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Chemistry > 3.2 - Alkanes > Flashcards

3.2 - Alkanes Flashcards

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1
Q

What is an alkane?

A

A saturated hydrocarbon containing C-H bonds only.

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2
Q

What is the general formula of an alkane?

A

CnH2n+2

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3
Q

Does a hydrocarbon have polar or nonpolar bonds? Why/why not?

A

Nonpolar - carbon and hydrogen have similar electronegativities.

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4
Q

What intermolecular forces does a hydrocarbon contain and why?

A

Only Van der Waals forces of attraction - bonds are non-polar.

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5
Q

Are hydrocarbons soluble in water? Why?

A

They are insoluble because hydrogen bonds in water are stronger than alkanes’s van der waals forces of attraction.

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6
Q

How reactive are alkanes

A

Very unreactive

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7
Q

Which reactions will alkanes undergo?

A

Combustion and reaction with halogens.

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8
Q

What is crude oil? How is it formed? Is it renewable?

A

Mixture of fractions (hydrocarbons with similar BP and properties).
Formed at high temperatures and pressures deep below earth’s surface over millions of years -> therefore non-renewable.

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9
Q

What is fractional distillation and how does it work?

A
  1. Crude oil heated until mostly vapourised.
  2. Passed into a fractionating tower that is cooler at the top than the bottom.
  3. Liquid fractions are piped off at the bottom.
  4. Vapours rise up the column and - via trays and bubble caos - condense when temperature id below their boiling point.
  5. Shortest chain hydrocarbons condense at the top as they have the lowest BPs.
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10
Q

What is frackiing and how is it done?

A
  • Natural gas is held within shale rock.
  • Drill into shale, force pressurised water and sand into rock to fracture it, collect gas.
  • HCl and methanol added to break up shale prevent corrosion.
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11
Q

Pros and cons of fracking?

A

Pros:
- Gas supply for many years.
- Reduces imported gas and electricity.
Cons:
- Lots of traffic to local area.
- Concern about the amount of water useed.
- Chemical additives can polute water supplies.
- Can cause earthquakes.
- Combust CH4 –>CO2 which leads to global warming.

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12
Q

Why are alkanes cracked?

A

To turn long chain alkane (not economically valuable) into a shorter chain alkane (more economically valuable becaus eit can be used as fuel) and an alkene(more reactive, starting point for many products).

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13
Q

What are the conditions for thermal cracking?

A
  • 700-1200K temperature
  • Up to 7000kPa pressure
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14
Q

What is the intermediate for the reaction?

A

Free radicals

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15
Q

What are the main products of thermal cracking?

A

Alkenes

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16
Q

What are the conditions of catalytic cracking?

A
  • Lower temp (720K)
  • Lower pressure (but above atmospheric)
  • Zeolite catalyst (SiO2 and Al2O3) with a honecomb structure to give a large surface area.
17
Q

What are the main products of catalytic cracking?

A

Cycloalkanes, aromatic hydrocarbons, branched alkanes.

18
Q

Write an equation for the combustion of propane.

A

C3H8 + 5O2 –> 3CO2 + 4H2O

19
Q

What is a fuel?

A

Something which releases heat energy when combusted.

20
Q

What are the five main fuels comprising of alkanes?

A

Methane, butane, prpane, pertrol, paraffin.

21
Q

What is incomplete combustion and what products are formed in the case of alkanes?

A

Combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming

22
Q

Which type of hydrocarbons are most likely to undergo incomplete combustion?

A

The ones with longer chains.

23
Q

Whar is the environmental impact of carbon monoxide?

A

It is toxic/poisonous.

24
Q

What is the environmental impact of nitrogen oxides?

A

Form nitric acid -> acid rain, photochemical smog

25
Q

What is the environmental impact of sulfur impurities/sulfur dioxide?

A

Form sulphuric acid -> acid rain

26
Q

What is the environmental impact of soot (carbon)?

A
  • Asthma
  • Cancer
  • Global dimming
27
Q

What is the environmental impact of unburnt hydrocarbons?

A

Photochemical smog

28
Q

What is the environmental impact of Carbon Dioxide?

A

Greenhouse gas = global warming, increases global temperature, speeds up climate change.

29
Q

What is the environmental impact of water vapour?

A

Greenhouse gs -> global warming, increases global temperatures, speeds up climate change.

Chemistry (35 decks)

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