Alkanes as Fuels
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what is the equation for complete combustion
hydrocarbon + oxygen = carbon dioxide + water
what would the complete combustion of propane look like
• propane has a molecular formula of C3H8 • so the combustion equation is C3H8 + ?02 = ?CO2 + ?H20 • there are three carbons on the left so there are 3 CO2 molecules • there are 8 hydrogens so there are 4 H20 molecules • on the right that makes a total of 10 oxygen atoms • so on the left there must be 5 02 molecules • giving: C3H8 + 5O2 = 3CO2 + 4H20
what is the first problem or disadvantage that comes to mind when completely combusting a hydrocarbon
• CO2 is produced as a byproduct • which contributes to the greenhouse effect • which accelerates global warming and climate change
what is incomplete combustion
when all of the hydrocarbon doesnt completely burn with oxygen
why would incomplete combustion take place
• if there was an insufficient supply of oxygen present during the burning • or the reaction was too rapid
what happens to the hydrogen atoms during incomplete combustion and is the product harmful
• they burn with oxygen and just form water - this is a harmless product
what happens to the carbon atoms during incomplete combustion
• some of the carbon atoms form gaseous carbon monoxide • or solid carbon • these are harmful products and can cause issues
why can you know when solid carbon has been formed in incomplete combustion just from looking
• as the solid carbon can be seen as smoke in the air - or soot on the burner
what would be the equation for the incomplete combustion of propane that forms two moles of CO2 as one of the products, with solid carbon being the polluting byproduct
• C3H8 + ?O2 = 2CO2 + ?C + ?H20 • you have 8 hydrogens on the left so 4 H20 on the right • you then have a total of 8 oxygens on the right so you have 4 O2 on the left • and you have 2 carbons on the right when there are 3 on the left so you only have one carbon atom forming the solid • C3H8 + 4O2 = 2CO2 + C + 4H20
how would you explain the combustion of the propane that took place in the previous equation
• 2 out of 3 of propane’s carbon atoms completely combusted - while the last one doesnt
what does the solid carbon actually look like
• tiny particles in the atmosphere - which can be breathed in or influence climate change
what does carbon monoxide do when breathed in
• it prevents the transport of oxygen around the body - as it binds to haemoglobin in the red blood cells more strongly than oxygen does
why is carbon monoxide such a dangerous gas
• it is colourless and odourless • so people breathe it in without knowing • hence why its called the silent killer
what would the equation be for the incomplete combustion of propane if one mole of CO2 was produced on the right side, with carbon monoxide being one of the byproducts
• C3H8 + ?O2 = CO2 + ?CO + ?H20 • 8 hydrogens so 4 H20s • 3 carbons on the left so you have 2 COs • meaning you have a total of 8 oxygens on the right • so you have 4 O2s • C3H8 + 4O2 = CO2 + 2CO + 4H20
what are unburned hydrocarbons
• hydrocarbons that dont burn at all during combustion - abbreviated to HC
what happens to unburnt hydrocarbons since they dont burn
they are released into the atmosphere unchanged
why should atoms of sulfur in molecules in crude oil not theoretically be there when burning a hydrocarbon
• because they can be removed by fractional distillation, cracking and reforming • but neither of these are perfect
what products are formed when a hydrocarbon with sulfur impurities is burned and then released into the atmosphere
• when burned sulfur dioxide is formed and released - when in the atmosphere it can react with it to form sulfur trioxide
what are the equations for the production of sulfur dioxide and trioxide
• S + O2 = SO2 - 2SO2 + O2 = 2SO3
what kind of gases are sulfur dioxide and trioxide and what do they from when dissolved in water
• they are both acidic oxides • when dissolved in water sulfur dioxide forms sulfurous acid • and sulfur trioxide forms sulfuric acid
what is the equation for the production of sulfurous acid and sulfuric acid
• SO2 + H20 = H2SO3 (sulfurous acid) - SO3 + H20 = H2SO4 (sulfuric acid)
what do both of these form in the atmosphere and what are its impacts
• they form acid rain • which causes environmental damage • to things like aquatic life and crops
how are oxides of nitrogen formed
• under very high temperatures like in car engines • nitrogen molecules can burn with oxygen molecules in the air • to form various oxides of nitrogen
what is the formula for an oxide of nitrogen and what are the most common ones
• NOx • the common ones are nitrogen monoxide (NO) • and nitrogen dioxide (NO2)