Alkanes as Fuels

Question 1

what is the equation for complete combustion

Answer 1

hydrocarbon + oxygen = carbon dioxide + water

Question 2

what would the complete combustion of propane look like

Answer 2

• 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

Question 3

what is the first problem or disadvantage that comes to mind when completely combusting a hydrocarbon

Answer 3

• CO2 is produced as a byproduct
• which contributes to the greenhouse effect
• which accelerates global warming and climate change

Question 4

what is incomplete combustion

Answer 4

when all of the hydrocarbon doesnt completely burn with oxygen

Question 5

why would incomplete combustion take place

Answer 5

• if there was an insufficient supply of oxygen present during the burning
• or the reaction was too rapid

Question 6

what happens to the hydrogen atoms during incomplete combustion and is the product harmful

Answer 6

• they burn with oxygen and just form water

- this is a harmless product

Question 7

what happens to the carbon atoms during incomplete combustion

Answer 7

• some of the carbon atoms form gaseous carbon monoxide
• or solid carbon
• these are harmful products and can cause issues

Question 8

why can you know when solid carbon has been formed in incomplete combustion just from looking

Answer 8

• as the solid carbon can be seen as smoke in the air

- or soot on the burner

Question 9

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

Answer 9

• 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

Question 10

how would you explain the combustion of the propane that took place in the previous equation

Answer 10

• 2 out of 3 of propane’s carbon atoms completely combusted

- while the last one doesnt

Question 11

what does the solid carbon actually look like

Answer 11

• tiny particles in the atmosphere

- which can be breathed in or influence climate change

Question 12

what does carbon monoxide do when breathed in

Answer 12

• it prevents the transport of oxygen around the body

- as it binds to haemoglobin in the red blood cells more strongly than oxygen does

Question 13

why is carbon monoxide such a dangerous gas

Answer 13

• it is colourless and odourless
• so people breathe it in without knowing
• hence why its called the silent killer

Question 14

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

Answer 14

• 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

Question 15

what are unburned hydrocarbons

Answer 15

• hydrocarbons that dont burn at all during combustion

- abbreviated to HC

Question 16

what happens to unburnt hydrocarbons since they dont burn

Answer 16

they are released into the atmosphere unchanged

Question 17

why should atoms of sulfur in molecules in crude oil not theoretically be there when burning a hydrocarbon

Answer 17

• because they can be removed by fractional distillation, cracking and reforming
• but neither of these are perfect

Question 18

what products are formed when a hydrocarbon with sulfur impurities is burned and then released into the atmosphere

Answer 18

• when burned sulfur dioxide is formed and released

- when in the atmosphere it can react with it to form sulfur trioxide

Question 19

what are the equations for the production of sulfur dioxide and trioxide

Answer 19

• S + O2 = SO2

- 2SO2 + O2 = 2SO3

Question 20

what kind of gases are sulfur dioxide and trioxide and what do they from when dissolved in water

Answer 20

• they are both acidic oxides
• when dissolved in water sulfur dioxide forms sulfurous acid
• and sulfur trioxide forms sulfuric acid

Question 21

what is the equation for the production of sulfurous acid and sulfuric acid

Answer 21

• SO2 + H20 = H2SO3 (sulfurous acid)

- SO3 + H20 = H2SO4 (sulfuric acid)

Question 22

what do both of these form in the atmosphere and what are its impacts

Answer 22

• they form acid rain
• which causes environmental damage
• to things like aquatic life and crops

Question 23

how are oxides of nitrogen formed

Answer 23

• under very high temperatures like in car engines
• nitrogen molecules can burn with oxygen molecules in the air
• to form various oxides of nitrogen

Question 24

what is the formula for an oxide of nitrogen and what are the most common ones

Answer 24

• NOx
• the common ones are nitrogen monoxide (NO)
• and nitrogen dioxide (NO2)

Question 25

at very high temperatures what is the main reaction between nitrogen and oxygen molecules (its equation)

Answer 25

N2 + O2 = 2NO

Question 26

since nitrogen dioxide is soluble in water, what two products does it form when reacting with water in the atmosphere what is the equation for this

Answer 26

• 2NO2 + H2O = HNO2 + HNO3

- nitrous and nitric acid

Question 27

are nitrous and nitric acid any different to sulfurous and sulfuric acid

Answer 27

• no

- they also make acidic rain which damages the environment

Question 28

what are catalytic converters

Answer 28

• pieces of machinery in vehicles
• built to reduce the amount of pollutants released
• by converting them into less polluting products

Question 29

what is the common build of a catalytic converter

Answer 29

• they contain platinum, rhodium and palladium in small quantities
• these are spread over a honeycomb mesh to increase the surface area

Question 30

what is a three-way catalyst

Answer 30

• a catalytic converter that can remove three different types of pollutants
• carbon monoxide
• oxides of nitrogen
• and unburned hydrocarbons

Question 31

how is carbon monoxide and unburned hydrocarbons converted to cleaner products

Answer 31

by oxidising them

Question 32

what would the oxidisation of carbon monoxide look like

Answer 32

2CO + O2 = 2CO2

Question 33

what would the oxidisation of an unburned hydrocarbon look like (C8H18)

Answer 33

C8H18 + 12.5O2 = 8CO2 + 9H20

Question 34

how are oxides of nitrogen converted and what is especially good about this reaction

Answer 34

• 2NO + 2CO = N2 + 2CO2

- its effective because it uses two polluting products to convert each other into cleaner ones

Question 35

can catalytic converters work on sulfur and what is the best way to prevent sulfur based polllution

Answer 35

• they dont really work
• so the best way to prevent pollution is to remove the sulfur compounds from the fuel
• before the fuel is burned

Question 36

what is fuel that has has its sulfur impurities removed called

Answer 36

• low sulfur fuel

- or ultra low sulfur fuel