Alkanes and fuels Flashcards Preview

Y12 MDY Organic Topic 2 - alkanes > Alkanes and fuels > Flashcards

Flashcards in Alkanes and fuels Deck (49)
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1
Q

A substances boiling point is a good indicator of what?

A

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

2
Q

What, in general, do high boiling points indicate?

A

High boiling points mean large intermolecular forces

3
Q

What are van der Waals forces?

A

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

4
Q

What are intermolecular forces?

A

They are forces between different molecules

5
Q

Are van der Waals forces strong or weak?

A

They’re the weakest.. boo hoo.

6
Q

What causes van der Waals forces to increase in alkanes?

A

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

7
Q

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

A

Straight chain

8
Q

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

A

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

9
Q

Describe the trend in the boiling points of the alkanes

A

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

10
Q

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

A

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

11
Q

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

A

Oxygen gas (O2)

12
Q

What do we mean by complete combustion?

A

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

13
Q

What is needed for complete combustion to occur?

A

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

14
Q

What are the products of complete combustion of a hydrocarbon?

A

carbon dioxide and water

15
Q

complete the equation:

alkane + oxygen →

A

alkane + oxygen → water + carbon dioxide​

16
Q

Why are alkanes used as fuels?

A

They burn exothermically

17
Q

What does exothermic mean?

A

Releases energy to the surroundings

18
Q

What could be a toxic gas product of incomplete combustion?

A

carbon monoxide, CO

19
Q

why is carbon monoxide toxic?

A

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

OR

you suffocate

OR

stops oxygen travelling around the body

20
Q

What is a solid product of incomplete combustion of alkanes?

A

soot

or

solid carbon

21
Q

What is incomplete combustion

A

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

22
Q

Why is carbon monoxide difficult to detect

A

it has no colour or odour

23
Q

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

A

C3H8(g) + 2 O2(g) → 4H2O(l) + 3C(s)​

24
Q

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

A

C3H8(g) + 7/2 O2(g) → 4H2O(l) + 3CO(g)​

25
Q

Soot can block engine parts.​

What problems can this cause?

Give 2 reasons

A
  • 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​
26
Q

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

A

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

27
Q

What is a greenhouse gas?

A

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

28
Q

Name 2 greenhouse gases

A
  • Carbon dioxide​
  • Hydrocarbons​
  • Water vapour​
  • Methane​
  • Nitrous oxide (N2O)​
29
Q

What is the greenhouse effect?

A

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.

30
Q

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

A
  • wastes fuel
  • harmful - carcinogenic
  • air pollutant - greenhouse gases
31
Q

How do you remove unburnt hydrocarbons from a cars exhaust?

A

Use a catalytic convertor

32
Q

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

A

NO (nitrogen monoxide) ​

33
Q

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

A

carbon dioxide

water

nitrogen gas (N2)

34
Q

What gases are normally found in the atmosphere?

A

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

35
Q

How is SO2 produced when hydrocarbons are burnt?

A

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

36
Q

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

A

S + O2 → SO2

37
Q

What kind of oxide is Sulphur Dioxide?

A

acidic oxide

38
Q

How does sulphur dioxide cause acid rain?

A

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

39
Q

Why does sulphur dioxide cause problems when fuel is burnt?

A

It is toxic

can cause respiratory problems​

causes acid rain

40
Q

How is the effect of sulphur in fuels reduced?

A

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

41
Q

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

A

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

42
Q

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

A

sulphur dioxide is an acid; the calcium compounds are bases

43
Q

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

A

Acid-base or neutralisation.

44
Q

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

A

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

Gypsum can make plasterboard

45
Q

How is nitrogen oxide formed in a car engine?

A

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

This causes N2(g) from the air to react with O2(g) .

46
Q

Why are nitrogen oxides removed from exhaust gases?

A

They can cause acid rain; greenhouse effect

47
Q

Whats the equation for the reaction in a catalytic convertor?

A

2CO+2NO → 2CO2 +N2

48
Q

What elements act as the catalyst in a catalytic convertor?

A

Platinum - Pt

Rhodium - Rh​

Palladium - Pd

49
Q

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

A

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