P2C22 - Hydrocarbons Flashcards
What is the homologous series?
A series of compounds with the same general formula.
What are the properties of hydrocarbons?
Long chain HC = Higher boiling point
Long chain HC = Higher viscosity
Longer chain HC - Less flammable
What is cracking?
The process that breaks down long-chain hydrocarbons into shorter-chain molecules that are more useful.
What is cracking an example of?
Thermal decomposition reaction
What are the 2 ways of cracking?
Catalytic cracking
Steam cracking
What is catalytic cracking?
Vaporised heavy hydrocarbons are passed over the top of a heated catalyst.
Alkanes and alkenes are produced by this reaction.
What is steam cracking?
Vaporised heavy hydrocarbons are mixed with steam in a high temp environment.
The products include alkanes and alkenes.
What are the properties of homologous series?
- Similar chemical properties
- Changeable physical properties
- Neighbouring compounds differ by CH2 unit.
- Same general formula
What does high viscosity mean?
Its thicker, so flows less easily.
What does the combustion of hydrocarbons need?
Good oxygen supply
What does combustion involve?
Energy release.
The oxidation of carbon and hydrogen to create carbon dioxide and water.
What can be created if alkanes aren’t burnt with enough oxygen? (Incomplete combustion)
Carbon monoxide
2C + O2 = 2CO
What is the properties of carbon monoxide?
Colourless
Odourless
Toxic
Binds to haemoglobin in blood
What are the problems with incomplete combustion?
As well as producing carbon monoxide, incomplete combustion produces soot.
Soot can build up in appliances and cause problems. This happens in cars and any items that use carbon compounds as fuel.
What does incomplete combustion create?
Soot
Carbon monoxide
What is sulfur?
An impurity found in fossil fuels
What happens to sulfur when burned?
Sulfur oxidises when burned. This produces the toxic gas sulfur dioxide.
What happens if sulfur dioxide reacts with water?
It forms sulfuric acid which is a major component in acid rain.
What can acid rain do?
Acid rain causes steel corrosion, the weathering of buildings and statues, and the death of insects, plants, and aquatic organisms.
What can cause nitrogen and oxygen to react?
Hydrocarbons being burned in a confined space (High temps can cause them to react)
What can hydrogen fuel cells replace?
They can be used as alternatives to petrol as fuel in cars,
What are the advantages of hydrogen fuel cells?
- The only waste product is water since they use hydrogen and oxygen.
- They produce more energy per gram of hydrogen relative to petrol.
What are the disadvantages of hydrogen fuel cells?
Hydrogen is stored at high pressure and hydrogen gas is explosive.
Not many places to refuel either.
What are hydrocarbons?
Molecules of just hydrogen and carbon
Whats the general formula for alkanes?
Cn H2n + 2
Why are alkanes saturated?
Their bonds are single
What are the alkanes?
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
Pentane (C5H12)
What features of alkanes make them useful fuels?
Quite unreactive
Burn well
What is an alkene?
hydrocarbons with the functional group C=C.
What are the features of an alkene?
Reactive
What is the general formula for alkenes?
CnH2n
Why are alkenes unsaturated?
Double bonds.
WHat are the 4 alkenes?
Ethene C2H4
Propene C3H6
Butene C4H8
Pentene C5H10
What are functional groups?
A collection of atoms that impact the reactions of an organic compound.
What happens when an alkene reacted with bromine water?
This causes the solution to change colour from orange-brown to colourless.
E.g. ethene (C2H4) (colourless) + bromine (Br2) (orange-brown solution) → dibromoethane (CH2BrCH2Br) (colourless).
What happens when alkenes react with steam?
Alcohols can be formed.
Ethene (C2H4) + steam (H2O) → ethanol (C2H5OH)
How can an alkene react with hydrogen?
ONLY IF a nickel catalyst is present, an alkane can be formed.
E.g. Ethene (C2H4) + hydrogen (H2) → ethane (C2H6)
What is hydrogenation?
Adding hydrogen atoms across a carbon-carbon double bond
What happens when an alkene reacts with oxygen, but their combustion reaction is incomplete?
They burn with a smokey flame.
What happens during an alkene addition reaction?
A carbon-carbon double bond opens up
What is an addition reaction?
When a double bond opens up allowing new atoms to bond.
