combustion Flashcards
describe combustion
combustion reacts give out heat and have large negative enthalpies
what happens when there is more carbon present during a combustion reaction
the more carbons present, the greater the heat output
define a fuel
substances that release heat energy when they undergo combustion
they also store a large amount of energy for a small amount of weight
define incomplete combustion
when fuels are burnt in a limited supply of oxygen, the poisonous gas carbon monoxide, CO is formed
when is incomplete combustion most common
incomplete combustion often happens with long chain hydrocarbons which need more oxygen to burn compared with shorter chains
state all pollution products that may occur when hydrogen-carbon based fuels burn
carbon monoxide
nitrogen oxides
sulfur dioxide
particulates
sulfur dioxide
unburnt hydrocarbons
carbon dioxide
water vapour
how is carbon monoxide made
by incomplete combustion
how are nitrogen oxides produced
when there is enough energy for nitrogen and oxygen in the air to combine
For example, this happens in a petrol engine at high temperatures present. these oxides may react with water vapor and oxygen in the air to form nitric acid. they are therefore contributors to acid rain and photochemical smog
what are the three type of nitrogen oxide
NO
NO2
N2O4
THEY ARE OFTEN ABBREVIATED TO NOX
How is sulfur dioxide made
it is produced from sulfur-containing impurities present in crude oil. this oxide combines with water vapour and oxygen in the air to form sulfuric acid
sulfur dioxide is a contributor to acid rain
what can carbon particulates do
exacerbate asthma and cause cancer
what do unburnt hydrocarbons do
unburnt hydrocarbons may enter the atmosphere and these are significant greenhouse gases
they contribute to photochemical smog which can cause a variety of health problems
what does sulfur dioxide do
a gas that causes acid rain by combining oxygen and water in the atmosphere to form sulfuric acid
what are the gases given out by power stations called
flue gases
what is the process of removing sulfur dioxide called
flue gas desulfirisation
explain the method of flue gas desulfirisation
a slurry of calcium oxide and water is sprayed into the flue gas which reacts with the calcium oxide and water to form calcium sulfite, which can be further oxidized to calcium sulfate this is also called gypsum
define gypsum
gypsum is a saleable product as it is used to make builders’ plaster and plasterboard
what happens in the alternative process of flue gas desulfirisation
an alternative process uses calcuim carbonate rather than calcuim oxide
what produces the most of the pollutatnts
the internal combustion engine produces most of the pollutants, though sulfur is now removed from petrol so that sulfur dioxide has become less of a problem
what do all new cars have
all new cars with petrol engines are now equipped with catalytic converters in their exhaust systems.
these reduce the output of carbon monoxide, nitrogen oxides, and unburnt hydrocarbons in the exhaust gas mixture
what is the catalytic convertor made of
the catalytic convertor is a honeycomb made of ceramic material coated with platinum and rhodium metals
these are the catalysts.
what does the honeycomb shape provide for the catalytic convertor
an enormous surface area, so a little of expensive metals goes a long way
what happens with the polluting gases in the catalytic convertor
as the polluting gases pass over the catalyst, they react with each other to form less harmful products
the reactions take place on the surface of the catalyst, on the layer of platinum and rhodium metals
explain why greenhouse gases become very warm inside
green house gases become very warm inside.
visible rays from the sun pass through the glass
rather than escaping their energy is absorbed by everything inside the greenhouse and re-radiated as infrared energy, which is heat
infrared energy has a longer wavelength and cannot pass back out through the glass
why is carbon dioxide important
it traps infrared radiation so that the Earth’s atmosphere heats up
this is important for life because, without carbon dioxide and other greenhouse gases, the earth would be too cold to sustain life
why does the concentration of water vapour stay roughly the same
because of the equilibrium that exists between the water vapour and liquid water
what would happen if the temperature of the atmosphere rises
there will be more water vapour in the air and therefore more greenhouse warming.
this may be offset by greater cloud formation and clouds reflect solar radiation
define carbon-nuetral
activities that produce no cabron dioxide emissions overall are referred to as carbon neutral
