Chemical Reactions of The Alkanes

Question 1

Why are alkanes not very reactive?

Answer 1

The sigma bonds are strong.
The C-C bonds are non-polar
The carbon and hydrogen bonds have electronegativities so similar that they are considered non-polar.

Question 2

What do all alkanes react with to produce carbon dioxide and water?

Answer 2

A plentiful supply of oxygen.

Question 3

Why are alkenes used as fuel?

Answer 3

They are available, easy to transport and burn without releasing toxic products.

Question 4

What are the reactants in combustion?

Answer 4

An alkane and oxygen.

Question 5

What are the products of combustion complete combustion?

Answer 5

Carbon dioxide and water.

Question 6

What is the one thing that always has one mole in combustion?

Answer 6

The alkane.

Question 7

What are the products of incomplete combustion?

Answer 7

CO, CO2, H2O, C

Question 8

When does incomplete combustion occur?

Answer 8

When there is not enough oxygen.

Question 9

What is required in order for alkanes to react with halogens?

Answer 9

UV light

Question 10

Why is UV light needed in the reaction of alkanes with halogens?

Answer 10

To provide the initial energy for the reaction.

Question 11

What type of reaction is the reaction of alkanes with alkenes?

Answer 11

Substitution

Question 12

What is the mechanism for the bromination of alkanes called?

Answer 12

Radical substitution.

Question 13

What are the three stages for radical substitution?

Answer 13

Initiation
Propagation
Termination

Question 14

What happens in the initiation step?

Answer 14

The covalent bond in a bromine molecule is broken by homolytic fission.

Question 15

What is formed in the initiation step?

Answer 15

Two bromine radicals.

Question 16

Where does the energy for bond fission come from in initiation?

Answer 16

The UV light.

Question 17

What happens in the propagation stage?

Answer 17

A chain reaction

Question 18

How many equations are used to show propagation?

Answer 18

2

Question 19

What should always be different when constructing a propagation equation?

Answer 19

The reactant radical should be different to the product radical.

Question 20

What radical should be used for the second propagation equation?

Answer 20

The product radical from the first equation.

Question 21

In theory, when does the propagation stage end?

Answer 21

When the products run out.

Question 22

In practice, when does propagation end?

Answer 22

When two radicals collide.

Question 23

What happens in the termination step?

Answer 23

The two radicals collide.

Question 24

What is formed in the termination step?

Answer 24

A molecule with all electrons paired.

Question 25

How many possible termination steps are there?

Answer 25

This depends on the amount of radicals involved in the propagation step.

Question 26

Why does the reaction stop when both radicals collide?

Answer 26

They react and are therefore removed from the reaction mixture.