15.3 The Alkenes

Question 1

What is unsaturated hydrocarbon?

Answer 1

Compounds of hydrogen and carbon only molecules contain carbon to carbon double bonds or triple bonds

Question 2

What is cracking?

Answer 2

The process in which large less useful hydrocarbon molecules are broken down into smaller more useful molecules in an oil refinery

Question 3

Explain how the process of cracking takes place

Answer 3

The larger hydrocarbon molecules are fed into a steel chamber that contains no oxygen so combustion does not take place. The larger hydrocarbon molecules are heated to a high temperature and are passed over an aluminium oxide catalyst.

Question 4

When large alkane molecules are cracked, what is produced?

Answer 4

Smaller alkane molecules and alkane molecules

Question 5

Why are alkenes more reactive than alkanes?

Answer 5

Because of their double bonds

Question 6

Why does alkenes being more reactive make them very valuable

Answer 6

This makes them useful for the chemical industry as the starting compounds (feedstock) many new products. These include most plastics.

Question 7

What are some methods of making alkenes?

Answer 7

Cracking of alkanes
Elimination of a hydrogen halide from a halogen alkane by heating with ethanolic
Sodium hydroxide
Dehydration of an alcohol by using a heated catalyst (aluminium oxide) or a concentrated acid

Question 8

What is dehydration?

Answer 8

It is the elimination of a water molecule from a reactant molecule

Question 9

Most reactions of alkenes examples of

Answer 9

addition reactions

Question 10

What happens in the addition reaction of alkenes?

Answer 10

One of the two bones in the carbon to carbon double bonds is broken and a new single bond is formed from each of the two carbon atoms.

Question 11

What happens in the addition of hydrogen to an alkene

Answer 11

When hydrogen gas and an alkene are heated and passed over a finely divided platinum/nickel catalyst the addition reaction produces an alkane

Question 12

What is hydrogenation?

Answer 12

The addition reaction of alkenes with hydrogen

Question 13

Give one example when hydrogenation is used

Answer 13

In the manufacture of margarine

Question 14

What happens in the addition of alkenes to hydrogen halides

Answer 14

When an alkene is through a concentrated solution of hydrogen halide at room temperature the product is halogen alkane

Question 15

When are 2 possible products possible in the reaction of addition of hydrogen halides?

Answer 15

When there are longer asymmetric alkenes reacting with a hydrogen halide

Question 16

What is the major product when 2 addition products are possible in alkenes

Answer 16

The major product is the one that has the halogen atom bonded to the carbon to carbon double bond carbon atom with the highest number of alkyl groups bonded to it

Question 17

What is an intermediate in a reaction?

Answer 17

A species which is formed at a particular step of the reaction. Intermediate are stable enough to react with another substance but not enough to be a product..

Question 18

How is alcohol made in the industry?

Answer 18

By the addition of steam to gaseous alkenes high temperatures and pressure in the presence of concentrated phosphoric acid. H3PO4

Question 19

How is alcohol made in the industry?

Answer 19

By the addition of steam to gaseous alkenes high temperatures and pressure in the presence of concentrated phosphoric acid as a catalyst