Chapter 12 Key Concepts

Question 1

What are Alkanes

Answer 1

• saturated hydrocarbons
• Main component of natural gas and crude oil
• Very stable
• Used as fuel cuz react with O2 to make heat
• Sigma bonds act as axis allowing Alkanes to rotate freely
• tetrahedral 109.5 4CNC with 4BP that repel equally no LP

Question 2

State and explain 2 Factors that affect the boiling point of Alkanes

Answer 2

Lf act between molecules in close surface contact

chain length
-Increases chain length increases SA s= more surface contact possible, stronger Lf, increasing energy required to overcome the forces

branching

• more branching
• less SA of contact
• weaker London forces
• branches also get in the way and prevent branched molecules getting close together like straight chains, further decreasing the intermolecular forces

Question 3

What is fractional distillation and how does it work

Answer 3

Different fractions have different boiling points

Increase the temperature of the system so each fraction vaporises separately from the other fractions and can be collected

Question 4

Why are Alkanes so unreactive

Answer 4

CH and CC sigma bonds are strong

CH electroneg so similar, considered nonpolar

CC bond is nonpolar

Question 5

Why are Alkanes good fuels?

Answer 5

Readily available
Give out heat easy to transport
Burn in plentiful supply without giving out products toxic to humans
*eg methane. Makes up 80% of natural gas. Used in cooking heating and generating electricity
Permafrost contains trapped CO2 and methane in the arctic tundra in Greenland.

Question 6

Drawbacks of radical substitution

Answer 6

Further substitution
-can happen until all the hydrogen atoms have been substituted. So end up with a mixture with varying degrees of substitution

Substitution a different points
-the longer the C chain the more monosub isomers you can get at different positions on the chain