Alkanes

Question 1

Are alkanes polar?

Answer 1

They are non-polar

Question 2

What intermolecular forces are present in alkanes?

Answer 2

Only van der Waals

Question 3

Why are alkanes non-polar

Answer 3

The electronegativity difference between C and H is very small

Question 4

What is the general formula of an Alkane?

Answer 4

CnH2n+1

Question 5

What is the shape and bond angle of an alkane?

Answer 5

Tetrahedral, 109.5

Question 6

What is the trend in boiling point and the chain length of an alkane increases, and why?

Answer 6

As chain length increases, the strength of the van der Waals forces increases

Question 7

What is the difference in boiling points between branched and straight alkanes?

Answer 7

Branched alkanes have lower boiling points than straight alkanes due to reduced surface area.

Question 8

Are alkanes soluble?

Answer 8

Alkanes are insoluble in water, but soluble in non-polar solutions

Question 9

Are alkanes reactive?

Answer 9

Alkanes are relatively unreactive due to their strong C-H and C-C bonds

Question 10

Describe the process of fractional distillation

Answer 10

Crude oil is vaporised. Vapour passes into tower that is cooler at the top and hotter at the bottom. Vapour rises until it reaches a fraction that is at a temp lower than its boiling point, and condenses. Vapours are collected at separate fractions. Shorter hydrocarbons condense in fractions at the top. Tar/bitumen builds at the bottom, and is used for road surfacing

Question 11

What is cracking?

Answer 11

The break down of longer hydrocarbon chains to form shorter, more useful hydrocarbons

Question 12

What are the types of cracking?

Answer 12

Thermal and Catalytic

Question 13

What are the conditions of thermal cracking?

Answer 13

Heating alkanes to high temps (700-1200K), high pressure (up to 7000kPa)

Question 14

What does thermal cracking tend to produce more of?

Answer 14

High proportions of alkanes

Question 15

What are the conditions for catalytic cracking?

Answer 15

Lower temps (720K), lower pressure (but more than atmospheric pressure) and a zeolite catalyst

Question 16

What are properties of the zeolite cataylst

Answer 16

contains silicon dioxide and aluminosilicates, has a honeycomb structure with an enormous surface area, they are acidic.

Question 17

What are the main products formed from catalytic cracking

Answer 17

Branched alkanes, cycloalkanes, aromatic compounds

Question 18

What are the products formed from the incomplete combustion of alkanes?

Answer 18

Carbon monoxide (CO) and water (H2O)

Question 19

What is the impact of CO on the environment?

Answer 19

Poisonous gas

Question 20

What is the impact of NOx on the environment? How is it formed?

Answer 20

Forms nitric acid which causes acid rain and photochemical smog. Formed when petrol engines heat up to high enough temps that oxygen and nitrogen from the atmosphere can react.

Question 21

What is the impact of SO2 on the environment?

Answer 21

Causes acid rain when it is formed from impurities.

Question 22

What is the impact of carbon particles on the environment?

Answer 22

They can cause asthma and cancer.

Question 23

What is the impact of unburnt hydrocarbons on the environment?

Answer 23

They are a greenhouse gas

Question 24

What is the impact of CO2 and water vapour on the environment?

Answer 24

They are greenhouse gases.

Question 25

What do catalytic converters do?

Answer 25

They remove CO, NOx and unburnt hydrocarbons by reacting them with each other.

Question 26

Write the equation of the reaction of SO2 to form the H2SO4 that causes acid rain

Answer 26

SO2+1/2 O2 + H2O --> H2SO4

Question 27

What is the mechanism for the depletion of Ozone?

Answer 27

Free radical substitution

Question 28

Write the equations/mechanism for the depletion of Ozone

Answer 28

Cl* + O3 --> ClO* + O2 ClO* + O3 --> 2O2 +Cl*

Question 29

What is an alkane?

Answer 29

A saturated hydrocarbon

Question 30

What is petroleum?

Answer 30

A mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation

Question 31

What are the economic reasons for cracking?

Answer 31

The shorter chain products are economically more valuable than longer chain material. Cracking helps to meet the demand for the shorter chain hydrocarbons

Question 32

What can alkanes be used as?

Answer 32

They can be used as fuels

Question 33

What is flue gas desulfurisation?

Answer 33

The process of removing the sulfur dioxide from the flue gas released by power stations

Question 34

Explain the process of flue gas desulfurisation - Include overall reaction

Answer 34

A slurry of calcium oxide and water is sprayed onto the flue gas which reacts with the calcium oxide ad water to form calcium sulfite, which can be further oxidised to calcium sulfate. Overall reaction: CaO(s) + 2H2O(l) + SO2(g) +0.5O2 -> CaSO4.2H2O(s)

Question 35

What is the alternate flue gas desulfurisation method? without slurry spraying (include any equations)

Answer 35

Use calcium carbonate (limestone) rather than calcium oxide: CaCO3 + 0.5O2(g) +SO2(g) --> CaSO4(s) + CO2(g)

Question 36

What are the 3 stages of free radical substitution?

Answer 36

Initiation, propagation and termination

Question 37

What is initiation step in free radical substitution?

Answer 37

The formation of a free radical, eg the breaking of the bond in Cl-Cl

Question 38

Why does the C-H bond not usually break as the initiation step?

Answer 38

The C-H bond in an alkane needs more energy to break than is available in a quantum of ultraviolet radiation

Question 39

What is the first part of the propagation step in free radical substitution?

Answer 39

The free radical from the initiation reaction goes on to react with a normal compound, and form a normal compound, leaving behind a free radical, eg: Cl* + CH4 --> HCl + *CH3

Question 40

What is the second part of the propagation step in free radical substitution?

Answer 40

The free radical formed in the first part of propagation reacts with a different free radical, forming a normal compound, and leaving behind another free radical, e.g: *CH3 +Cl2 --> CH3Cl + Cl*

Question 41

What is the termination step in free radical substitution

Answer 41

This is the step where the free radicals are removed, when they react with each other, e.g: Cl* + Cl* --> Cl2

Question 42

How is sulfur dioxide formed from hydrocarbons?

Answer 42

The combustion of hydrocarbons containing sulfur leads to sulfur dioxide that causes air pollution