Combustion
Incomplete vs complete combustion
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Complete combustion
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Incomplete combustion
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What is it?
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When fuels react with oxygen to release useful energy.
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When fuels react with a poor supply to release useful energy.
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Word equation
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Hydrocarbon + Oxygen ⇒ Carbon Dioxide + water
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Hydrocarbon + Oxygen ⇒ Carbon Monoxide + carbon + water
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Why is it a problem?
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They release carbon dioxide which is bad for the environment.
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They release carbon monoxide which is poisonous. The soot is also bad for our lungs.
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Flame colour
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Blue
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Yellow
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Bunsen air hole open or closed?
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Open
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Closed
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Energy transferred
This is the amount of energy released minus the amount of energy absorbed.
Fuel efficiency
This is the amount of energy units transferred per mass unit in a fuel.
The most common fuel efficiency unit is Kj/mol
To calculate it do: Energy in kilojoules / Mass in moles
Hydrocarbons
Prefixes
# carbon atoms
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prefix
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1
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Meth-
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2
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Eth-
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3
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Prop-
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4
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But-
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5
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Pent-
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6
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Hex-
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Types of Hydrocarbons
Class
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Distinguishing
feature
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General formula
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Structure
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Name structure
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Example
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Alkane
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Every Carbon atom is bonded to at least two hydrogen atoms
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CnH2n+2
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Prefix + ane
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Ethane
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Alkene
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Has a double bond
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CnH2n
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Prefix + ene
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Ethene
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Alcohol
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Has an O-H
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CnH2n+1O
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Prefix +anol
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Ethanol
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Carboxylic Acid
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Has a double bonded oxygen and an O-H
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CnH2nO2
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Prefix + anoic acid
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Ethanoic acid
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Ester
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Formed by combining an alcohol and a carboxylic acid. So has two carbon chains. Also has -C-O-C-
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CnH2nO2
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Prefix (alcohol) +yl + Prefix(cooh) + anoate
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Ethyl Ethanoate
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Test for alkenes
To test for an alkene, add a few drops of bromine.
Positive:
- Solution changes from orange to colourless.
- The ethene reacts with bromine as ethene is unsaturated (Has a double bond), causing the double bond to break and two bromines to connect. As it is just one molecule, it loses its colour
Negative:
- Solution stays orange
- Bromine can’t bond with a non-ethene as it will be saturated (Does not have a double bond)
Fractional distillation
Boiling points vs Hydrocarbon length
- As the boiling point increases the hydrocarbon length does so as well
- As the length of the hydrocarbon increase the surface area of the hydrocarbon also increases. With a higher surface area there are more Van der Waals forces between molecules. These forces have to be overcome to break apart the molecules to change their state.
How fractional distillation works
- Crude oil ( a mixture of hydrocarbons) enters the furnace and is heated to around 350°C.
- The heated mixture enters the fractionating column
- All but one hydrocarbon boils at this temperature, so they rise up the fractionating column, leaving behind bitumen. ( A material used to make roads)
- As the mixture of hydrocarbons cools, one by one the boiling points of the hydrocarbons are reached and they begin condensing.
- When The hydrocarbons condense they are separated form the mixture and the liquid is siphoned off.
- The mixture of gases continues to rise until only the hydrocarbons which are gases at room temperature are left.
- The gases left are natural gases.
Biofuel
Advantages:
- They are theoretically carbon neutral as it absorbs carbon from the air.
- They are renewable
- Are an alternative fuel, so if other fuels run out we can use it.
- Does not produce soot or ash in the process of combustion
Disadvantages:
- Deforestation is needed to make space for biofuel crops.
- Biofuel crops can only be grown in areas with optimal conditions such as lots of sunlight, rain and heat.
- Biofuels are not really carbon neutral as when you take in account transport, growing and harvesting more carbon the process emits more carbon than is taken in.
- Biofuel takes the place of crops so it could lead to food shortages.
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