Fuel & Earth Science Flashcards
Homologous Series characteristics
Gradual change in physical properties
Similar chemical properties
Formula differs by CH2
Why are hydrocarbons good fuels
When burned they release a lot of energy
Alkane formula
Cn H2n+2
Carbon single bond with four hydrogen bonds, saturated
Alkene formula
Cn H2n
carbon double bond and 2 hydrogen bonds, unsaturated
Crude oil is
- a complex mixture of hydrocarbons- molecules of carbon chains with hydrogen
- split into smaller, more useful, important fractions, ranging between short & long length chain
- finite resource
Properties of small chain hydrocarbons compared to long chain
- shorter has a lower BP as intermolecular forces are weaker in shorter
- short hydrocarbons are easy to ignite due to their low BP, long are hard to ignite
- shorter molecules are less viscous
Process of fractional Distillation for crude oil
- oil is heated until most is turned to gas
- the gas is put into a fractionating column apart from bitumen (liquid is drained off)
- temperature gradient in the column (hot at bottom, cooler at top) means the longer hydrocarbons with higher BP turn to liquid and drain out, into different sections, first. Shorter chain drain off later on at the top of the column
Names and uses of fractions
Gas- cooking, heating Petrol- car fuel Kerosene- plants fuel Diesel- train and truck fuel Fuel oil- large ship fuel and power stations Bitumen- used to roof houses and
Products of complete and incomplete combustion
Complete = oxygen + hydrocarbon —> carbon dioxide + water
Incomplete = limited oxygen + hydrocarbon —> carbon monoxide (also some soot) and water
carbon monoxide can be fatal due to lack of oxygen in brain
soot reduces air quality
How is carbon monoxide a toxic gas
Prevents red blood cells from carrying oxygen around the body
- odourless
- colourless
- stays near the ground so can suffocate people in their sleep
How does acid rain occur
And its effect
Impurities in fossil fuels releases some sulphur and nitrogen
Reacts with oxygen to form sulphur dioxide and nitrogen oxide
Pollutes water, killing fish and possibly animals
Damages leaves of trees- so can’t photosynthesise
Causes metal corrosion
Hydrogen fuel advantages and disadvantages
Pros- only product is water, abundant resource, renewable as taken from water
Cons- hard to transport (must be pressurised) which is expensive, hydrogen leaks can cause explosions, hydrogen stations would have to be implemented, manufactured using energy
Explain what Cracking is
Cracking is the breakdown of longer chain saturated hydrocarbons (alkanes), into smaller chain, more useful and unsaturated molecules (alkenes)
Process of cracking
Hydrocarbons are heated until vaporised, pressured and added to a catalyst
Why use cracking
Demand for shorter chain molecules is greater as they ignite easier and so are better fuels
