12 Alkanes

Question 1

Free Radical Substitution

Answer 1

1. Initiation
2. Propagation
3. Termination
   Reagents and conditions: (limited) X2, UV light

Question 2

General formula for alkanes

Answer 2

C(n)H(2n+2)

Question 3

Cycloalkanes

Answer 3

Saturated cyclic hydrocarbons which form a closed ring structure

Question 4

Melting and boiling points of alkanes

Answer 4

Increases as number of carbon atoms increases
Strength of id-id interactions between molecules increases as number of electrons increases

Question 5

Density of alkanes

Answer 5

Less dense than water
Packing of alkane molecules less efficient than water
Weaker id-id interactions between alkane molecules as compared to stronger hydrogen bonds between water molecules

Increase in density as number of carbon atoms increases (increase in molar mass>increase in volume)

Question 6

Solubility of alkanes in water

Answer 6

Insoluble in water
Water is a polar solvent; alkanes are non-polar -> cannot form effective interactions with water molecules
Energy needed to overcome stronger hydrogen bonds between water molecules > energy released when weaker id-id interactions form between alkanes and water

Question 7

Reactivity of alkanes

Answer 7

Relatively unreactive
Non-polar C-C and C-H bonds -> unreactive towards polar reagents
C-C and C-H bonds very strong

Question 8

Combustion of alkanes

Answer 8

C(x)H(y) + (x+y/4)O2 -> xCO2 +y/2 H2O

Question 9

Stability of hydrocarbon radicals

Answer 9

More substituted radical, more stable the radical
Alkyl substituents are weakly electron-donating, which helps to stabilize the electron deficient carbocation

Question 10

Cracking

Answer 10

Bigger hydrocarbon molecules are broken down into smaller molecules