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A level chemistry > Developing Fuels > Flashcards

Flashcards in Developing Fuels Deck (26):
1

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)

2

Standard Enthalpy Change of Combustion

Enthalpy change when 1 mole of a substance is burnt completely in oxygen (standards conditions, standard states)
(always negative)

3

Standard Enthalpy Change of Formation

Enthalpy change when 1 mole of a compound is formed from its elements (standards conditions, standard states)

4

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)

5

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.

6

Fractional Distillation

As you go up the column
- shorter chain
- lower melting/boiling point

7

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

8

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

9

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

10

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

11

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

12

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

13

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)

14

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

15

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

16

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)

17

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

18

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

19

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

20

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

21

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

22

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

23

Biofuels

Biofuels are fuels derived from renewable plant and animal materials

24

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

25

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

26

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