Flashcards in Fuels and Earth Science Deck (37):
What is crude oil?
Our main source of hydrocarbons
What is crude oil used for?
Used as a feedstock (raw material) to create lots of useful substances used in the petrochemical industry (basically to make different types of petrol)
How is crude oil formed?
Formed underground over millions of years from the buried remains of plants and animals
What is a hydrocarbon?
a compound that contains carbon and hydrogen - in crude oil they are arranged in chains or rings and are usually alkanes (have a general formula of Cn H2n+2)
What are alkanes?
Hydrocarbons with the formula CnH2n+2
What are fractions? (in relation to crude oil)
fractions are simpler, more useful mixtures containing groups of hydrocarbons of similar lengths (similar no. of hydrogen and carbon atoms) - fractions from crude oil include petrol, kerosene and diesel
How are fractions in crude oil separated?
using fractional distillation - oil is heated until most of it has turned into a gas - gases enter a fractionating column (and the liquid bit - bitumen - is drained off at the bottom) - in the column there is a temperature gradient (cooler at top) so the longer hydrocarbons with higher boiling points turn back to liquids and drain out of the column early on and shorter hydrocarbons drain out later on - near to the top of the column (there are different heights where different length hydrocarbons (fractions) drain)
Which different heights on a fractionating column do different crude oil fractions drain out?
1. bitumen - 70+ carbon atoms in each hydrocarbon in this fraction (stays liquid when heated and drained out bottom)
2. fuel oil ~40 carbon atoms in each hydrocarbon
3. diesel oil ~20 carbons
4. kerosene ~15 carbons
5. petrol ~8 carbons
1. gases ~3 carbons (go out the top of the fractionating column)
What are the different fractions in crude oil used for?
1. bitumen - surfacing roads and roofs
2. fuel oil - fuel for large ships and power stations
3. diesel oil - fuel in some cars and larger vehicles e.g. trains
4. petrol - fuel in cars
5. gases - domestic heating and cooking
do you understand fractional distillation of crude oil (pg 137)
What is a homologous series?
a homologous series is a family of molecules with the same general formula and similar chemical properties e.g. alkanes and alkenes are differing homologous series of hydrocarbons - neighbouring compounds in a homologous series differ by a CH2 unit (e.g. Methane: CH4 and Ethane: C2H6)
What does the size of a hydrocarbon determine?
- intermolecular forces of attraction are stronger in bigger hydrocarbons = higher boiling point (so determines which fraction of crude oil it will separate into)
- shorter hydrocarbons = easy to ignite bc lower boiling points mean they're gases at room temp so they mix with oxygen easily which make them flammable (where as longer hydrocarbons are liquid at room temp)
- longer hydrocarbons = higher viscosity bc stronger force between hydrocarbon molecules so harder it is for the liquid to flow - thicker so higher viscosity (how well it flows)
What does viscosity mean?
How hard it is for a substance to flow - longer hydrocarbons are thicker so have a higher viscosity
Why do hydrocarbons make good fuels?
very exothermic - combustion reactions that happen when you burn them in oxygen give out lots of energy
What is a complete combustion?
When hydrocarbons are burned in enough oxygen so that the only products are carbon dioxide and water
What is incomplete combustion?
When hydrocarbons burn in a limited supply of oxygen
What does incomplete combustion produce?
carbon monoxide and soot - e.g. in boilers which use carbon compounds as fuel (and when there isn't enough oxygen for a complete combustion - which would produce water and CO2)
What are the dangers of incomplete combustion reactions?
- produce carbon monoxide (CO) that combines with red blood cells and stops blood from carrying oxygen around the body - lack of oxygen to brain causes fainting, comas and death
- tiny carbon particles are released into the atmosphere, falling back to the ground as soot which makes buildings look dirty, reduces air quality and worsens respiratory problems
What harmful gases do fossil fuels release when burned?
- CO2 (causing global warming)
- Sulfur Dioxide (from sulfur impurities in fuels - forms sulfuric acid in clouds - acid rain which makes lakes acidic and trees die, killing wildlife, damages limestone buildings/statues and corrodes metal)
- Nitrogen Oxides (when nitrogen reacts with oxygen in air - caused by energy released in combustion reactions - cause acid rain and photochemical smog, causing breathing difficulties, tiredness and headaches)
What can be used as a clean, renewable fuel to power vehicles?
What are the advantages of using hydrogen gas to power vehicles?
- very clean (combines with oxygen in a fuel cell to produce energy, water is the only waste product, no greenhouse gases)
- obtained from water which is a renewable resource (waste product is water so this can in theory be used again)
What are the disadvantages of using hydrogen gas to power vehicles?
- special, expensive engine required
- hydrogen gas must be manufactured which is expensive and uses energy from another source which probably uses fossil fuels
- hydrogen is hard to store and not widely available
What is cracking?
turning alkAne (long) hydrocarbons into smaller, more useful alkAne molecules +alkEne molecules which are used to make polymers (e.g. plastics)
How is cracking a form of thermal decomposition?
one substance breaks down into at least two when being heated - covalent bonds need to be broken so a lot of heat energy is needed (catalysts are often added to speed the process)
Why are longer hydrocarbons cracked?
longer molecules are cracked into smaller molecules as there is a higher demand for products like petrol than products like bitumen, so more molecules are needed
What catalyst is used in cracking?
Explain the process of cracking.
1. alkane is heated until it is vaporised
2. vaporised hydrocarbons pass over a powdered catalyst (aluminium oxide)
2. the long-chain molecules split apart or "crack" on the surface of the catalyst - producing short-chain alkanes and alkenes
How does cracking help to match supply and demand?
if one fraction is in high demand, the hydrocarbons from another fraction can be cracked to supply it
How do scientists think our atmosphere may have evolved? (really long but kinda easy but also important sorry)
1. Volcanoes gave out steam and CO2 (Earth's surface was originally molten, eventually it cooled, forming a thin crust, but volcanoes kept erupting, releasing gases from inside, this degassing released mostly CO2, so things settled down and the early atmosphere was now mostly CO2 and water vapour which condensed to form oceans)
2. Green plants evolved and produced oxygen (a lot of CO2 also dissolved into oceans, Nitrogen gas arrived in the atmosphere after ammonia and oxygen reacted and it was released by denitrifying bacteria, this kept increasing as it was unreactive so couldn't be broken down, green plants evolved over the earth and photosynthesised, taking CO2 and making O2, oxygen levels increased and carbon dioxide decreased as it was locked up in sedimentary rocks and fossil fuels)
3. Ozone Layer allows evolution of animals (build-up of oxygen killed off early organisms but allowed the evolution of more complex organisms that used oxygen, oxygen also created the ozone layer that blocked harmful solar rays and enabled even more organisms to evolve, virtually no CO2 is left now)
How do you text for oxygen?
test for oxygen by checking if the gas will relight a glowing splint
How does human activity affect the composition of the air?
- growing population means more respiration so more CO2
- larger population means more energy is needed for lighting, cooking, heating etc and countries becoming richer and industrialised so average energy demand per person increases - increased energy consumption means more fossil fuels are burned so more CO2 is released
- people take up more land so deforestation occurs - meaning less plants to take away CO2
- CO2 also produced by volcanic eruption
Explain the process of the greenhouse effect.
1. sun gives out EM radiation
2. most EM radiation passes through the atmosphere
3. some EM radiation (with short wavelengths) is absorbed by the Earth - warming our planet
4. the Earth radiates some of this heat radiation as infrared (which has a longer wavelength than the energy taken in)
5. some of this infrared radiation is re-emitted back into space, some is absorbed by greenhouse gases, and some is reflected back to Earth by these greenhouse gases - warming the planet
6. enhanced greenhouse effect occurs when more heat radiation is absorbed than sent back to space
What are greenhouse gases?
gases in the atmosphere, present in small amounts, that absorb and reflect heat radiation
How is methane gas causing climate change?
methane is an extremely effective greenhouse gas - concentration of methane has risen rapidly due to human activity e.g. farming as it is produced in the digestive processes of livestock e.g. cattle
What does it mean if global warming is anthropogenic?
that it is caused by humans
Why is historical global warming data less accurate than current records?
because data was taken over fewer locations and the methods used were less accurate - however analysis of fossils, tree rings and gas bubbles in ice can estimate CO2 levels but these are less precise and only include certain locations