Alkanes and fuels

Question 1

A substances boiling point is a good indicator of what?

Answer 1

The boiling point of a substance is a good indication of the strength of forces between the particles in it.

Question 2

What, in general, do high boiling points indicate?

Answer 2

High boiling points mean large intermolecular forces

Question 3

What are van der Waals forces?

Answer 3

Van der Waals forces are a weak form of intermolecular force caused by electrons creating instantaneous dipole–induced dipole forces.

Question 4

What are intermolecular forces?

Answer 4

They are forces between different molecules

Question 5

Are van der Waals forces strong or weak?

Answer 5

They’re the weakest.. boo hoo.

Question 6

What causes van der Waals forces to increase in alkanes?

Answer 6

van der Waals forces increase with increasing numbers of electrons/increasing chain length.

Question 7

What will have the highest boiling point, a straight chain alkane or a branched chain alkane?

Answer 7

Straight chain

Question 8

Why do straight chain alkanes have the biggest boiling point compared to branched chains?

Answer 8

Van der Waals forces are highest when molecules have lots of surface contact. Straight chain molecules can pack closer so have more surface contact.

Question 9

Describe the trend in the boiling points of the alkanes

Answer 9

the boiling point increases as the length of the carbon chain increases

Question 10

Why does the boiling point of alkanes increase as the number of carbon atoms in the main chain increase?

Answer 10

The intermolecular (van der Waals) forces increase with increasing numbers of electrons/increasing chain length.

Question 11

What do all alkanes react with when they burn in air?

Answer 11

Oxygen gas (O₂)

Question 12

What do we mean by complete combustion?

Answer 12

There is enough oxygen gas for all the carbon and hydrogen in the hydrocarbon to be fully oxidised.

OR

Products of burning the alkane are water and carbon dioxide

Question 13

What is needed for complete combustion to occur?

Answer 13

Complete combustion occurs in a plentiful supply of air/oxygen.​

Question 14

What are the products of complete combustion of a hydrocarbon?

Answer 14

carbon dioxide and water

Question 15

complete the equation:

alkane + oxygen →

Answer 15

alkane + oxygen → water + carbon dioxide​

Question 16

Why are alkanes used as fuels?

Answer 16

They burn exothermically

Question 17

What does exothermic mean?

Answer 17

Releases energy to the surroundings

Question 18

What could be a toxic gas product of incomplete combustion?

Answer 18

carbon monoxide, CO

Question 19

why is carbon monoxide toxic?

Answer 19

It binds irreversibly to haemoglobin and so stops oxygen being transported around the body.

OR

you suffocate

OR

stops oxygen travelling around the body

Question 20

What is a solid product of incomplete combustion of alkanes?

Answer 20

soot

or

solid carbon

Question 21

What is incomplete combustion

Answer 21

not enough oxygen/air for the hydrocarbon to fully oxidise to carbon dioxide and water.

Question 22

Why is carbon monoxide difficult to detect

Answer 22

it has no colour or odour

Question 23

Give an equation for the incomplete combustion of propane that has only a solid product and water only​

Answer 23

C₃H_8(g) + 2 O_2(g) → 4H₂O_(l) + 3C_(s)​

Question 24

Give an equation for the incomplete combustion of propane that has a toxic gaseous product and water only​

Answer 24

C₃H_8(g) + 7/2 O_2(g) → 4H₂O_(l) + 3CO_(g)​

Question 25

Soot can block engine parts.​

What problems can this cause?

Give 2 reasons

Answer 25

• Less energy given out by the fuel​
• Engine is less powerful ​
• Engine needs to burn more fuel to get the same energy​
• Increased costs due to need to use more fuel​

Question 26

Soot can contribute to global dimming. What is global dimming?

Answer 26

Global dimming is a reduction in sunlight reaching Earth’s surface caused by air pollution/soot.

Question 27

What is a greenhouse gas?

Answer 27

A gas that contributes to the greenhouse effect by absorbing infrared radiation

Question 28

Name 2 greenhouse gases

Answer 28

• Carbon dioxide​
• Hydrocarbons​
• Water vapour​
• Methane​
• Nitrous oxide (N₂O)​

Question 29

What is the greenhouse effect?

Answer 29

The greenhouse effect is the process by which radiation from a planet’s atmosphere warms the planet’s surface to a temperature above what it would be without its atmosphere.

Question 30

Some hydrocarbon fuels can pass through the engine unburnt.​ Why are they a problem?

Answer 30

• wastes fuel
• harmful - carcinogenic
• air pollutant - greenhouse gases

Question 31

How do you remove unburnt hydrocarbons from a cars exhaust?

Answer 31

Use a catalytic convertor

Question 32

What gas do unburnt hydrocarbons react with in a catalytoc convertor?

Answer 32

NO (nitrogen monoxide) ​

Question 33

What are the products of unburnt hydrocarbons reacting with NO in a catalytic convertor?

Answer 33

carbon dioxide

water

nitrogen gas (N₂)

Question 34

What gases are normally found in the atmosphere?

Answer 34

Nitrogen (N₂), Oxygen (O₂), Carbon Dioxide (CO₂), Rare gases (Group 0)

Question 35

How is SO₂ produced when hydrocarbons are burnt?

Answer 35

Some fossil fuels contain sulphur as an impurity which reacts with oxygen

Question 36

Give an equation for the combustion of the sulphur that is contained in a fuel.​

Answer 36

S + O₂ → SO₂​

Question 37

What kind of oxide is Sulphur Dioxide?

Answer 37

acidic oxide

Question 38

How does sulphur dioxide cause acid rain?

Answer 38

This is an acidic oxide and can react with water to form acid rain.

Question 39

Why does sulphur dioxide cause problems when fuel is burnt?

Answer 39

It is toxic

can cause respiratory problems​

causes acid rain

Question 40

How is the effect of sulphur in fuels reduced?

Answer 40

Sulfur is usually removed from the fuel before burning; or SO₂ is removed from fumes after burning.

Question 41

How is SO₂ removed from waste gases after it is burnt?

Answer 41

React with calcium oxide (CaO) or calcium carbonate (CaCO₃)

Question 42

Why does sulphur dioxide react with calcium oxide/calcium carbonate?

Answer 42

sulphur dioxide is an acid; the calcium compounds are bases

Question 43

What kind of reaction is sulphur dioxide reacting with calcium oxide?

Answer 43

Acid-base or neutralisation.

Question 44

What is the product of calciumoxide and sulphur dioxide reacting? What can it be used for?

Answer 44

The reaction forms gypsum [calcium sulfate(IV), CaSO₃.​

Gypsum can make plasterboard

Question 45

How is nitrogen oxide formed in a car engine?

Answer 45

There are sparks and very high temperatures in an engine.​

This causes N_2(g) from the air to react with O_2(g) .

Question 46

Why are nitrogen oxides removed from exhaust gases?

Answer 46

They can cause acid rain; greenhouse effect

Question 47

Whats the equation for the reaction in a catalytic convertor?

Answer 47

2CO+2NO → 2CO₂ +N₂​

Question 48

What elements act as the catalyst in a catalytic convertor?

Answer 48

Platinum - Pt

Rhodium - Rh​

Palladium - Pd

Question 49

Why do catalytic converters have a ceramic honeycomb coated with a thin layer of catalyst?

Answer 49

This is cheaper (thin layer) and gives a large surface area (so faster reaction).