A-LEVEL CHEMISTRY: 3.3.2: Alkanes (ChemRevise)

Question 1

What is ‘Petroleum’?

Answer 1

Petroleum is a Mixture consisting mainly of Alkane Hydrocarbons

Question 2

What is a ‘Fraction’?

Answer 2

a Fraction is a Mixture of Hydrocarbons with a similar Chain Length & Boiling Point

Question 3

Explain the process ‘Fractional Distillation Industrially’: (10)

Answer 3

-oil is pre-heated

-then passed into column

-the Fractions Condense at different heights

-the Temperature of the column decreases upwards

-the Separation depends of Boiling Point

-Boiling Point depends on size of Molecules

-the larger the Molecule, the larger the Van der Waals Forces

-similar sized Molecules Condense together

-small Molecules Condense at the top, at lower Temperatures

-big Molecules Condense at the bottom, at higher Temperatures

Question 4

Cracking:

Answer 4

Conversion of large Hydrocarbon Chains to smaller Hydrocarbon Molecules by breakage of C-C bonds

Question 5

Economic reasons for Cracking: (3)

Answer 5

-shorter Hydrocarbon Chains are in more demand

-makes use of otherwise useless long Hydrocarbon Chains

-the products of Cracking are more valuable than the starting materials

Question 6

2 main types of Cracking: (2)

Answer 6

-Thermal
-Catalytic

Question 7

Thermal Cracking Conditions: (2)

Answer 7

-High Pressure (~7000kPa)

-High Temperature (~400’C - 9000’C)

Question 7

Products of Thermal Cracking: (2)

Answer 7

-Produces mostly Alkenes

-Sometimes Produces Hydrogen

Question 8

Thermal Cracking Produces mostly ___.

Answer 8

Alkanes

Question 9

Thermal Cracking sometimes Produces ___.

Answer 9

Hydrogen

Question 10

Catalytic Cracking Conditions: (3)

Answer 10

-Slight/moderate Pressure

-High Temperature (~450’C)

-Zeolite Catalyst

Question 11

Products of Catalytic Cracking: (2)

Answer 11

-Branched Alkanes

-Aromatic Hydrocarbons

Question 12

Fuel:

Answer 12

Releases Heat Energy when Burnt

Question 13

Complete Combustion:

Answer 13

in excess Oxygen, Alkanes will Burn with Complete Combustion.

the Products of Complete Combustion are CO2 and H2O

Question 14

Products of Complete Combustion:

Answer 14

CO2 & H2O

Question 15

Complete Combustion occurs in…

Answer 15

Excess of Oxygen

Question 16

Incomplete Combustion:

Answer 16

Limited amount of Oxygen.
Produces CO (v. toxic) and/or C (soot)

Question 17

Products of Incomplete Combustion: (2)

Answer 17

CO (v. toxic) and/or C (soot)

Question 18

why are Alkanes used as Fuels?

Answer 18

Alkanes burn in the presence of Oxygen.
this Combustion is highly Exothermic.

Question 19

SO2 will dissolve in Atmospheric Water, and can Produce:

Answer 19

Acid Rain

Question 20

how can SO2 be removed from Waster Gas (to prevent acid rain)?

Answer 20

by Flue Gas Desulfurisation

Question 21

Pollutants from Combustion: (5)

Answer 21

-Nitrogen Oxides

-Carbon Monoxide (CO)

-Carbon Dioxide (CO2)

-Unburnt Hydrocarbons

-Soot (C)

Question 22

Environmental consequence of the Pollutant ‘Nitrogen Oxides’: (3)

Answer 22

-NO is toxic

-can form NO2 (Acidic Gas)

-Acid Rain

Question 23

Environmental consequence of the Pollutant ‘Carbon Monoxide’:

Answer 23

toxic

Question 24

Environmental consequence of the Pollutant 'Carbon Dioxide':

Answer 24

contributes towards global warming

Question 25

Environmental consequence of the Pollutant 'Unburnt Hydrocarbons':

Answer 25

contributes towards formation of smog

Question 26

Environmental consequence of the Pollutant 'Soot': (2)

Answer 26

-global dimming -respiratory problems

Question 27

Catalytic Converters:

Answer 27

remove CO, Nitrogen Oxides, & Unburned Hydrocarbons from vehicle exhaust gases, turning them into 'harmless' CO2, N2 & H2O

Question 28

Describe Catalytic Converters: (3)

Answer 28

-Ceramic -Honeycomb -thin layer of Catalyst Metals (Platinum, Palladium, Rhodium) to give Large Surface Area

Question 29

Greenhouse Gases: (3)

Answer 29

-Carbon Dioxide (CO2) -Methane (CH4) -Water Vapour (H2O)

Question 30

___ ___ passes through the Atmosphere to the Earth's Surface and ___ it up.

Answer 30

UV Radiation, Heats

Question 31

the Earth Radiates out ___ ___ ___ Radiation/

Answer 31

Infrared Long Wavelength

Question 32

Carbon Dioxide levels have risen significantly in recent years. why?

Answer 32

Increased Burning of Fossil Fuels

Question 33

In the presence of ___ ___, Alkanes React with Chlorine to form a Mixture of products with the Halogens substituting Hydrogen Atoms. The Mechanism for this Reaction is:

Answer 33

UV Light, Free Radical Substitution

Question 34

Steps of Free Radical Substitution: (3)

Answer 34

-Initiation -Propagation -Termination

Question 35

The ___ Light supplies the Energy to break the Cl-Cl bond. This process is called...

Answer 35

UV. Homolytic Fission

Question 36

Free Radical:

Answer 36

a Reactive species that has an Unpaired Electron

Question 37

As the Cl Free Radical is generated, it can react with several more Alkane Molecules in a...

Answer 37

Chain Reaction

Question 37

All Propagation steps have a ___ ___ in the ___ & ___.

Answer 37

Free Radical, Reactants & Products