12.4- COMBUSTION OF ALKANES Flashcards
How reactive are alkanes?
quite unreactive
What do alkanes not react with?
acids, bases, oxidising agents or reducing agents
What do alkanes burn and react with under suitable conditions?
burn and will react with halogens under suitable conditions
How well do shorter chain alkanes burn in a plentiful supply of oxygen?
burn completely
What is produced when shorter chain alkanes are burnt in a plentiful supply of oxygen?
carbon dioxide and water
What does combustion reactions give out?
give out heat
What is the enthalpies of combustion like?
large negative enthalpies
What is greater when there’s more carbon present in combustion?
greater the heat output
Why are alkanes with more carbon important in fuels?
when combusted they have a great heat output
What are fuels?
substances that release heat energy when they undergo combustion
What do fuels store a large amount of in a small amount of weight?
store a large amount of energy for a small amount of weight
Examples of alkane fuels? (5)
methane propane butane petrol paraffin
What fuel is methane used for?
natural or North Sea gas
What fuel is propane used for?
camping gas
What fuel is butane used for?
calor gas
What types of hydrocarbons make up petrol?
mixture of hydrocarbons of approximate chain length C8
What does a limited supply of oxygen in combustion cause the production of?
poisonous gas carbon monoxide
What sort of combustion is it when carbon monoxide is formed?
incomplete combustion
What is produced when even less oxygen is provided in combustion?
carbon (soot)
Example of carbon (soot) being formed from incomplete combustion in lab?
when Bunsen burner used with a closed air hole, flame is yellow and black sooty deposit appears on apparatus
When does incomplete combustion often happen?
often happens when with longer chain hydrocarbons
Why does incomplete combustion often happen with longer chain hydrocarbons?
they need more oxygen to burn compared with shorter chains
What do all hydrocarbon-based fuels derived from crude oil may produce when they’re burnt?
polluting products
Different types of polluting products made from when hydrocarbon-based fuels derived from crude oil are burnt? (7)
carbon monoxide nitrogen oxides sulfur dioxide carbon particles unburnt hydrocarbons carbon dioxide water vapour
What is carbon monoxide?
poisonous gas produced by incomplete combustion
Examples of nitrogen oxides?
NO, NO2, N2O4
How are nitrogen oxides formed?
produced when there is enough energy for nitrogen and oxygen in the air to combine
Equation of how nitrogen and oxygen combine to form nitrogen oxides?
N2 (g) + O2 (g) = 2NO (g)
Example of where does nitrogen and oxygen combine to form nitrogen oxides?
petrol engine at high temperatures present, when sparks ignite fuel
What may the nitrogen oxides from petrol engine react with to form?
oxides may react with ester vapour and oxygen in the air to form nitric acid
As the nitrogen oxides from petrol engines eventually produce nitric acid, what are they contributors of?
contributors of acid rain and photochemical smog
What is sulphur dioxide a contributor of?
acid rain
Where is sulphur dioxide produced from?
produced from sulphur-containing impurities present in crude oil
How does sulphur dioxide produce acid rain?
this oxide combines with water vapour and oxygen in the air to form sulphuric acid
What are carbon particles called?
particulates
What can particulates exacerbate and cause?
exacerbate asthma and cause cancer
What type of gas is carbon dioxide?
greenhouse gas
What is always produced when hydrocarbons are burnt?
carbon dioxide
What is the increasing levels of carbon dioxide in the atmosphere causing?
cause of an increase in the Earth’s temperature and consequent climate change
What type of gas is water vapour?
greenhouse gas
How do a large number of power stations generate electricity?
by burning fossil fuels such as coals or natural gas
What do coals and natural gas contain?
sulphur compounds
What is a product of combustion of coals and natural gases as they contain sulphur compounds?
sulphur dioxide, SO2
What does sulphur dioxide cause?
acid rain
How does sulphur dioxide cause acid rain?
by combining with oxygen and water in the atmosphere to form sulphuric acid
Equation for how sulphur dioxide reacts with oxygen and water to form sulphuric acid?
S02 (g) + 1/2O2 (g) + H20 (l) = H2SO4 (l)
What is the gases given out by power stations called?
flue gas
What is the process of removing the sulphur dioxide from flue gas called?
flue gas desulphurisation
What is one method of flue gas desulphurisation?
slurry of calcium oxide (lime) + water is sprayed into the flue gas which reacts with calcium oxide + water to form calcium sulphite, which can be further oxidised to calcium sulphate
What is calcium sulphate also called?
gypsum
What is the overall reaction of flue gas desulphurisation into gypsum?
CaO (s) + 2H20 (l) + S02 (g) + 1/2O2 = CaSO4.2H20(s)
What is gypsum used to make?
builder’ plaster and plasterboard
What is an alternative method of flue gas desulphurisation?
use calcium carbonate (limestone) rather than calcium oxide
What is the equation for flue gas desulphurisation using calcium carbonate?
CaCO3 (s) + 1/2O2 (g) + SO2 (g) = CaSO4 (s) + CO2 (g)
What does the internal combustion produce most of?
most of the pollutants listed previously
What is removed from petrol to make it less of a problem?
sulphur removed from petrol so sulphur dioxide has become less of a problem
What are all new cars with petrol engines now equipped with?
catalytic converters in their exhaust systems
What do the catalytic converters in the exhaust systems of petrol engine cars do?
reduce output of carbon monoxide, nitrogen oxides and unburnt hydrocarbons in the exhaust gas mixture
What is the catalytic converter?
honeycomb made of a ceramic material coated with platinum and rhodium metals
What are the catalysts on a catalytic converters?
platinum and rhodium
What does the honeycomb structure of catalytic converters provide?
provide enormous surface area, so little of these expensive metals (platinum + rhodium) go a long way
What happens when the polluting gases pass over the catalyst of the catalytic converter?
react with each other to form less harmful products
Equation for how carbon monoxide reacts with nitrogen oxide over catalytic converter?
2CO (g) + 2NO (g) = N2 (g) + 2CO2 (g)
Word equation for how hydrocarbons react with nitrogen oxide over catalytic converter?
hydrocarbons + nitrogen oxide = nitrogen + carbon dioxide + water
Where does the reactions take place on the catalytic converter?
on the surface of the catalyst, on the layer of platinum and rhodium metals
What is the temperature like inside a greenhouse?
greenhouses become very warm inside
Why does it become very warm inside a greenhouse?
because visible rays from sun pass through the glass
What happens to the visible rays that pass through the glass of a greenhouse?
rather than escaping, their energy is absorbed by everything inside the greenhouse and re-radiated as infrared energy (heat)
What is the wavelength of infrared energy in comparison to visible rays?
infrared energy has a longer wavelength
Can infrared energy pass out of the glass of greenhouses?
no
How does carbon dioxide behave in terms of a greenhouse?
like glass
How does carbon dioxide act like glass of a greenhouse?
it traps infrared radiation so that the Earth’s atmosphere heats up
Why is carbon dioxide and other greenhouse gases important?
without it the Earth would be too cold to sustain life
What are examples of other greenhouse gases other than carbon dioxide? (2)
water vapour and methane
Are methane and water vapour more effective than carbon dioxide?
yes
How has the levels of methane and water vapour in the atmosphere changed over the years?
not been much change
What has happened since the industrial revolution?
fossil fuels have been used to fuel industrial plants and the level of carbon dioxide has been rising
As the levels of CO2 has been rising, what has also been increasing?
Earth’s temperature
What is the most abundant greenhouse gas?
water vapour
How does the concentration of water vapour change in the atmosphere?
tends to stay the same
Where does the concentration of water vapour in the atmosphere not stay the same?
near waterfalls
Why does the concentration of water vapour in the atmosphere tend to stay the same?
because of the equilibrium that exists between water vapour and liquid water
What happens to water vapour when there’s an increase in temperature?
will be more water vapour in the air and so more greenhouse warming
What can the increase in water vapour in the air be offset by?
offset by greater cloud formation and clouds reflect solar radiation
Why are many people concerned about activities such as airline flights?
they produce large amounts of carbon dioxide
What are activities that produce no carbon dioxide emission overall refereed to as?
carbon neutral
