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Chemistry A-level - Mr Donelly > Alkane Chemistry > Flashcards

Alkane Chemistry Flashcards

1
Q

What is the general formula for alkanes?

A

CnH2n+2

Examples include CH4 (methane) and C8H18 (octane)

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2
Q

What characterizes saturated hydrocarbons?

A

Every carbon atom has 4 single covalent bonds around it.

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3
Q

Why are alkanes considered non-polar?

A

No distinct dipole moment present in the molecules.

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4
Q

What is the solubility of alkanes in water?

A

Not water soluble.

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5
Q

What makes alkanes unreactive?

A

Strong, non-polar covalent bonds.

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6
Q

How does the boiling point and melting point of alkanes change with carbon chain length?

A

Increases with carbon chain length.

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7
Q

What factors increase Tm/Tb in alkanes?

A

Stronger induced dipole intermolecular forces.

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8
Q

How does branching affect the melting point and boiling point of alkanes?

A

Generally lowers Tm/TB

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9
Q

Why does branching lower Tm/TB in alkanes?

A

Molecules have a lower surface area, resulting in weaker intermolecular forces.

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10
Q

What are the two states of particle motion in substances above absolute zero?

A

Vibrating about a fixed position (solid) or moving around (liquid or gas)

Particles possess kinetic energy in both states.

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11
Q

How is temperature (T) related to mean kinetic energy (KE) of particles?

A

Temperature is directly proportional to mean kinetic energy

Higher temperature indicates higher mean kinetic energy.

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12
Q

What happens to particles between states 1 and 2?

A

Particles are vibrating and gaining kinetic energy, causing the temperature to rise

This indicates an increase in energy.

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13
Q

What occurs between states 2 and 3 in a substance?

A

All energy goes into breaking intermolecular attractions, with no increase in kinetic energy or temperature

This phase is characterized by a constant temperature during the state change.

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14
Q

What happens between states 3 and 4?

A

Particles are moving around and gaining kinetic energy

This indicates an increase in energy as the substance heats up.

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15
Q

What characterizes the transition between states 4 and 5?

A

The substance is boiling, breaking intermolecular attractions without an increase in kinetic energy or temperature

This phase maintains a constant temperature during boiling.

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16
Q

What occurs between states 5 and 6?

A

Particles are moving rapidly and increasing in kinetic energy

This indicates a further increase in energy.

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17
Q

What happens at absolute zero?

A

Particles do not vibrate, resulting in no kinetic energy

Absolute zero is the theoretical point at which all molecular motion stops.

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18
Q

What is latent heat?

A

The energy required to change state without any change in temperature

It is crucial during phase transitions.

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19
Q

What happens during condensation and solidifying?

A

Energy is released as heat energy, preventing further temperature decrease

Mean kinetic energy of particles remains constant during these processes.

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20
Q

Why do liquids cool as they evaporate?

A

Some kinetic energy is used to overcome forces between particles, lowering the mean kinetic energy of remaining particles

This results in a decrease in temperature.

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21
Q

What are the main components formed from the decay of marine animals and plants over millions of years?

A

Crude oil and natural gas

Formed under heat and pressure in the absence of air.

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22
Q

What is required for crude oil to be useful?

A

Its components must be partly separated and possibly modified

This process uses differences in physical properties of alkanes.

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23
Q

What method is used to separate the compounds in crude oil?

A

Fractional distillation

This method is performed at an oil refinery.

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24
Q

How does the boiling point of alkanes change with chain length?

A

It increases with longer alkane chains

Due to greater van der Waals’ forces.

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25
What type of forces exist between molecules of alkanes?
Van der Waals' forces C-H bonds are virtually non-polar.
26
True or False: A branched chain alkane has a higher boiling point than a straight chain alkane of the same formula.
False A branched chain alkane has a lower boiling point than the straight chain alkane.
27
Fill in the blank: The more branching in an alkane chain, the ______ the boiling point.
lower Less branching allows closer contact between molecules and stronger van der Waals' forces.
28
As the C chain gets longer the hydrocarbons:
1. Become more viscous 2.harder to ignite 3. Less volatile 4 having higher bp
29
How does the size of the hydrocarbon link to its bp and why?
As the alkane chain gets longer the melting and boiling points increase due to greater van der waal forces
30
What is a temperature gradient?
The higher up the column, the Cooler it will get; hot vapour will rise and condense relating to its bp
31
Describe fractional distillation.
1. Crude oil is vaporised 2. Vapour passed into a tower which is hot at top and cold at bottom 3. As the vapour rises it cools 4. Molecules will condense at different height in the tower and will have different boiling points 5. The longer the molecule (higher bp) It will confesses and cook lower down the column
32
What is cracking?
Cracking is when long chain hydrocarbons are broken into smaller molecules or compounds.
33
What is always a product of cracking?
An alkene.
34
What type of hydrocarbons are alkenes?
Unsaturated hydrocarbons.
35
Why are small chain molecules more valuable in industry?
They are more useful to industry and have a higher demand.
36
Which petroleum fractions are in more demand?
The fractions with shorter C chains (e.g. petrol and naphtha).
37
What is done to supply the demand for shorter hydrocarbons?
Longer hydrocarbons are cracked.
38
Are the products of cracking more or less valuable than the starting materials?
More valuable.
39
What is ethene used to make?
Poly (ethene).
40
What type of alkanes are produced by catalytic cracking?
Smaller, branched chain alkanes.
41
Fill in the blank: Cracking allows oil companies to turn less useful hydrocarbons into more useful ones like _______.
[plastics, polymers, and other higher demand fuels]
42
What is catalytic cracking?
A process using zeolite catalysts, heated to about 450°C and slightly above atmospheric pressure
43
What type of catalysts are used in catalytic cracking?
Zeolite catalysts (a form of aluminosilicate)
44
What is a key characteristic of zeolites?
They have microscopic pores and channels, resulting in a very high surface area
45
What types of hydrocarbons are produced by catalytic cracking?
* Branched hydrocarbons * Cyclic hydrocarbons (e.g., cyclohexane) * Aromatic hydrocarbons (e.g., benzene)
46
What does the circle in the benzene formula represent?
Delocalized electrons
47
What is thermal cracking?
A process that uses very high temperatures and high pressures to crack hydrocarbon molecules
48
What types of products are primarily produced by thermal cracking?
* Alkenes * Straight chain alkanes
49
Why is thermal cracking useful?
It is useful when producing polymers and other chemicals
50
What is the function of catalytic converters?
To remove CO, NOx, and unburned hydrocarbons from exhaust gases, converting them into CO2, N2, and H2O ## Footnote Catalytic converters use a ceramic honeycomb coated with a thin layer of catalyst metals such as Pt, Pd, and Rh.
51
What chemical reaction represents the conversion of carbon monoxide and nitrogen oxide in catalytic converters?
2CO + 2NO → 2CO2 + N2 ## Footnote This reaction illustrates the reduction of harmful emissions.
52
What is flue gas desulfurization?
A process to remove sulfur dioxide (SO2) from exhaust gases after burning fuel ## Footnote It is essential to prevent acid rain and respiratory problems.
53
What happens to sulfur during the combustion of fuels?
Sulfur dioxide (SO2) is formed ## Footnote This acidic oxide can react with water to create acid rain.
54
What is the reaction that forms acid rain from sulfur dioxide?
SO2 + H2O → H2SO4 ## Footnote This reaction leads to the formation of sulfuric acid, a component of acid rain.
55
How is sulfur typically removed from fuels?
Before burning or by flue gas desulfurization after burning ## Footnote This helps mitigate the environmental impact of sulfur emissions.
56
What materials are often used in the scrubbing process during flue gas desulfurization?
Calcium oxide (CaO) or calcium carbonate (CaCO3) ## Footnote These materials react with sulfur dioxide to form gypsum.
57
What is the chemical reaction for the formation of gypsum from calcium oxide and sulfur dioxide?
CaO + SO2 → CaSO3 ## Footnote This is an acid-base reaction that produces calcium sulfite, which can further react to form gypsum.
58
What is gypsum?
A product formed from the reaction of sulfur dioxide with calcium compounds ## Footnote It is commonly used in construction and agriculture.
59
60
What is the greenhouse effect?
A natural process that occurs when gases in the Earth's atmosphere trap heat from the sun, warming the planet. ## Footnote The greenhouse effect is essential for maintaining the Earth's temperature suitable for life.
61
How does the greenhouse effect work?
Gases in the atmosphere absorb the sun's heat, trapping it and preventing it from escaping into space. ## Footnote This process is crucial for regulating Earth's climate.
62
Why is the greenhouse effect important?
It keeps the Earth's temperature at a level that supports life. ## Footnote Without the greenhouse effect, Earth would be too cold for most life forms.
63
What is causing the increase in the greenhouse effect?
Human activities are increasing the concentration of greenhouse gases in the atmosphere. ## Footnote Examples include burning fossil fuels, deforestation, and industrial processes.
64
What is the primary driver of climate change?
The greenhouse effect. ## Footnote It contributes to rising average temperatures and more extreme weather events.
65
What are some consequences of climate change?
Rising average temperatures, more extreme weather events, and other consequences. ## Footnote These effects can lead to significant environmental, social, and economic impacts.
66
What is the ozone layer
- allottope of oxygen -it is a very high area of the atmosphere rich in ozone - it absorbs UV light radiation from sun and prevents it from reaching the surface of earth.
67
What is the process of ozone formation?
Ozone is formed by ultraviolet light reacting with oxygen molecules to create oxygen free radicals, which then react with molecular oxygen to form ozone. ## Footnote The overall reaction can be summarized as: UV + 3O2 → 2O3.
68
What is the chemical equation for the formation of oxygen free radicals?
O2 → •O• + •O• ## Footnote Oxygen free radicals are highly reactive species that play a crucial role in ozone formation.
69
What happens when an ozone molecule absorbs ultraviolet light?
It dissociates to form an oxygen molecule and an oxygen atom: O3 → •O• + O2 ## Footnote This process contributes to ozone depletion.
70
Is the natural formation and degradation of ozone by UV radiation a reversible reaction?
Yes, it is a reversible reaction: O3 = •O• + O2 ## Footnote This means that ozone can be formed and broken down under natural conditions.
71
What is the overall reaction for ozone depletion?
2O3 = 3O2 ## Footnote This represents the loss of ozone in the atmosphere due to its breakdown.
72
What are chlorofluorocarbons (CFCs)?
Halogenoalkane molecules ## Footnote CFCs contain chlorine and fluorine atoms replacing some hydrogens in alkanes.
73
What role do CFCs play in refrigeration?
Useful refrigerants or inert molecules ## Footnote CFCs are commonly used due to their stability and effectiveness.
74
What effect does UV light have on CFCs?
Breaks C-Cl bonds to form chlorine free radicals ## Footnote The reaction is represented as: CCI3CCl2F → • CCICCIF + •Cl.
75
Which bond in CFCs is too strong to be broken by UV light?
C - F bond ## Footnote This stability contributes to the persistence of CFCs in the atmosphere.
76
What is the reaction between chlorine radicals and ozone?
• Cl + O3 → ClO• + O2 ## Footnote This reaction leads to the decomposition of ozone.
77
What happens when chlorine oxide radicals react with ozone?
ClO• + O3 → O2 + • Cl ## Footnote This reaction further decomposes ozone and regenerates chlorine radicals.
78

Chemistry A-level - Mr Donelly (4 decks)

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