Alkanes Flashcards
1
Q
Describe Alkanes
A
- their general formula is CnH2n+2
- They are the main components of natural gas and crude oil
- They are used as fuels
2
Q
What is the shape of alkanes?
A
- a tetrahedral with the bond angle of 109.5 degrees
3
Q
What causes the tetrahedral shape of alkanes?
A
- each carbon atom is surrounded by 4 pairs of electrons which cause 4 sigma bonds
- This causes repulsion between these electron pairs resulting in the tetrahedral shape
4
Q
What factor increases the boiling point
of alkanes
A
- Chain length
5
Q
What factor decreases the boiling point of alkanes
A
- branching
6
Q
Why does increased chain length increase boiling points
A
- The longer the chain length, the larger the surface area of contact
- This increases the strength of london forces so more energy is required to overcome the bonds in the alkane
7
Q
Why does branching decrease boiling points
A
- The more branching, the less the surface area of contact in alkanes decreasing london forces
- Also, by increasing branching, the molecules are further apart than in straight chains decreasing intermolecular forces
8
Q
Why do alkanes have low reactivity? (3 reasons)
A
- Carbon to carbon bonds are very strong (high bond enthalpy)
- Carbon to carbon bonds are non polar
- the electronegativity of carbon and hydrogen is so similar that carbon to hydrogen bonds are considered non polar
9
Q
Why do alkanes non polarity make them in reactive?
A
- It makes it difficult for alkanes to attract other molecules and ions
10
Q
What are the conditions for combustion of alkanes
A
- plentiful oxygen
11
Q
What is the equation for the complete combustion of alkanes
A
Alkanes + oxygen = carbon dioxide and water
12
Q
What type of reaction is combustion
A
- an exothermic reaction
13
Q
what is the balancing order for equations
A
- carbon
- hydrogen
- oxygen
14
Q
What are the conditions of incomplete combustion
A
- limited oxygen supply
15
Q
What are the products of combustion
A
- carbon monoxide and water
- carbon and water
16
Q
what are the issues with carbon monoxide
A
- it can cause health issues such as lung problems
- it is a toxic gas
