3.2 Alkanes Flashcards
What are alkanes?
Saturated hydrocarbons that only contain carbon-carbon and carbon-hydrogen single bonds
Alkanes are the simplest type of hydrocarbons.
How does the length of the carbon chain affect the boiling point of alkanes?
The longer the carbon chain, the higher the boiling point due to a larger surface area and stronger Van Der Waal’s forces
More electrons contribute to stronger intermolecular forces.
What is the relationship between the branching of the carbon chain and the boiling point of alkanes?
The more branched the carbon chain, the lower the boiling point due to weaker Van Der Waal’s forces
Branched molecules cannot pack as closely together.
What is crude oil?
A mixture of different hydrocarbons
Crude oil is primarily composed of alkanes.
What is petroleum primarily composed of?
Mainly alkane hydrocarbons
Petroleum is separated from crude oil through fractional distillation.
How are deposits of crude oil and natural gas formed?
By the slow decay of marine animals and plants, over millions of years, under heat and pressure, in the absence of air
This process leads to the formation of hydrocarbons.
What affects the exact composition of crude oils?
It varies around the world
Different geographical locations can yield different hydrocarbon compositions.
What is the state of crude oil in its raw form?
Very unreactive and has no use
It must be separated at an oil refinery for practical applications.
What is the first step in the fractional distillation process?
The mixture is vaporised and fed into the fractionating column
This step initiates the separation of hydrocarbons.
What happens to the vapours in the fractional distillation process?
Vapours rise, cool, and condense
This process allows for the collection of different fractions at different temperatures.
What is done with the products after condensation in fractional distillation?
Products are siphoned off for different uses
Each fraction has specific applications based on its boiling point.
What are the boiling point characteristics of products with short carbon chains?
Have lower boiling points and rise higher up the column before reaching their boiling point
These products are collected at the top of the column.
Where are products with long carbon chains collected in a fractionating column?
Collected at the bottom of the column
They have higher boiling points and do not rise far up the column.
What process is used to further break down compounds collected from the fractionating column?
Cracking
Cracking involves the thermal decomposition of alkanes to produce shorter carbon chain products.
What is cracking?
The thermal decomposition of alkanes to produce shorter carbon chain products
It is done to utilize excess fractions with longer carbon chains.
What are the two methods of cracking?
- Thermal Cracking
- Catalytic Cracking
Each method produces slightly different products.
What are the temperature and pressure requirements for thermal cracking?
High temperatures: 400 - 900 °C and high pressure: 7000 kPa
This method produces a high amount of alkanes and alkenes.
What catalyst is required for catalytic cracking?
Zeolite Catalyst
Catalytic cracking requires lower temperatures and normal pressure.
What are the temperature conditions for catalytic cracking?
Requires lower temperatures: 720 K
It operates under normal pressure.
What is the general reaction for cracking?
Long chain alkane → shorter chain alkane + alkenes
Sometimes, more than one product may result from the reaction.
Why are longer carbon chains broken down during cracking?
To form smaller, more useful molecules
Longer carbon chains are not very useful.
What reaction conditions are required to break carbon-carbon bonds during cracking?
Harsh reaction conditions
Necessary to facilitate the cracking process.
What makes alkanes good fuels?
They release lots of energy when burned.
What products are produced during complete combustion of alkanes?
Carbon dioxide and water.
