Alkanes Flashcards
Identify a compound that is used to react with the sulfur dioxide in the products of combustion before they enter the atmosphere.
Give one reason why this compound reacts with sulfur dioxide.
- Calcium oxide / calcium carbonate
Allow any base or alkali
Allow correct formulae - Neutralises the SO2 / acid base reaction / it is a base
Ethanethiol (C2H5SH) and ethanol molecules have similar shapes.
Explain why ethanol has the higher boiling point.
Ethanol contains hydrogen bonding
Breaking covalent bonds which is stronger than IMF (VDW / dipole-dipole forces) in ethanethiol /
(H bonding) is the strongest IMF
Describe and explain the use of alkanes as fuels as well as the trend in this with increasing carbon chain length
Alkanes, when catalysed by heat or a spark, make excellent fuels that react with oxygen in an exothermic reaction known as a combustion reaction. The greater the number of carbon atoms, the greater the energy produced, but also the more oxygen required.
Summarise the physical properties of alkanes
- Insoluble in water
- Soluble in organic compounds
- Low melting and boiling points
Summarise the chemical properties of alkanes
- Non-polar bonds
- Van der Waals intermolecular bonds
- Very unreactive
- Undergoes combustion and reactions with halogens
Describe and explain how a Fractionating Column works
It is hotter near the base of the column but much cooler near the top. When the crude oil is passed into the tower, near the bottom, most of the mixture boils and starts to rise up the tower. As the mixture rises up the tower, it starts to cool down and will gradually condense back into liquid form at different temperatures. The liquid mixture will be collected at different condensation points. The larger hydrocarbons, with higher boiling points, condense first and are collected near the base of the column. The smaller hydrocarbons, with lower boiling points, condense later and higher up the column; they are decanted near the top of the column. Petroleum gases like methane and ethane go all the way up to the top of the column and are collected there. Note that the process involves breaking intermolecular forces only; the molecules themselves are unaffected by this process. This process does not actually separate the crude oil mixture into pure hydrocarbon components, but into mixtures called fractions. Fractions are mixtures of hydrocarbons with similar boiling points and carbon chain lengths. In many cases, these fractions can be used directly, but sometimes further separation is required to access purer components.
State the order of fractions from the top of the column to the bottom
- Refinery Gas
- Gasoline
- Naphtha
- Kerosene/Paraffin
- Diesel Oil/Gas Oil
- Fuel Oil
- Lubricating Oil
- Residue
What’s crude oil?
Mixture of fractions (hydrocarbons with similar boiling points and properties) formed at high temperatures and pressures deep below earth’s surface over millions of years (therefore non-renewable)
What are the conditions for thermal cracking?
- High temperature (400 – 1000^C)
- High pressure (70 atm)
What’s usually used as the starting material in thermal cracking?
Naphtha (C7 - C14)
What are the conditions for catalytic cracking?
- High temperature (450^C, which is generally lower than in thermal cracking)
- Slight pressure (slightly greater than 1 atm)
- Zeolite catalyst present
What are the favoured products in catalytic cracking and what are they used for?
Branched alkanes & cycloalkanes, which are widely used in motor fuels and benzene which has a variety of uses
Which of the 2 types of cracking is cheaper and more efficient? Why?
Catalytic cracking as it uses a lower temperature and pressure
Explain the most important product of catalytic cracking
The most important product of catalytic cracking is 2-methylheptane, which is the major component of petrol
What are liquified petroleum gases used for?
Camping gas & cooking gas
What is petrol used for?
Fuel for cars, motorbikes & machines
What is kerosene used for?
Fuel for planes, lamps & ovens
What is diesel used for?
Fuel for lorries & central heating systems
What is fuel oil used for?
Fuel for ships & power stations
What is wax used for?
Fuel for candles
Is the combustion of alkanes exo or endothermic? Why does this matter?
Exothermic, which means that heat energy is released. This heat energy can be used for direct heating (e.g. camping gas, central heating, candles). It can also be converted into mechanical energy (e.g. cars, lorries, ships), or even electrical energy (e.g. power stations).
Give an example of when incomplete combustion is desirable
Occasionally incomplete combustion is desirable – such as with a Bunsen burner. Closing the air hole produces a yellow flame (the yellow colour results from hot carbon particles) and this makes the flame more visible and causes a more gentle heat.
Give the equations of the reactions that occur when air is exposed to high temperatures and/or sparks. When does this happen IRL?
- N2 (g) + O2 (g) -> 2NO (g)
- 2NO (g) + O2 (g) -> 2NO2 (g)
- This usually occurs near or in internal combustion engines where there’s very high temperature & pressure and a spark.
Why is the production of NOx in combustion of alkanes associated with pollution problems?
- Nitrogen dioxide (NO2) dissolves in rainwater to form an acidic solution and contributes to the problem of acid rain
- Nitrogen oxides can also combine with unburned hydrocarbons to produce photochemical smog or a brown haze, which is caused when UV light reacts with the nitrogen oxide pollutants.
Why is the production of unburned hydrocarbons in combustion of alkanes associated with pollution problems?
- They:
1. are toxic and can cause cancer if breathed in
2. combine with oxides of nitrogen to produce photochemical smog.
What are the 2 ways (in spec) to reduce the polluting effects associated with the burning of fossil fuels?
- Flue gas desulphurisation
- Catalytic Converters
Briefly explain Flue Gas Desulphurisation. Include equations if necessary
Many factory chimneys contain alkaline materials such as lime (calcium oxide). These absorb the acidic gases such as SO2 and thus prevent them from escaping:
SO2 (g) + CaO (s) -> CaSO3 (s)
Further reactions result in the formation of CaSO4 (gypsum) which is used to make plaster
Briefly explain Catalytic Converters. Include equations if necessary
Most modern car exhausts are now fitted with catalytic converters. These are designed to convert some of the more harmful gases present in car exhausts into less harmful ones. Unburned hydrocarbons, carbon monoxide and the oxides of nitrogen can all be converted into less harmful gases inside these converters. The catalysts used are platinum, palladium and rhodium. There are two main types of reaction taking place in a catalytic converter:
- The removal of carbon monoxide and nitrogen monoxide -
2NO (g) + 2CO (g) -> N2 (g) + 2CO2 (g)
where harmful NO and CO gases are converted into the less harmful nitrogen and carbon dioxide - The removal of unburned hydrocarbons and nitrogen monoxide, for example -
C8H18 + 25NO -> 8CO2 + 9H2O + 12.5N2
where harmful unburned hydrocarbons and oxides of nitrogen are converted into the less harmful carbon dioxide, water and nitrogen
Why is the production of SO2 from combustion of alkanes a pollution problem? Give equations if necessary
Because:
H2O + SO2 -> H2SO2
The product is known as sulphurous acid which occurs in clouds and causes acid rain. This causes various problems, including the erosion of buildings and statues, damage to plants and trees and the killing of fish and other wildlife, through the contamination of lakes.
Why is Carbon produced from incomplete combustion of alkanes a problem?
Causes cancer, asthma and global dimming
Explain how photochemical smog is formed and why it’s bad for you
Ozone can cause photochemical smog at lower levels. Ozone occurs in the lowest level of the atmosphere, existing as a mixture sunlight, hydrocarbons and NO2. A great deal of hydrocarbons and NO2 come from cars and factories. When solid carbon particulates and ozone mix we create photochemical smog. This harms the respiratory system in animals and damages plants. Ozone itself is also toxic to humans.
Write an equation for the reaction between nitrogen and oxygen to form nitrogen monoxide
N2 + O2 -> 2NO
State the order of fractions in a fractionating column from the top of the column to the bottom
- Refinery Gas
- Gasoline
- Naphtha
- Kerosene/Paraffin
- Diesel Oil/Gas Oil
- Fuel Oil
- Lubricating Oil
- Residue
State refinery gas’ range of carbon chain length, its use and the temperature at which it condenses
C1-C4, used as fuel, doesn’t condense
Which crude oil fraction has a C1-C4 chain length, is used as fuel and doesn’t condense
Refinery Gas
State gasoline’s range of carbon chain length, its use and the temperature at which it condenses
C5-C12, used as fuel in cars (petrol), 30°C
Which crude oil fraction has a C5-C12 chain length, is used as fuel in cars and condensers at 30°C
Gasoline
State naphtha’s range of carbon chain length, its use and the temperature at which it condenses
C7-C14, used to make chemicals, 110°C
Which crude oil fraction has a C7-C14 chain length, is used to make chemicals and condenses at 110°C
Naphtha
State kerosene/paraffin’s range of carbon chain length, its use and the temperature at which it condenses
C11-C15, used as a fuel in het engines & oil stoves, 180°C
Which crude oil fraction has a C11-C15 chain length, is used as a fuel in jet engines & oil stoves and condenses at 180°C
Kerosene/Paraffin
State diesel oil/gas oil’s range of carbon chain length, its use and the temperature at which it condenses
C15-C19, used as a fuel in diesel engines, 260°C
Which crude oil fraction has a C15-C19 chain length, is used as a fuel in diesel engines and condenses at 260°C
Diesel Oil/Gas Oil
State fuel oil’s range of carbon chain length and its use
C20-C30, used as a fuel for ships & home heating systems
Which crude oil fraction has a C20-C30 chain length and is used as a fuel for ships & home heating systems
Fuel Oil
State lubricating oil’s range of carbon chain length
C30-C50
Which crude oil fraction has a C30-C50 chain length
Lubricating Oil
State residue’s range of carbon chain length, use and temperature at which it condenses
> C50, used to make bitumen for roofing and surfacing roads, 340°C
Which crude oil fraction has a >C50 chain length, is used to make bitumen for roofing and surfacing roads and condenses at 340°C?
Residue
State why it is desirable to decrease emissions of oxides of nitrogen from vehicles
Formation of acid rain / causes respiratory problems
