Alkanes Flashcards
Definition of hydrocarbon
A compound with hydrogen and carbon atoms only
Definition of saturated
A compound with single carbon atoms only
Definition of fraction
A mixture of compounds with similar size molecules and similar boiling points
Why do different alkanes have different boiling points?
- Chain length.= increase number of molecules means more electrons means greater induced dipole dipole forces of attraction.
- Branching.= more branching means less surface contact between molecules so decreased into dipole dipole forces of attraction.
Steps of fractional distillation
- Crude oil is heated to vaporise it and enter the column.
- Hydrocarbons have different boiling points depending on MR./chain length/size
- Column is cooler at the top and hotter at the bottom
- Larger molecules with larger boiling points condense at the bottom.
Purpose of cracking
To make alkenes and shorter chain molecules which are more useful and more in demand
What are the two types of cracking?
Thermal
Catalytic
Thermal cracking
High temperature=700-1200k
High pressure =7000kpa
Produces one alkane and other molecules being ours
Catalytic cracking
High temperature=700k
Slight pressure =100kpa
Produces branched alkanes and cycloalkanes
Uses a zeolite catalyst
Complete combustion
Using oxygen
Producing carbon dioxide and water
Incomplete combustion
Produces C which is a solid/ CO (g) and H2O
How is sulphur dioxide formed?
Most crude oil contain sulphur as a impurity which when is burned produces sulphur dioxide
S(s) + O2(g) → SO2(g)
Acidic rain by sulphuric acid equation
SO2(g) + 0.5 O2(g) + H2O(l) → H2SO4(l)
This causes various problems, including erosion of buildings and statues, killing of plants and
trees, and killing of fish through contamination of lakes.
How is NO/ NO2 formed?
High temperatures in car engines
N2(g) + O2(g) → 2NO(g)
2NO(g) + O2(g) → 2NO2(g)
Acidic rain by nitric acid
4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(g)
What is flu gas desulfurisation ?
Processes of removing flu gases such as sulphur which are released through power station chimneys by neutralising with an alkali
What are the two methods of desulfurisation ?
- Calcium oxide and water sprayed onto flu gas to make calcium sulphate.
- Passing the flu gas through calcium carbonate.
Calcium oxide and water to make calcium sulphate
CaO(s) + 2H2O(l) + SO2(g) + 0.5 O2 → CaSO4.2H2O(s)
Passing flue gas through calcium carbonate
CaCO3(s) + 0.5 O2(g) + SO2(g) → CaSO4(s) + CO2(g)
Benefit of catalytic converters
They have a honeycomb structure made of platinum and rhodium metals which increase the rate of reaction. They convert more harmful gases into less harmful gases
Removal of carbon monoxide and nitrogen monoxide
2NO(g) + 2CO(g) → N2(g) + 2CO2(g)
Removal of unburnt hydrogen carbons and nitrogen monoxide
C8H18 + 25NO → 8CO2 + 9H2O + 12.5N2
What are single carbon bonds composed of?
Sigma bond only
What are double carbon bonds composed of?
Sigma and pi bond
Why is there no rotation around a double carbon bond?
The π bond is formed by overlap of p orbitals
• If there was any rotation, the p orbitals would no longer overlap and the π
bond would break
What is an electrophile
Electron pair acceptor
What is a nucleophile ?
Electron pair donor
