M4 Chapter 12 - Alkanes Flashcards
What is an alkane?
A saturated hydrocarbon containing C-H bonds only joined together by single covalent bonds.
What is the general formula of alkanes?
CnH2n+2
Are alkane bonds polar?
No because Carbon and Hydrogen have similar electronegativities.
What type of covalent bonds are present?
Sigma Bonds
What is a sigma bond?
The sigma bond is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms.
What is the shape and angle of an alkane?
Tetrahedral (4 bonding regions)
109.5
What do the sigma bonds allow for in alkanes?
They can act as axes around which the atoms can rotate freely. Meaning the shapes are not rigid.
What type of intermolecular force do alkanes have? Why?
London forces because they are non polar.
How to separate crude oil (hundreds of different alkanes) apart?
Fractional Distillation.
What happens to the boiling points as alkane chain length increases? Why?
The boiling point increases as there is more surface area meaning more surface contact between molecules. This make more induced dipole-dipole interactions. Therefore, more energy is required to overcome the forces.
Does a branched molecule have a lower or higher boiling point compared to equivalent straight chain. Why?
The branched molecule has a lower boiling point because they have lower surface contact between molecules meaning fewer London Forces. Therefore, lower amount of heat to break these weaker bonds.
Are alkanes soluble in water? Why?
Insoluble because the hydrogen bonds in water are stronger than alkanes’ London forces of attraction.
How reactive are alkanes? Why?
Very unreactive due to C-C and C-H bonds being strong and the electronegativity of both C and H being so similar that they are considered non-polar.
What reaction will alkanes undergo?
Combustion and reactions with halogens.
What type of reaction is combustion?
Oxidation
What is complete combustion?
Combustion that occurs with a plentiful supply of oxygen to form Carbon Dioxide and Water.
What are the products of complete combustion?
Carbon Dioxide and Water
What is the colour of the bunsen burner during complete combustion?
Blue Flame
What is incomplete combustion and what products are formed in the case of alkanes?
Combustion in a limited supply of oxygen.
Products are Carbon Dioxide, Water, Carbon Monoxide.
Write an equation for the complete combustion of propane.
C3H8 + 5O2 –> 3CO2 + 4H2O
What type of hydrocarbon are most likely to undergo incomplete combustion?
Longer chained hydrocarbons as more moles (amounts) of oxygen are required for the same reaction.
What is the environmental impact of Carbon Monoxide?
Toxic/Poisonous
What is the environmental impact of soot?
Asthma, Cancer, Global Dimming
How are halogenoalkanes formed from alkanes? (Mechanism)
Free Radical Substitution
