Alkanes

Question 1

What is a saturated hydrocarbon?

Answer 1

Contains no C=C or C to carbon triple bonds.

Question 2

What elements do hydrocarbons contain?

Answer 2

Contains hydrogen and carbon only.

Question 3

What does substitution mean in chemistry?

Answer 3

Replacing one atom or group with a different atom or group.

Question 4

What is homolytic fission?

Answer 4

Bond breaking in which one of the shared electrons goes to each atom.

Question 5

What is heterolytic fission?

Answer 5

Bond breaking in which both electrons in the shared pair go to a single atom.

Question 6

What is a radical in chemistry?

Answer 6

A particle with an unpaired electron.

Question 7

What is the boiling point of alkanes related to?

Answer 7

The boiling points are related to the length of the carbon chain and the amount of branching.

Question 8

What forces are responsible for the attraction between alkane molecules?

Answer 8

Van der Waals forces

These forces increase with longer carbon chains due to more electrons.

Question 9

How does molecular branching affect the boiling point of alkanes?

Answer 9

More branching leads to lower boiling points due to greater distance between molecules and weaker Van der Waals forces.

Increased branching results in fewer points of contact.

Question 10

What is the impact of alkane combustion on atmospheric carbon dioxide levels?

Answer 10

The percentage of carbon dioxide has risen from 0.03% to 0.04% due to the combustion of organic compounds.

This rise is believed to contribute to global warming.

Question 11

What products are formed from the complete combustion of hydrocarbons? Give the equation for the complete combustion of butane

Answer 11

Carbon dioxide and water.
C4H10 + 1302 goes to 4CO2 + 5H2O

This occurs when sufficient oxygen is present.

Question 12

What can result from incomplete combustion of hydrocarbons?
Give the equation for the incomplete combustion of methane

Answer 12

Formation of carbon (soot) and/or carbon monoxide.
CH4(g) + 3O2(g) goes to CO2(g) +2H2O(g)

This occurs when there isn’t enough oxygen present.

Question 13

What color flame indicates complete combustion of hydrocarbons?

Answer 13

Blue flame.

Complete combustion is more likely to produce a blue flame.

Question 14

What happens to the likelihood of complete combustion as the number of carbon atoms in a hydrocarbon increases?

Answer 14

The likelihood of complete combustion decreases.

Larger hydrocarbons are more likely to produce a yellow, smoky flame.

Question 15

Fill in the blank: The boiling point increases with the length of the _______.

Answer 15

carbon chain.

Question 16

True or False: More branched alkanes have higher boiling points.

Answer 16

False.

More branching leads to lower boiling points.

Question 17

What do bigger hydrocarbons burn with

Answer 17

A yellow smoky flame

Question 18

What is Carbon Monoxide (CO)?

Answer 18

A poisonous gas from incomplete combustion that prevents haemoglobin from bonding with oxygen

Carbon Monoxide is a significant health hazard, particularly in enclosed spaces.

Question 19

What are Nitrogen Oxides (NO, NO2, N2O4 or NOx)?

Answer 19

Gases that form nitric acid in air, creating acid rain and photochemical smog; formed from N2 and O2 when combined under high pressure

NOx emissions are a major contributor to air pollution and respiratory problems.

Question 20

What is Sulphur Dioxide (SO2)?

Answer 20

A gas that forms sulphuric acid, creating acid rain; formed from impurities containing sulphur in crude oil

SO2 can lead to respiratory issues and environmental damage.

Question 21

What are Carbon Particulates (C)?

Answer 21

Particles that trigger asthma and can lead to lung cancer; formed by incomplete combustion

Carbon particulates are a major concern for air quality and public health.

Question 22

What are Unburnt Hydrocarbons?

Answer 22

Compounds that create photochemical smog; formed by incomplete combustion

Unburnt hydrocarbons contribute to ozone formation at ground level, which is harmful to health.

Question 23

What is Carbon Dioxide (CO2)?

Answer 23

A greenhouse gas produced through combustion

CO2 is a significant contributor to climate change.

Question 24

What is Water Vapour (H2O) in the context of combustion?

Answer 24

A greenhouse gas produced through combustion

Water vapour plays a role in the natural greenhouse effect.

Question 25

What is the primary function of a catalytic converter?

Answer 25

To reduce carbon monoxide, nitrogen oxides, and hydrocarbons in exhaust emissions ## Footnote A catalytic converter transforms harmful exhaust gases into less toxic products.

Question 26

What materials are used to coat the inside surfaces of the honeycomb in a catalytic converter?

Answer 26

* Palladium (Pd) * Rhodium (Rh) * Platinum (Pt) ## Footnote These metals act as catalysts in the conversion process.

Question 27

What type of catalyst is used in a catalytic converter?

Answer 27

Three-way catalyst ## Footnote It catalyzes three types of reactions: oxidation of carbon monoxide, reduction of nitrogen oxides, and combustion of unburnt hydrocarbons.

Question 28

What is the reaction equation for the oxidation of carbon monoxide in a catalytic converter?

Answer 28

2CO + O2 → 2CO2 ## Footnote This reaction converts carbon monoxide into carbon dioxide.

Question 29

What is the reaction equation for the reduction of nitrogen oxides in a catalytic converter?

Answer 29

2NOx → N2 + xO2 ## Footnote This reaction reduces nitrogen oxides into nitrogen and oxygen.

Question 30

What is the general reaction for the combustion of unburnt hydrocarbons in a catalytic converter?

Answer 30

hydrocarbon + oxygen → carbon dioxide + water ## Footnote This reaction converts unburnt hydrocarbons into carbon dioxide and water.

Question 31

What is chemisorption?

Answer 31

The bonding of exhaust gases to metal particles in a catalytic converter ## Footnote Chemisorption weakens the bonding within the reactants and facilitates the reaction.

Question 32

How does chemisorption aid in the catalytic process?

Answer 32

It brings reactants closer together and arranges them in the correct orientation ## Footnote This increases the likelihood of the reaction occurring.

Question 33

What happens to carbon dioxide after it is formed in the catalytic converter?

Answer 33

It desorbs from the surface of the metal catalyst ## Footnote The metal catalyst remains unchanged by the reaction.

Question 34

What is heterogeneous catalysis?

Answer 34

A reaction in which the catalyst is in a different physical state than the reactants ## Footnote In a catalytic converter, the metal catalyst is solid while the reactants are gases.

Question 35

How does the ceramic honeycomb in a catalytic converter improve efficiency?

Answer 35

It creates a larger surface area for exhaust gases to contact the metal catalyst ## Footnote This maximizes the interaction between exhaust gases and the catalyst.

Question 36

When the bond is broken in a chlorine molecule why does homolytic fission occur

Answer 36

There’s no difference in electronegativity

Question 37

When the bond is broken in Hydrogen bromide why does heterolytic fission occur

Answer 37

There is a difference in electronegativity so the bromine attracts the electrons more

Question 38

What type of reaction is the halogenation of alkanes?

Answer 38

Photochemical reaction ## Footnote The reaction requires light absorption for it to occur.

Question 39

What role does light play in the halogenation of alkanes?

Answer 39

Provides energy needed for the reaction ## Footnote Light is consumed by the reaction and cannot be considered a catalyst.

Question 40

In the presence of ultraviolet light what is produced when a halogen substitutes a hydrogen in an alkane?

Answer 40

Halogenoalkane and hydrogen halide ## Footnote Example reaction: C6H14 + Br2 → C6H13Br + HBr.

Question 41

What is the first step in the mechanism of free radical substitution?

Answer 41

Initiation ## Footnote Involves the absorption of UV light energy to break bonds in halogen.

Question 42

What occurs during the initiation step?

Answer 42

Bond in the halogen breaks, forming free radicals ## Footnote This is done through homolytic fission.

Question 43

What is represented by a dot in the free radical mechanism?

Answer 43

An unpaired electron ## Footnote Free radicals have odd numbers of electrons.

Question 44

What is the reaction of chlorine gas under UV light?

Answer 44

Cl2 → Cl•+ Cl• ## Footnote This reaction produces free radicals.

Question 45

What are curly arrows used to represent in the propagation step?

Answer 45

Movement of electrons ## Footnote Double headed arrows represent a pair of electrons, single headed arrows represent a single electron.

Question 46

Complete the reaction: •Cl+ CH4 → ______.

Answer 46

•CH3 + HCl ## Footnote This step shows the formation of a methyl free radical.

Question 47

Complete the reaction: •CH3 + Cl2 → ______.

Answer 47

CH3Cl + •Cl ## Footnote This step shows the formation of chloromethane and another free radical.

Question 48

What is the reaction for the formation of chlorine gas of two chlorine radicals in termination

Answer 48

Cl• + Cl• → Cl2

Question 49

What is the reaction for the formation of alkenes from ethane radicals in termination

Answer 49

•CH3 + •CH3 → CH3-CH3

Question 50

What is the reaction of methane radicals with chlorine radicals in termination

Answer 50

•Cl + •CH3 → CH3Cl

Question 51

What are the undesirable products formed in the termination steps of chloromethane reactions?

Answer 51

* Ethane * Hydrogen chloride

Question 52

What products can chloromethane react to form with more chlorine radicals?

Answer 52

* CH2Cl2 * CHCl3 * CCl4

Question 53

Fill in the blank: The reaction •Cl + •Cl → _______ produces chlorine gas.

Answer 53

Cl2

Question 54

True or False: The termination steps produce only desirable products.

Answer 54

False