbon spits into a shorter alkane + alkene 
• what is catalytic cracking?

  • heat long chain of hydrocarbon so it turns into gas
  • use hot powdered aluminium oxide as the catalyst 
  • pass gas over catalyst 
  • as gas touches catalyst it turns into a shorter alkane + alkene
• describe why carbon monoxide is harmful to humans

  • when we breathe it in, it diffuses in our bloodstream and binds to our haemoglobin
  • the reduces the amount of oxygen haemoglobin can carry
  • this means less oxygen is transported to the tissues
• incomplete combustion can lead to soot, what are the effects of this?

  • causes respiratory problems as the particles damage our lungs
  • forms clouds of smog which reflect light back to space
• What is acid rain?

  • rain that’s been made acidic by certain pollutants in the air
  • (sulphur dioxide or nitrogen dioxide)
• What are solutions for acidic rain?

  • burn fuels that don‘t contain sulphur
  • reduce the need to burn sulphur fuels
  • car share, public transport, walk, cycle 
  • neutralise acid lakes and soils with alkalis
• How is temperature related to greenhouse gases?

  • greenhouse gases in the atmosphere maintain temperatures high enough to support life 
  • thermal radiation gets reradiated in all directions, including earth, which warms the atmosphere 
• What are scientists predicting about climate change?

  • human activities will cause the temperature of the earth’s atmosphere to increase at the surface
  • global climate change.
• What are the features of sulphur dioxide?

  • colourless, pungent smelling gas
  • air pollutant responsible for acid rain
  • causes damage to aquatic organisms, pollutes crops/water and irritates lungs/throat/eyes
  • causes corrosion to structures made of carbonate rocks
• What are the features of oxides of nitrogen?

  • produces photochemical smog.
  • causes breathing difficulties.
  • contributes to acid rain.
• what was the early atmosphere of the Earth like?

  • first billion years the atmosphere was very dry with lots of volcanic activity
  • high amounts of CO2, water vapour and nitrogen
  • small amounts of methane and ammonia
  • like the atmosphere of mars and venus today
• how did oceans form?

  • water vapour condensed to form liquid oceans
  • most CO2 dissolves in the oceans to form weak acids
  • weak acids reacted with minerals in the sea to form precipitates
  • over time, this formed sediments of carbonate rock on the sea bed
• how have green plants changed the atmosphere?

  • around 2.7 billion years ago, photosynthetic algae evolved in the oceans
  • photosynthesis produces oxygen which entered the atmosphere
  • over billions of years, plants evolved which increases the amount of oxygen in the atmosphere
  • at some point, there was enough oxygen in the air for animals to evolve
  • photosynthesis also takes in CO2 
  • the carbon can be trapped in fossil fuels which causes the levels to fall
• how is coal formed?

  • from the remains of ferns and trees
  • if they die in marshy wetlands, they don't decompose due to lack of oxygen or acidic conditions
  • these factors prevent bacteria from carrying out decomposition
  • plant remains are covered with sediment and compressed
  • high temperature and pressure create coal
• what are some uses of alcohols?

  • used as fuels as they release lots of energy or as solvents in the industry as they dissolve things water can’t
  • hydrocarbons and lipid compounds 
• how is oil formed?

  • crude oil is formed from plankton
  • when they die, they settle on mud in the sea bed
  • if oxygen isn't present then they don't decompose
  • they are compressed by sediment
  • heat and pressure convert them into crude oil
• how is natural gas formed?

  • it's mainly methane
  • found near deposits of oil
  • formed from plankton like oil
• explain the greenhouse effect

  • solar radiation from the sun passes through the atmosphere and hits the earth
  • some of this energy is reflected straight back toward space, and some of it is absorbed by the earth and then re-emitted toward space
  • some of the energy makes it all the way to space, but much of it is absorbed by small molecules called greenhouse gases
  • these molecules then re-emit the energy and the whole process of absorption and emission happens over and over again
  • this trapped energy keeps the atmosphere warmer and more stable
• name one effect of global warming

  • one effect of global warming is the melting of ice caps
  • this will increase the volume of water in the ocean and could lead to seasonal flooding, or the submersion of entire islands
  • this is made worse by the fact that water expands when it is heated, so it will also increase in volume
• give three general ways we could reduce the carbon footprint of a product

  • create it using fewer or more sustainable raw materials
  • use a more efficient manufacturing process
  • use renewable energy sources
• why is it hard to use more renewable energy resources, rather than fossil fuels?

  • renewable energy resources are more expensive
  • many of our existing products (e.g. cars) require fossil fuels