Developing Fuels Flashcards
Standard Enthalpy Change for a Reaction
Enthalpy change when molar quantities of reactants, as stated in the equation, react together (standards conditions, standard states)
–> H(products) - H(reactants)
Standard Enthalpy Change of Combustion
Enthalpy change when 1 mole of a substance is burnt completely in oxygen (standards conditions, standard states)
(always negative)
Standard Enthalpy Change of Formation
Enthalpy change when 1 mole of a compound is formed from its elements (standards conditions, standard states)
Standard Enthalpy Change of neutralisation
Enthalpy change when 1 mole of H+ ions reacts with 1 mole of OH- ions to form water (standards conditions, standard states)
Hess’ Law
The total enthalpy change of a reaction is independent of the route taken so long as the starting point, end point, and conditions are the same.
Fractional Distillation
As you go up the column
- shorter chain
- lower melting/boiling point
Energy Density of a fuel
The amount of energy transferred by burning 1 kg of fuel
(1000 x /\cH) / Mr of fuel
In kJ/kg
Bond Enthalpy
The amount of energy required to break a bond in a molecule (also called bond dissociation enthalpy)
- requires overcoming the attractive forces between
the atoms or ions
- strength depends number of electrons involved, and
length
- Bond length is the at which electron +nuclei repulsion= nuclei + electrons attraction
Cracking
Reaction in which a large hydrocarbon is made into smaller hydrocarbons
Vapourised carbon passed over zeolite catalyst to produce shorter hydrocardbon vapours (collect in water thing)
Some of the products will be alkenes
Catalyst
A substance that speeds up a reaction by providing an alternate pathway with a lower activation enthalpy and is chemically unchanged at the end
Heterogeneous Catalysis
Reactant and Catalyst in different physical states
- Reactants adsorbed onto catalyst surface
- Bonds in reactants weaken and break
- New bonds form in products
- Products diffuse away from catalyst surface
Catalyst poisoning
Occurs when a molecule strongly adsorbs to the catalyst surface. Reaction cannot occur as the reactants can’t get to the surface
Can be regenerated
Electrophillic addition reactions (simple list)
Alkene + Bromine —> dibromoalkane (RTP)
Alkene + HBr —> bromoalkane (RTP)
Alkene + Hydrogen —> Alkane (150C, 5atm, Ni catalyst)
Alkene + Water —> Alcohol (H2SO4 catalyst)
Ideal gas eqation
pV=nRT
p- pressure in Pa V- volume in m^3 n- number of moles R- gas constant T- temperature in K
Gas theory
Equal volumes of gas at the same temperature and pressure contain an equal volume of moles. This is because the molecules in a gas are so far apart that it doesn’t affect the volume of the gas
1 mole of gas
- 24 dm^3 at RTP
- 22.4dm^3 at STP
Can then use Avogadro’s constant to find the number of molcules of gas
Isomerism
Isomers= molecules with the same molecular formula but the atoms are arranged differently
-Structural isomer (different structural formula_
> Chain isomers (C skeleton arranged differently)
> Position isomer ( functional group in different places)
> Functional group isomer (different functional groups
- Stereoisomer (differently in space)
>E/Z- E= trans, Z=Cis
> Optical isomer (PL)
Formation of Atmospheric Pollutants
Primary pollutant- released directly into atmosphere
Secondary pollutant- released indirecly into atmos
Carbon dioxide
- combustion of fossil fuels
- contributes to greenhouse effect)
Carbon monoxide
- incomplete combustion of fossils fuels, burning
biomass
-toxic gas, photochemical smog
Nitrogen oxides
- formed when N2 + O2 in the burn combine in the high
pressure and temperature of an engine/ power station
- N2 + O2 —> 2NO
- acid rain, photochemical smog
Sulfur oxides
- combustion of fossil fuels containing S compounds,
volcanoes (S + O2 —> SO2)
- toxic gas, acid rain
Particulates
- volcanoes, incomplete combustion, burning coal
- hear attacks, lung cancer, lung irritation
Volatile Organic Compounds (VOCs)
- plants, unburnt fuel in engines
- photochemical smog
Complete and Incomplete Comubstion
Complete: HC + Oxygen ---> Carbon dioxide + Water Alcohol " - occurs when there is lots of air available Incomplete: HC + (less) Oxygen ---> Water + CO (or C as soot) Alcohol " - occurs if oxygen supply is limited
Production of Acid Rain
From Sulfur Dioxide:
- SO2 enters atmos and reacts with water to form
sulfuric (iv) acid
> SO2 + H2O —> H2SO3
- SO3- oxidised to SO3 which reacts with water to form
sulfuric(vi) acid (stratosphere)
> SO3 + H20 —> H2SO4
From Nitrogen oxide and Nitrogen dioxide
- Both react with water and oxygen to from nitric(v) acid
> 4NO + 2H20 + 3O2 —> 2HNO3
> 2NO2 + 2H2O + O2 —> 2NHO3
Photochemical Smog
Occurs when primary pollutants are acted upon by sunlight to produce secondary pollutants
N oxides and unburnt HC from fuel react in the presence of sunlight to form ground level ozone. This combines with other compounds to form photochemical smog. The smog causes respiratory problems , reduced visibility and haziness
Catalytic Converters
Convert the main pollutants in exhaust (CO, HC, NO) into over compounds to remove them from the atmosphere.
Contain a Pt or Rh catalyst on honeycomb structure
2CO + O2 —> 2CO2
HC + O2 —> CO2 + H20
2NO + CO —> N2 + 2CO2
Alternative hydrocarbon fuels
Lignified Petroleum Gas (LPG) > comes from distillation of crude oil \+ can convert petrol engines easily, produces less CO2, Co, Nox and HC (lower road tax) - filling stations are rare - needs to be stored under pressure
Liquid Natural Gas (LNG)
> comes from oil and natural gas fields
- needs to be cooled below -160
+produces less CO and NOx
Biofuels
Biofuels are fuels derived from renewable plant and animal materials
Alternatives to fossil fuels- Hydrogen
Can build fuel cells that will convert chemical energy to electricity by reacting the O2 fuel with H2 oxidising agent within an electrochemical cell
2H2 + O2 —> 2H2O
+ H2 is renewable as made from electrolysis of water
+ Can be transported like methane
+ Can be used in internal combustion engine too
+ Doesn’t produce CO, CO2 or HC
- Cars need large volume of H2 so stored under high
pressure
- Production of H2 depends on electricity from fossil
fuels
- Less energy dense than fossil fuels
- NOx still produced at high temperatures
Alternatives to fossil fuel- Ethanol as a biofuel
Made by fermentation of carbohydrate crops, then mixed with petrol (too volatile alone
+Growing procedure is carbon neutral
- Need lots of arrable land to produce crops
- Enviro problems from disposal of fermentation waste
- Need to modify car engines
- land could be used for food
- uses energy from fossils fuels to produce and
distribute
Alternatives to fossil fuel- Biodiesel as a biofuel
Made by chemically reacting fats and oils with an alcohol to produce fatty acid esters ( and glycerol)
Reaction is called trans-esterification. Examples include biogas, and green diesel
+Can be made from waste oil
+Carbon neutral
+Don’t need to convert car engines if mix with regular
diesel
+Doesn’t contain S so no SOx
+Produces less particulates, CO and HC
-Produces more NOx than fossil fuels
