Developing Fuels Flashcards
State the standard conditions.
- Standard temperature - 25°c (298K)
- Standard pressure - 1atm
- Standard concentration - 1 mol dm-3
- Standard state - s,l,g
Define system
The reactants + products being measured (inside the reaction vessel)
Define surroundings
Everything else that’s not the system - outside the reaction vessel
Define exothermic
A reaction that gives out energy from the system to the surroundings and heats them.
Define endothermic
A reaction that takes energy into the system from the surroundings, cooling the surroundings.
What is thermochemistry?
The study of the energy + heat associated with chemical reactions.
Why type of process is bond breaking?
Endothermic as it requires energy
What type of process is bond forming?
Exothermic as energy is released
What formula is used to measure enthalpy change?
E = mcΔT
What do experiments to measure enthalpy changes ususally involve?
Transfering energy to/from water
What general formula can be used to calculate ΔH of a reaction?
ΔH = Hproducts - Hreactants
What is an alkane?
A saturated hydrocarbon
What are the 4 main features of alkanes?
Have the general formula CnH2n+2
Have names ending in -ane
Are saturated - each C is bonded 4 times with the maximum number of hydrogens possible.
Are aliphatic - don’t contain benzene rings
What do dashed/dotted bonds represent in the 3D structure of a molecule?
A bond in the direction behind the plane of the paper
What do wedges represent in the 3D structure of a molecule?
A bond in the direction in front of the plane of the paper
What does aromatic mean?
An organic molecule/hydrocarbon containing 1+ benzene rings
What does aliphatic mean?
Straight unbranched non-aromatic chains.
What is a functional group?
A modifier responsible for the characteristic chemical reactions/behaviours of molecules that contain it
What is a homologous series?
Series of compounds in which all members have the same functional group but have different carbon chain lengths
What is a cycloalkane?
A saturated hydrocarbon where the carbon atoms are joined in a ring
What are the 5 main features of a cycloalkane?
Have the general forumla CnH2n
Have names begining with cyclo-
Have names ending in -ane
Are saturated - 2 hydrogens per carbon
Are aliphatic
What is an alkene?
An unsaturated hydrocarbon containing 1+ C=C bonds
Describe the bonding in an alkene
A C=C bond contains a sigma (σ) bond and a pi (π) bond.
A σ bond is an area of increased e- density between the C atoms. Only contains 1 area of negative charge
A π bond consists of 2 areas of negative charge. One of these is above the line of the atoms and the other is below
What are the 5 main features of alkenes?
Have the general formula CnH2n (for 1 double bond)
Have names ending in -ene
Are unsaturated - Have 1+ double covalent bonds between C atoms in molecule
Are aliphatic - don’t contain benzene rings
Double bonds have a high electron density making alkenes fairly reactive.
What are arenes?
A group of organic molecules with benzene rings. The electrons in the double bonds are not attached to a particular carbon so are delocalised. Shown by a circle in 6 carbon skeleton.
Where are σ bonds found?
Where are π bonds found?
σ bonds found in single bonds
π bonds found in double bonds (along with a σ bond)
What are the bond angles around the C=C bond?
All bond angles around C=C bond 120º
Because there are 3 groups of e- around each C atom - 2 single bonds + 1 double bond
These groups repel each other as far as possible
How are alcohols produced?
- By the hydration of alkenes
- From alkyl hydrogen sulfate
What is an electrophile?
A positive ion or molecule with a partial positive charge on one of the atoms which causes it to be attracted to a negatively charged area.
It will react by accepting a lone-pair to form a dative covalent bond
What is electrophilic addition?
A reaction in which an electrophile joins onto an alkene/molecule with double/triple bond
No atoms are removed from the alkene/molecule it joins on to
When is a covalent bond said to be polarised?
If the electrons are unevenly distribute between the atoms
What is a carbocation?
A molecule containing a carbon that has a positive charge
It is formed as an intermediate in electrophilic addition
What is copolymerisation?
When more than one type of monomer is used during polymerisation
Polymers have the general structure:
-A-B-A-B-A-B-
What are the conditions for addition polymerisation?
With a Pt catalyst - room temp + pressure
With a Ni catalyst - high temp + pressure
(100-200ºC + 2-10atm)
What is a structural isomer?
What are the 3 types of structural isomerism?
Molecules with the same molecular formula but which have different structural formulae
3 types: chain isomerism, position isomerism, functional group isomerism
What is chain isomerism?
The different arrangement arrangement of carbon atoms in a chain.
Chain lengths are different/carbons are in different places in the chain because of branching
What is position isomerism?
Where the functional group is situated in different places/potitions in the molecule
What is functional group isomerism?
Compounds have the same molecular formulae but have different functional groups
What is stereoisomerism?
Molecules with the same molecular formula but different arrangements of the atoms in space (different 3D structure)
Excludes any different arrangements due to the molecule rotating as a whole or rotating about particular bonds.
What specific type of stereoisomerism do you need to know about?
cis-trans/E-Z isomerism
What is needed for stereoisomerism to occur?
A double bond between 2 carbon atoms
2 different groups on each double-bonded carbon
In terms of stereoisomerism, what does cis- mean?
Groups on the same side of the double bond.
(When we don’t have 2 H’s)
In terms of stereoisomerism, what does trans- mean?
Groups on opposite sides of the double bond
(When we don’t have 2 H’s)
In terms of stereoisomerism, what does E- mean?
The highest priority groups are on opposite sides of the double bond.
In terms of stereoisomerism, what does Z- mean?
The highest priority groups are on the same side of the double bond
(think zame zide…)
What is Hess’ Law?
ΔH for any reaction will be the same regardless of any intermediate stages provided the start + end conditions/points are the same.
What is energy density?
The amount of energy produced per kg of fuel.
Define bond enthalpy
The energy required to break 1mol of a particular bond. Averaged over a range of different gasous compounds containing that bond
Why are theoretical calulcations for bond enthalpies often diferent to experimental results?
Average bond enthalpies from several compounds are used in the caluclation - the actual bond enthalpies in particular molecules will be vary slightly
Bond enthalpy data are for gaseous molecules - some molecules may be in different states (e.g. liquid) at 298K
Does a higher bond enthalpy mean a longer or shorter bond?
The higher the bond enthalpy, the shorter the bond
Define cracking
A reaction that breaks large molecules into smaller ones.
What is a catalyst?
Substance which speeds up the rate of chemical reaction by providing an alternate reaction pathway with a lower EA
Is not chemically changed/used up at the end of the reaction
(Although may form intermediates or be poisoned)
What is catalysis?
The acceleration of a chemical reaction by a catalyst
2 types - heterogenous + homogeneous
What is a catalyst poison?
How do they work?
A substance which irriversibly binds to the catalyst surface, blocking its active site and stopping it from functioning properly
Prevents/inhibits other/fewer reactants being adsorbed so the catalyst becomes less efficient
What type of catalyst is a catalytic converter in a car an example of?
Why?
A heterogeneous catalyst
The reactants are the exhaust fumes whilst the catalyst is a solid (finely-divided) metal (e.g. Pt/Rh)
Describe the mechanism of heterogeneous catalysis
Reactants come into contact with catalyst surface
Reactants adsorbed onto catalyst surface. This weakens intramolecular bonds
New bonds form, creating the products of the reaction
Products diffuse away from the catalyst surface, leaving it free for new reactants to adsorb to
What is a primary pollutant?
A pollutant released directly into the atmosphere.
What is a secondary pollutant?
A pollutant not released directly into the atmosphere
Instead formed from primary pollutants in the atmosphere
What goes into a car engine?
What comes out?
In: fuel + air
Out: CO2, CO, H2O, SOx, NOx, N2, particulates, unburnt hydrocarbons
What is photochemical smog?
Smog containing mix of primary + secondary pollutants which absorb light energy and undergo chemical reactions, forming smog
What are the effects of photochemical smog?
- Produces ozone + other secondary pollutants/irritating chemicals
- Ozone is a greenhouse gas + damages lung tissue/immune system
- Haziness + reduced visibility
- Eye + nose irritation
- Difficulty breathing
- Harmful to plants + animals
- Damages substances with C=C bond (e.g. plastic + rubber)
What are particulates, how are they produced, what effects do they have?
Small carbon particles smaller than 2.5x10-12m
Formed from burning fossil fuels + volcanoes
Penetrate the body causing lung cancer + heart attacks
Make surfaces dirty
