Alkanes

Question 1

[ALKANES] Why do we need to recycle

Answer 1

Petroleum finite resource
reduced amount of waste
conservation of natural resources

Question 2

[ALKANES] saturation

Answer 2

saturated

Question 3

[ALKANES] hybridisation

Answer 3

sp3 hybridised, tetrahedral, bond angle 109.5

Question 4

[ALKANES] general formula for alkanes

Answer 4

C_nH_2n+2

Question 5

[ALKANES] general formula for cycloalkanes

Answer 5

C_nH_2n

Question 6

[ALKANES] mp bp trend down homologous series

Answer 6

increasing bp and mp down sereies

Question 7

[ALKANES] BP

Answer 7

low bp
weaker idid interactions

1. greater no of e, greater polarisation of e cloud, stronger idid, more energy needed
   
   1. straight chain more surface area, extensive idid, more energy needed

Question 8

[ALKANES] solubility

Answer 8

Soluble in non polar, insoluble in water and polar

Question 9

[ALKANES] density

Answer 9

less dense than water
increases with the size of molecule from
higher MR and idid

Question 10

[ALKANES] chemical reactivity

Answer 10

generally unreactive
strong colvalen bonds, hard to break
single bond, no area of high e density to attract eectrophile
C-C C-H are non polar bonds
No e deficient C to attract nucleophiles

Question 11

[ALKANES] possible reactions

Answer 11

Combustion
FRS

Question 12

[ALKANES] combustion EXO OR ENDO

Answer 12

highly exo

Question 13

[ALKANES] combustion state

Answer 13

must be gaseous

Question 14

[ALKANES] combustion types

Answer 14

complete and incomplete

Question 15

[ALKANES] complete combustion condition and eqn

Answer 15

excess oxygen/more normal air than fuel
C_nH_2n+2 + 3n+1 /2 O₂ → nCO₂ + 2H₂O

Question 16

[ALKANES] incomplete combustion condition and eqn

Answer 16

limited oxygen
Soot - C as product
no soot - CO as product

Question 17

[ALKANES] FRS Overall eqn

Answer 17

Question 18

[ALKANES] FRS 3 mechanisms

Answer 18

1. Initiation 2. Propagation 3. Termination

Question 19

[ALKANES] FRS long story

Answer 19

Question 20

[ALKANES] FRS presentation of half arrows

Answer 20

Only half arrows for initiation but not propagation or termination

Question 21

[ALKANES] reaction with halogens

Answer 21

Reactivity decrease down group
F: explosive
Cl and Br: FRS only in UV light, no reaction without UV
Cl>Br
I: no reaction

Question 22

[ALKANES] Enthalpy of of FRS down the group of halogens

Answer 22

Since H= BB-BF
= (C–H) - (H–X)
More endo down the group
Halogen atom size increase, orbital more diffuse, overlap of H and X less effective, hence more endo

Question 23

[ALKANES] predicting ratio of mono sub products of FRS

Answer 23

1. number and type of H atoms
2. stability of alkyl radicals formed

Question 24

[ALKANES] order of stability of alkyl radicals and REASONS

Answer 24

Tert > secondary > primary > methyl radical
alkyl groups are e donating, increase e desity in e deficient C, stabilising it
hence increased substitution→greater stability, more products WEE

Question 25

[ALKANES] harmful compounds that can be converted

Answer 25

Hydrocarbons [O] to CO2 and H2O
CO [O] to CO2
NO_x converted to N2