C12 - Alkanes

Question 1

What is the general formula pf alkanes?

Answer 1

CnH2n+2

Question 1

What are alkanes mainly used for?

Answer 1

Fuels

Question 2

What type of covalent bond is present in alkanes?

Answer 2

Sigma bond

Question 3

What is a sigma bond?

Answer 3

Head on overlap of two orbitals, one from each bonding atom
Two electrons shared

Question 4

What is a covalent bond

Answer 4

Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 5

Where is the bond positioned in a sigma bond?

Answer 5

Line directly between the two bonded carbon atoms

Question 6

How many sigma bonds does a carbon atom have?

Answer 6

4
either C-C/C-H

Question 7

What is the shape and bond angle of alkanes?

Answer 7

Tetrahedral
109.5

Question 8

How is crude oil seperated?

Answer 8

Fractional distillation

Question 9

What is fractional distillation?

Answer 9

Separation of components in a liquid mixture by their different boiling points into fractions with different compositions

Question 10

Effect of chain length on boiling point

Answer 10

-Inc chain length
-Greater surface area of contact
-Stronger London forces
-Req more energy to overcome

Question 11

Effect of branching on boiling point

Answer 11

-More branching
-Less surface area of contact
-Weaker London forces
-Req less energy to overcome

Question 12

Are alkanes reactive?

Answer 12

Not really

Question 13

Why aren’t alkanes reactive?

Answer 13

-Sigma bonds in C-C and C-H are strong
- C-C bonds are non-polar
- C-H bonds considered non-polar due to similar electronegativity value

Question 14

Equation for complete combustion of alkanes?

Answer 14

CnH2n+2 + O2 –> CO2 + H2O

Question 15

Equation for incomplete combustion of alkanes?

Answer 15

CnH2n+2 + O2 –> CO + H2O

Question 16

What is the molar gas volume formula?

Answer 16

volume = molar gas volume (24dm^3) x amount
V = Vm x n

Question 17

What are the conditions and products of the reaction of alkanes with halogens

Answer 17

alkane + halogen –> haloalkane + hydrogen halide
UV radiation

Question 18

What is the mechanism for the halogenation of alkanes?

Answer 18

Free radical substitution

Question 19

What are the three stages of radical substitution?

Answer 19

Initiation
Propagation
Termination

Question 20

What happens during initiation?

Answer 20

Covalent bond broken by homolytic fission
Under UV radiation
Forms to halide radicals

Question 21

What happens during propogation?

Answer 21

Chain reaction involving two steps
1) Halide radical reacts with C-H bond, forming a new radical and a hydrogen halide
2) New radical reacts with halogen molecule to form the new organic product and a halide radical
(can continue until all the reactants are used up)

Question 22

What is a chain reaction?

Answer 22

Reaction in which the propagation step releases new radicals that continue the reaction

Question 23

What happens during termination?

Answer 23

All radicals combine in pairs forming 3 compounds

Question 24

What are limitations of radical substitution?

Answer 24

-Further substitution
-Substitution at different points on the carbon chain