AQA A level Chemistry 3.3.2 Alkanes

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47 Terms

1

What is the general formula for alkanes? (1)

CnH2n+2

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2

How reactive are alkanes? (2)

- Alkanes are very unreactive

- But can burn in oxygen and react with halogens to produce halogenoalkanes

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3

How does the boiling point of alkanes change with carbon chain length? (1)

The longer the carbon chain, the higher the boiling point due to stronger van der Waals' forces

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4

How does branching in alkane isomers affect their boiling point? (3)

- More branching lowers the boiling point

- Due to weaker van der Waals' forces

- And less surface area contact between molecules

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5

What is crude oil? (3)

- Crude oil is a complex mixture consisting mainly of alkanes

- Crude oil has no use in its raw form

- So it must be separated by fractional distillation to provide useful products

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6

What is distillation? (1)

A method used to separate mixtures of miscible liquids based on differences in boiling points

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7

What determines the height at which a molecule condenses during fractional distillation? (2)

- The boiling point of the molecule determines the height

- Molecules with higher boiling points condense lower down in the column

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8

What is a fraction in fractional distillation? (1)

A fraction is a mixture of hydrocarbons with similar boiling points

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9

Draw the apparatus used for fractional distillation. (3)

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10

What happens to hydrocarbons as the carbon chain gets longer? (4)

- They become more viscous

- Harder to ignite

- Less volatile

- Have higher boiling points

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11

What is cracking? (1)

Cracking is the breaking of long-chain molecules into smaller ones

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12

Why is industrial cracking used? (2)

- To develop saturated and unsaturated hydrocarbon chains

- To meet the demand for shorter hydrocarbons like naphtha

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13

What does "saturated" mean in the context of hydrocarbons? (1)

Saturated hydrocarbons contain only single bonds

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14

What does "unsaturated" mean in the context of hydrocarbons? (1)

Unsaturated hydrocarbons contain double bonds (at least one C=C)

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15

What does "hydrocarbon" mean? (1)

A hydrocarbon contains only carbon and hydrogen atoms

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16

What are the conditions for thermal cracking? (1)

High temperature (~1000K) and high pressure (~7000kPa)

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17

What products are formed during thermal cracking? (1)

A high percentage of alkenes and straight-chain alkanes

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18

What are the conditions for catalytic cracking? (1)

Lower temperature (~720K) and the use of a catalyst, such as zeolite crystals

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19

What products are formed during catalytic cracking? (1)

Motor fuels, aromatic hydrocarbons, and cycloalkanes

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20

Write the equation for the cracking of one molecule of octane (C8H18) to form hexane (C6H14) and one other product. (1)

C8H18 → C6H14 + C2H4

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21

What is complete combustion of alkanes? (1)

Complete combustion occurs when alkanes react with excess oxygen to produce carbon dioxide and water

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22

How should combustion equations be balanced? (2)

- Combustion equations should be balanced alphabetically

- Carbon (C), Hydrogen (H), then Oxygen (O)

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23

What are the products of complete combustion of methane? (1)

The products are carbon dioxide (CO₂) and water (H₂O)

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24

Write the balanced equation for the complete combustion of methane. (1)

CH₄ + 2O₂ → CO₂ + 2H₂O

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25

What happens during incomplete combustion of alkanes? (1)

Incomplete combustion produces carbon monoxide (CO) or carbon (C) due to a limited supply of oxygen

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26

Write the balanced equation for incomplete combustion of methane producing carbon monoxide. (1)

CH₄ + 1.5O₂ → CO + 2H₂O

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27

Write the balanced equation for incomplete combustion of methane producing carbon. (1)

CH₄ + O₂ → C + 2H₂O

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28

How is carbon monoxide formed, and what problem does it cause? (2)

- The incomplete combustion of carbon-containing fuels

- It is toxic

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29

How are carbon particulates formed, and what problems do they cause? (2)

- Formed by the incomplete combustion of carbon-containing fuels

- They blacken buildings, cause respiratory problems, and contribute to global dimming

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30

How can the problem of carbon monoxide and carbon particulates be reduced? (1)

Ensure a good supply of oxygen when burning fuels

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31

What problem does carbon dioxide cause? (1)

Global warming

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32

How can the problem of carbon dioxide be reduced? (1)

Burn fewer fossil fuels

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33

How is sulfur dioxide formed, and what problem does it cause? (2)

- Sulfur dioxide is formed by the combustion of sulfur-containing compounds in fuels

- It reacts with water to form acid rain

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34

How can the problem of sulfur dioxide be reduced? (1)

Remove sulfur from fuel before burning or use flue gas desulfurization

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35

How are nitrogen oxides (NOₓ) formed, and what problem do they cause? (3)

- Nitrogen oxides are formed by the reaction of N₂ in the air with O₂

- At very high temperatures (e.g., in engines and furnaces)

- They react with water to form acid rai

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36

How can the problem of nitrogen oxides (NOₓ) be reduced? (1)

Use catalytic converters in cars

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37

How is water vapour formed, and what problem does it cause? (2)

- Formed by the combustion of fuels containing hydrogen

- It is a greenhouse gas

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38

What does flue gas desulfurisation remove from fossil-fuel power plant emissions? (1)

Flue gas desulfurisation removes SO₂ from the gases emitted by fossil-fuel power plants

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39

What substances are used in flue gas desulfurisation to neutralise sulfur dioxide? (1)

- CaO (calcium oxide) or CaCO₃ (calcium carbonate)

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40

Write the balanced chemical equation for flue gas desulfurisation using CaO. (1)

CaO(s) + SO₂(g) → CaSO₃(s)

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41

What harmful effect does sulfur dioxide cause if not removed from emissions? (1)

Sulfur dioxide causes acid rain

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42

What is the primary function of catalytic converters in cars? (2)

- Catalytic converters reduce the amount of CO, NO, and particulates

- That are released into the atmosphere by the engine

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43

What metals are typically used in the coating of catalytic converters? (3)

- Platinum

- Palladium

- Rhodium

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44

How does the honeycomb structure of catalytic converters improve their effectiveness? (1)

- The honeycomb structure increases the surface area

- Making the converter more cost-effective and efficient

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45

Write the balanced chemical equation for the reaction that occurs in a catalytic converter to reduce nitrogen oxides. (1)

2CO + 2NO → 2CO₂ + N₂

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46

Why is the ceramic material in catalytic converters essential? (1)

The ceramic material can withstand high temperatures inside the combustion engine.

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47

Write the overall reaction for the conversion of CO, NO, and hydrocarbons (C₈H₁₈) in a catalytic converter. (1)

C₈H₁₈ + 25NO → 8CO₂ + 12.5N₂ + 9H₂O

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