Hydrocarbons

Question 1

Fossil fuel

Answer 1

one that is derived from organisms that lived long ago

Question 2

Non-renewable resources

Answer 2

cannot be reformed in a reasonable timescale

Question 3

Greenhouse gas

Answer 3

causes increase in earths temp

Question 4

ó bonds

Answer 4

made by end to end overlap of s or p orbitals

Question 5

Complete combustion

Answer 5

combustion that occurs with excess oxygen

Question 6

Incomplete combustion

Answer 6

Combustion that occurs with insufficient oxygen

Question 7

halogenation

Answer 7

Reaction with any halogen and an organic compound

Question 8

Initiation

Answer 8

Reaction that starts a process. Molecule is turned into 2 radicals

Question 9

homolytic bond fission

Answer 9

When a bond is broken and each of the bonded atoms receives one of the bond electrons

Question 10

Radical

Answer 10

Species with an unpaired electron
Highly reactive and they react indiscriminately to gain another electron to form an electron pair

Question 11

Propagation

Answer 11

Reaction by which the process continues
Molecule reacts with a radical to make a new molecule and a new radical

Question 12

Chain reaction

Answer 12

One that involves a series of steps and, once started, continues

Question 13

Termination

Answer 13

Reaction that ends the process
Two radicals react to make a molecule

Question 14

Reaction mechanism

Answer 14

Shows the stages by which a reaction proceeds

Question 15

Substitution reaction

Answer 15

One in which one atom/group is replaced by another atom/group

Question 16

Pi bond

Answer 16

One formed by sideways overlap of P orbitals

Question 17

E-Z isomers

Answer 17

Isomerism that occurs in alkenes due to restricted rotation about the double bond

Question 18

Electrophile

Answer 18

Electron deficient species that can accept an lone pair of electron

Question 19

heterolytic bond fission

Answer 19

When a bond is broken and one of the bonded atoms receives both electrons from the covalent bond. Ions are formed

Question 20

Addition reaction

Answer 20

A reaction in which reagents combine to give only one product

Question 21

Carboncation

Answer 21

An ion with a positively charged carbon atom

Question 22

Polymerisation

Answer 22

Joining of a very large number of monomer molecules to make a long chain polymer molecule

Question 23

Monomer

Answer 23

Small molecule that can be made into a polymer

Question 24

Repeat unit

Answer 24

Section of a polymer that is repeated to make a whole structure

Question 25

Advantages of fossil fuels

Answer 25

• Available in a variety of forms so type of feel can be matched with its use
• Available at all times
• Currently widely available and current infrastructure is generally set up around the use of them

Question 26

Disadvantages of fossil fuels

Answer 26

• Non renewable
• Combustion of fossil fuels produces carbon dioxide: greenhouse gas- Absorb infrared radiation from the Earth’s surface then emitted in all directions
• acid rain
• carbon monoxide

Question 27

alkanes structure
And properties

Answer 27

• General formula CnH2n+2
• Saturated hydrocarbons
• Properties vary as the relative molecular mass increases
  Small alkanes or gases in room temperature, larger are liquids
• Burn by reaction with oxygen, reaction is exothermic

Question 28

Products when hydrocarbons undergo complete combustion

Answer 28

Water and carbon dioxide ( If sufficient oxygen is present)

Question 29

Write a balanced chemical equation for the complete combustion of ethane

Answer 29

2C(2)H(6) + 7O(2) → 4CO(2) + 6H(2)O

Question 30

When does incomplete combustion occur? What is required to ensure complete combustion occurs?

Answer 30

Incomplete combustion occurs when there is an insufficient supply of oxygen.
To ensure complete combustion occurs, the reaction should be carried out with excess oxygen.

Question 31

Compare the difference in reactivity of alkanes and alkenes

Answer 31

Alkenes have a high electron density in the carbon-carbon double bond, C=C. This makes them more susceptible to attacks from electrophiles, compared to alkanes, making alkenes more reactive.

Question 32

Halogenation process

Answer 32

Alkanes do not react with halogens in the dark but if exposed to UV light they will

Question 33

Initiation stage 1

Answer 33

UV light has sufficient energy to break the cl - cl bond homolytically
Cl2—-> 2Cl*

Question 34

Propagation stage 2

Answer 34

Uses a radical as a reactant then forms a radical as a product
Means reaction continues- chain reaction
Cl* + CH4—–> CH3* +HCI
CH3* + Cl2—-> CH3Cl +Cl*

Question 35

Termination stage 3

Answer 35

Propagation steps continue until radicals meet then reaction stops
Cl* +CH3* —-> CH3Cl

Question 36

Radical reactions are hard to control

Answer 36

For the substitution reactions occur meaning a mixture of products will be formed
Make this an unsatisfactory method for making a high yield of a specific halogenalkane
Can be avoided if amounts of halogen use is very limited

Question 37

structure of alkenes

Answer 37

• Unsaturated hydrocarbons
  General formula CnH2n

Question 38

How alkenes are formed

Answer 38

Formed when petroleum is cracked and although they undergo combustion they will not be generally used as fuels
Important as the starting material for organic synthesis reactions eg. Polymerisation

Question 39

Ethene

Answer 39

• each C has structure 1s2,2s2, 2p2 ( each as 4 electrons for bonding)
• 3 ‘normal’ covalent bonds formed using 3 electrons
• Bonds called ō bonds, Involve both s electrons and one p electron in each C

Question 40

P orbitals in ethene

Answer 40

1 p orbital electron on each C is not used to form the bonds
P orbitals overlap sideways producing pi bond- Area of high electron density above and below the plane of a molecule
Restricted movement about double bonds is due to pi bond
Meaning many alkenes exist as E-Z isomers

Question 41

Properties of E-Z isomers

Answer 41

• In general the shape of E molecules mean that they can fit together more closely and have stronger intermolecular forces therefore higher Mt.

Question 42

Electrophilic addition reactions

Answer 42

An electrophile is any species that can accept a lone pair of Electrons
Mechanism of reaction involves heterolytic bond vision leading overall to an addition reaction

Question 43

Stability of a carboncation

Answer 43

The most stable a carbocation is the more likely it will form
The positive ion is more stable in reaction one than in reaction two because alkll groups tend to release electrons so that they become S+
Spreads or delocalises positive charge and stabilises the iron meaning secondary carbocations are more stable than primary

Question 44

Testing for alkenes

Answer 44

• Reaction with bromine
  Brown bromine water to clear
  Liquid bromine can be very corrosive

Or decoloration of purple acidified potassium maganate

Question 45

Factional distillation- why are different fractions different boiling temperatures

Answer 45

Boiling temperatures increase with increase in chain length
More carbon atoms result in an increase in Van der waals forces

Question 46

How can fractional distillation be carried out

Answer 46

Petroleum is heated and evaporated
Fractions condense at different temperatures They are separated with different bOiling temperatures