Module 1- Basic concepts and Hydrocarbons

Question 1

Define Hydrocarbons.

Answer 1

Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms.

Question 2

Define Unsaturated Hydrocarbons.

Answer 2

An Unsaturated hydrocarbon is a hydrocarbon contain carbon-to-carbon multiple bonds.

Question 3

Define an Aliphatic Hydrocarbon.

Answer 3

An Aliphatic hydrocarbon is an hydrocarbon with carbon atoms joined together in straight or branched chains.

Question 4

Define an Alicyclic Hydrocarbon.

Answer 4

An Alicyclic hydrocarbon is an hydrocarbon with carbons joined together in a ringed structure.

Question 5

What is meant by the term “A homologous series’?

Answer 5

A homologous series is a series of organic compounds with the same functional group but with each successive member differing by CH2.

Question 6

What is a Functional group?

Answer 6

A functional group is the part of the organic molecule responsible for its chemical reaction.

Question 7

What is an alkyl group?

Answer 7

An alkyl group is an alkane with a hydrogen atom removed.

Question 8

Name three stages in Free Radical substitution>

Answer 8

The three stages of free radical substitution are:

Initiation, Propagation and Termination.

Question 9

What happens during the initiation stage of free radical substitution?

Answer 9

The radicals are produced at this stage. It always involves the breaking of a covalent bond by UV radiation. Because two of the same radicals are formed by the splitting this is called homolytic fission.

Question 10

What happens during the propagation stage of free radical substitution.

Answer 10

This stage keep the reaction going because it produces radicals, making it a chain reaction.

Question 11

What happens during the termination stage of free radical substitution?

Answer 11

This ends the chain reaction because radicals are tied up. The products of chain reactions are difficult to predict because the reactions are difficult to control.

Question 12

Give five reasons why petrol is considered a “good fuel”?

Answer 12

Its vapour mixes easily with air/ oxygen and ignites at low temperatures.
as a liquid, it is easily transported and easy to store.
it leaves little or no residue after it is burned.
when it burns,it releases large amounts of energy and large volumes of gas that can drive a car piston.
the structures of the hydrocarbons in the petrol mixture can be altered to burn more smoothly.

Question 13

What are the three main types of fossil fuel.

Answer 13

The three main fossil fuels are coal,oil and natural gas.

Question 14

What is crude oil made up of?

Answer 14

Crude oil is mostly a mixture of alkanes with different boiling points.

Question 15

Explain the process of cracking.

Answer 15

Cracking uses a high temperature and a catalyst to break up longer chain alkane molecules in alkenes and either more useful alkanes and hydrogen. It is a type of thermal decomposition.

Question 16

Define Radical substitution.

Answer 16

Radical substitution is a type of substitution reaction in which a radical replaces a different atom or group of atoms.

Question 17

Define the term mechanism.

Answer 17

Mechanism is a sequence of steps showing the path of electrons in a reaction.

Question 18

Define the term initiation.

Answer 18

Initiation is the first step in a radical substitution in which the free radicals are generated by ultraviolet radiation

Question 19

Describe what happens in the first propagation step.

Answer 19

In the first propagation step, methane reacts with a chlorine radical. A single C-H bond is broken by homolytic fission forming a .CH3 methyl radical. Hydrogen chloride, HCl is also formed.

Question 20

Describe what happens in the second propagation step.

Answer 20

In the second propagation step, the methyl radical reacts with a chlorine molecule. The organic product is chloromethane is formed together with a further chlorine radical. The chlorine radical can be used again in the first propagation step.

Question 21

Define the term termination in relation to radical substitution.

Answer 21

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

Question 22

Describe what happens during the termination stage.

Answer 22

In the termination stage, two radicals combine to form a molecule. There are a number of possible termination steps. This is because of the large numbers of radicals in the reaction mixture.

Question 23

Define a pi-bond

Answer 23

A pi-bond is the reactive part of a double bond formed above and below the plane of bonded atoms by sideways overlap of p orbitals.

Question 24

Where is a sigma bond found in the formation of a double bond?

Answer 24

A sigma bond is formed directly between two carbon atoms by the overlap of orbitals. Each carbon contributes one electron to the electron pair in the sigma bond.

Question 25

Where is the pi-bond found in the formation of a double bond.

Answer 25

The pi-bond is formed above and below the plane of the carbon atoms by sideways overlap of p orbitals . Each carbon atom contributes one electron from a p- orbital to the electron pair in the pi bond.