Alkanes Flashcards
Order of petroleum fractions
1) Petroleum gas
2) Petrol
3) Naphtha
4) kerosene
5) Diesel
6) Lubricating oil
7) Bitumen
Use of petroleum gas
Fuel for cooking and heating
Uses of petrol
Car fuel
Uses of Naphtha
Raw material for making plastics and detergents
Uses of kerosene
Fuel for aircraft engines
Fuel for cooking and heating
Uses of diesel
Fuel for Diesel engines
Uses of lubricating oil
Lubricants for machines, making waxes and polishes
Uses of bitumen
Paving road surfaces
Name 2 sources of Alkanes
1) crude oil (fractional distillation)
2) natural gas (90% by volume of methane)
Structure of Alkanes
Alkanes are saturated hydrocarbons which contain only single covalent bonds
Structure of Alkenes
Alkenes are unsaturated hydrocarbons which contain double covalent bonds between carbon atoms
What physical properties increase with increase in molecular mass?
1) melting and boiling points
2) density
3) viscosity
What physical property decreases with increase in molecular mass?
Flammability
Why do melting and boiling points increase as molecular size increases?
Attractive forces (van der waals) between Alkane molecules become stronger as molecules become larger
Density of Alkanes
Alkanes are less dense than water, increase as molecular size increases
Viscosity of Alkanes
Becomes more viscous (more resistant to flow) as molecular size increases
Why does flammability (ability to burn) decrease with increase in molecular size?
Alkanes become less flammable and produce a smokies flame as molecular size increases because percentage of carbon in Alkane molecules increases as molecular size increases
*this reason is only accepted if there is a significant difference in percentage
Solubility of Alkanes
Alkanes are insoluble in water (polar reagent) but soluble in organic solvents (eg benzene, ether etc)
Physical properties of branched Alkanes (as branching increases)
1) melting and boiling points decrease
2) density decreases
Why does melting and boiling point decrease as branching increases?
Branching gives the molecules a more spherical shape leading to lower surface area for van der waals interaction and hence reduces van der waals forces between the molecules.
Complete combustion
Forms water and carbon dioxide
Methane + oxygen -> water + carbon dioxide
Incomplete combustion
Methane + oxygen -> H20 + CO
Methane + oxygen -> H20 + C
Reactivity of Alkanes
Generally unreactive because of strong C-C and C-H bonds
What is a substitution reaction?
A reaction in which one or more atoms of an organic compound is replaced by one or more other atoms
Describe halogenation
Alkanes react with halogens in the presence of diffused sunlight (Ultra Violet light). A hydrogen atom in the Alkane is replaced by an atom of the halogen (in a substitution reaction)
Which halogens are fastest in the rate of reaction of Alkanes?
Fluorine > chlorine > bromine
Major product of halogenation
If methane is in excess, major product is chloromethane
If chlorine is in excess, major product is tetra chloromethane
*methane cannot be substituted immediately with4 chlorine atoms to form tetrachloromethane
Describe fractional distillation of crude oil
Crude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures.
(Fractions with lowest boiling points condense at the top and fractions with highest boiling points condense at the bottom)
