Alkanes 2.3

Question 1

What is a saturated hydrocarbon?

Answer 1

A saturated hydrocarbon contains no C=C or C≡C.

Question 2

What elements are found in a hydrocarbon?

Answer 2

A hydrocarbon contains hydrogen and carbon only.

Question 3

What happens to the boiling points of alkanes as molecular mass increases?

Answer 3

The boiling points of alkanes increase with increasing molecular mass.

Question 4

What are the physical states of shorter chain alkanes at room temperature?

Answer 4

Shorter chain alkanes are gases at room temperature.

Question 5

What are the physical states of C5-C17 alkanes at room temperature?

Answer 5

C5-C17 alkanes are liquids at room temperature.

Question 6

What happens to van der Waals’ forces as relative molecular mass increases?

Answer 6

The van der Waals’ forces increase in strength due to the increasing number of electrons present.

Question 7

What happens to the boiling point of isomers with the same relative molecular mass as branching increases?

Answer 7

The boiling point decreases.

Question 8

What are alkanes generally known for?

Answer 8

Alkanes are generally unreactive.

Question 9

What forms when alkanes undergo combustion?

Answer 9

Alkanes produce carbon dioxide and water while under combustion

Question 10

What characterizes alkanes in terms of combustion?

Answer 10

Alkanes are characterised by having large enthalpies of combustion.

Question 11

What is a common use of alkanes?

Answer 11

Alkanes are used extensively as fuels.

Question 12

What pollutants are obtained when fuel is burnt in an engine?

Answer 12

The pollutants obtained are carbon dioxide, carbon monoxide, carbon, sulfur dioxide, and oxides of nitrogen.

Question 13

What is the main reaction occurring in an engine?

Answer 13

The main reaction is the combustion of the fuel.

Question 14

What reactions occur due to high pressure and temperature in the combustion chamber?

Answer 14

Nitrogen reacts with oxygen to form nitrogen oxides.

Question 15

What is the chemical reaction for nitrogen reacting with oxygen to form nitrogen monoxide?

Answer 15

N2 + O2 → 2NO

Question 16

What is the chemical reaction for nitrogen reacting with oxygen to form nitrogen dioxide?

Answer 16

N2 + 2O2 → 2NO2

Question 17

What does sulfur react with to form sulfur dioxide?

Answer 17

Sulfur reacts with oxygen to form sulfur dioxide.

Question 18

What are the environmental problems caused by sulfur dioxide?

Answer 18

Sulfur dioxide contributes to acid rain, global warming, and smog.

Question 19

What is acid rain?

Answer 19

Acid rain is rain that is more acidic than normal due to human activity.

Question 20

What is a major cause of acid rain?

Answer 20

The burning of fossil fuels that contain sulfur compounds is a major cause.

Question 21

What chemical reaction occurs when sulfur dioxide dissolves in water?

Answer 21

SO2 + H2O → H2SO3

Question 22

What does sulfurous acid oxidize to form?

Answer 22

Sulfurous acid is oxidized to form sulfuric acid (H2SO4).

Question 23

What are the effects of acid rain?

Answer 23

Acid rain defoliates and destroys trees, corrodes buildings, and kills fish.

Question 24

What is photochemical smog?

Answer 24

Photochemical smog is caused by toxic gases and minute solid particles suspended in air close to the Earth’s surface.

Question 25

How is photochemical smog formed?

Answer 25

It is formed when nitrogen oxides, sulfur dioxide, and unburned hydrocarbon fuels react with sunlight.

Question 26

What health problems can photochemical smog cause?

Answer 26

It can cause a variety of health problems, such as eye irritation, nasal congestion, and respiratory problems.

Question 27

What happens to electromagnetic radiation from the Sun when it reaches the Earth?

Answer 27

Some is reflected back into space, while the rest is absorbed and heats the Earth up.

Question 28

What is radiated from the Earth towards space?

Answer 28

Infrared radiation is radiated from the Earth towards space.

Question 29

Which gases are good at absorbing radiation and heating the atmosphere?

Answer 29

Gases such as water vapour, methane, and carbon dioxide.

Question 30

What is the greenhouse effect?

Answer 30

It is an important natural process where certain gases absorb radiation and heat the atmosphere up.

Question 31

Why is the greenhouse effect important for Earth?

Answer 31

Without it, the Earth would not be able to sustain life.

Question 32

What is the purpose of catalytic converters in petrol motor vehicles?

Answer 32

They reduce the environmental impact of pollutants by converting them to less harmful products.

Question 33

What are oxides of nitrogen converted to in catalytic converters?

Answer 33

They are reduced to nitrogen and oxygen. ## Footnote Reaction: 2NO → N2 + O2

Question 34

What happens to carbon monoxide in catalytic converters?

Answer 34

It is oxidised to carbon dioxide. ## Footnote Reaction: 2CO + O2 → 2CO2

Question 35

What is the combined reaction of oxides of nitrogen and carbon monoxide?

Answer 35

2NO + 2CO → N2 + 2CO2

Question 36

What is the structure of a catalytic converter?

Answer 36

It has a honeycomb structure coated with a thin layer of platinum and rhodium.

Question 37

Why is the thin coating on a catalytic converter important?

Answer 37

It keeps costs down while providing a large surface area for reactions.

Question 38

What effect does leaded petrol have on catalytic converters?

Answer 38

It stops the catalyst from working by coating the surface with lead, rendering the metal catalyst passive.

Question 39

What are alkanes?

Answer 39

Alkanes are hydrocarbons that can react with halogens to produce halogenoalkanes.

Question 40

What type of reaction do alkanes undergo with halogens?

Answer 40

Alkanes react with halogens via a photochemical free radical substitution reaction.

Question 41

What is substitution in chemistry?

Answer 41

Substitution is replacing one atom or group with a different atom or group.

Question 42

What is a radical?

Answer 42

A radical is a particle with an unpaired electron.

Question 43

What is the first step in the reaction of alkanes with halogens?

Answer 43

Step 1: Initiation ## Footnote The chlorine molecule absorbs UV light and the bond breaks symmetrically.

Question 44

What is homolytic fission?

Answer 44

Homolytic fission is bond breaking in which one of the shared electrons goes to each atom.

Question 45

What is heterolytic fission?

Answer 45

Heterolytic fission is bond breaking in which both electrons in the shared pair go to a single atom.

Question 46

What happens in the propagation step of the reaction?

Answer 46

In Step 2: Propagation, a chlorine radical reacts with a methane molecule, producing a methyl radical.

Question 47

What occurs during the termination step of the reaction?

Answer 47

In Step 3: Termination, the reaction slows down and stops as radicals collide and react together.

Question 48

What is the result of the reaction between alkanes and halogens?

Answer 48

The reaction forms a mixture of halogenoalkanes, as the product can react further until all hydrogen atoms on the alkane are substituted.