Combustion

Incomplete vs complete combustion

	Complete combustion	Incomplete combustion
What is it?	When fuels react with oxygen to release useful energy.	When fuels react with a poor supply to release useful energy.
Word equation	Hydrocarbon + Oxygen ⇒ Carbon Dioxide + water	Hydrocarbon + Oxygen ⇒ Carbon Monoxide + carbon + water
Why is it a problem?	They release carbon dioxide which is bad for the environment.	They release carbon monoxide which is poisonous. The soot is also bad for our lungs.
Flame colour	Blue	Yellow
Bunsen air hole open or closed?	Open	Closed

 

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	prefix
1	Meth-
2	Eth-
3	Prop-
4	But-
5	Pent-
6	Hex-

 

Types of Hydrocarbons

 

Class	Distinguishing feature	General formula	Structure	Name structure	Example
Alkane	Every Carbon atom is bonded to at least two hydrogen atoms	CnH2n+2		Prefix + ane	Ethane
Alkene	Has a double bond	CnH2n		Prefix + ene	Ethene
Alcohol	Has an O-H	CnH2n+1O		Prefix +anol	Ethanol
Carboxylic Acid	Has a double bonded oxygen and an O-H	CnH2nO2		Prefix + anoic acid	Ethanoic acid
Ester	Formed by combining an alcohol and a carboxylic acid. So has two carbon chains. Also has -C-O-C-	CnH2nO2		Prefix (alcohol) +yl + Prefix(cooh) + anoate	Ethyl Ethanoate

 

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

1. Crude oil ( a mixture of hydrocarbons) enters the furnace and is heated to around 350°C.
2. The heated mixture enters the fractionating column
3. All but one hydrocarbon boils at this temperature, so they rise up the fractionating column, leaving behind bitumen. ( A material used to make roads)
4. As the mixture of hydrocarbons cools, one by one the boiling points of the hydrocarbons are reached and they begin condensing.
5. When The hydrocarbons condense they are separated form the mixture and the liquid is siphoned off.
6. The mixture of gases continues to rise until only the hydrocarbons which are gases at room temperature are left.
7. 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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