alkanes Flashcards
What 2 factors affect the boiling points of a homologous series?
- Length of the main chain:
○ Longer ∴ MORE London forces ∴ stronger the
agrac:on ∴ more energy required to overcome. - Surface area of contact:
○ Greater ∴ MORE London forces ∴ stronger the agrac:on ∴ more energy required to overcome.
○ Branching reduces this.
Give 2 reasons why organic compounds are mostly unreacactive
● C-C and C-H have high bond enthalpies.
● Very low bond polarity (essenially nonpolar).
However, they can react with radicals or anything else as reactive as a radical.
What is incomplete combustion, what does this form, and what does this mean in terms of energy?
● Combustion under limited oxygen forming CO and/or C (soot).
● Produces less energy per mole (as less energy is released from
bond making.)
What is cracking?
● Converting long chain hydrocarbons to smaller ones.
● High Mr alkane → small Mr alkane + alkene.
Give 2 problems with synthesising haloalkanes by free radical substitution
● Lots of termination steps lead to impurities (e.g., 2 •CH3 meeting).
● Further substitution of termination products.
Describe the process of fractional distillation
- Heat the crude oil to the highest boiling point.
- Funnel the vapours into a fractionating column which is cooler further up.
- Let the hydrocarbons will rise up and condense and their
respective b.p.’s.
Describe the 3 steps of the synthesis of chloroalkanes (using methane)
- Initiation - UV light is supplies enough energy to break Cl-Cl bonds by homolytic fission.
- Propagation - chlorine radicals remove H atoms from methane to form methyl radicals. These react with Cl2 molecules to form a chloromethane and Cl•. The new radical continues the chain reaction.
- Termination - when all radicals meet other radicals.
what is the general formula of alkanes
CnH2n+2
what are the bond angles in alkane
109.5°
4 bonding pairs
electrons repel as far apart from eachother as possible
