Chapter 12 Alkanes

Question 1

σ-bond

Answer 1

A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with the electron density centred around a line directly between the nuclei of the two atoms.

Question 2

fractional distillation

Answer 2

The separation of components in a liquid mixture by their different boiling points into fractions with different compositions.

Question 3

effect of chain length on boiling point

Answer 3

Increased chain length> greater surface area of contact> stronger London forces

Question 4

effect of branching on boiling point

Answer 4

• more branching
• less surface area of contact
• weaker london forces

Question 5

Reasons for alkanes lack of reactivity

Answer 5

c-c and c-h sigma bonds are strong
c-c bonds are non polar
c-h is non polar

Question 6

complete combustion of an alkane

Answer 6

CxHy + (x+y/4)O2 > xCO2 + y/2 H2O

Question 7

initiation

Answer 7

The first stage in a radical reaction in which radicals starts when a covalent bond is broken by homolytic fission of a covalent bond.

Question 8

propagation

Answer 8

The steps that continue a free radical reaction, in which a radical reacts with a reactant molecule to form a new molecule and another radical, causing a chain reaction.

Question 9

chain reaction

Answer 9

A reaction in which the propagation steps release new radicals that continue the reaction.

Question 10

termination

Answer 10

The step at the end of a radical substitution when two radicals combine to form a molecule.

Question 11

bromination of methane

Answer 11

an example of radical substitution