Developing Fuels Flashcards
What does exothermic mean?
It means that energy is given out
What does endothermic mean?
It means that it takes energy from its surroundings
Describe enthalpy change
This is the energy transferred to/from the surroundings to/from the reaction
What does the enthalpy level diagram for an exothermic reaction look like?
A high line on the left and a low line on the right with an arrow downwards
What does the enthalpy level diagram for an endothermic reaction look like?
A Low line on the left and a high line on the right with an arrow upwards
What is the equation to find enthalpy change?
ΔH = Hproducts - Hreactants
What is the ΔH for an
a) endothermic reaction
b) exothermic reaction
a) ΔH is positive
b) ΔH is negative
What does the ‘system’ mean?
It is the reaction
What can affect the ΔH value
Temperature
Pressure
Concentration
What are the standard conditions
1 atm pressure
298K = 25*C
Symbol: ΔHΘ298
What is the SI Unit for temperature? and what is 0*C
Kelvin
0*C = 273K
What is the equation to measure enthalpy change?
Energy transferred = SHC x mass x temperature change
What is specific heat capacity?
It is the energy required to raise the temperature of 1 gram of substance by 1*C
What is the specific heat capacity of water?
4.18 Jg-1K-1
What is the symbol for enthalpy change of combistion?
ΔcH
Is there standard enthalpy changes for combustion and how does it work?
The standard enthalpy change of combustion is possible and only works by adjusting the values to make for the standard temperature.
ΔcHΘ298
What is the standard enthalpy change of formation? What is the symbol?
This is the enthalpy change when 1 mole of a compound is formed from its reactants
Symbol: ΔfHΘ298
What is the standard enthalpy change of neutralisation? What is its symbol?
This is the enthalpy change when acid reacts with alkali and neutralises
Symbol: ΔneutHΘ298
What is the equation for a hess cycle?
ΔH1 = ΔH2 - ΔH3
How does a hess cycle work?
To work out the enthalpy change of a reaction you can use data from a different reaction route.
The overall enthalpy changes of the separate routes should be equal.
Often the enthalpy of formation of the reactants and products is used.
What is the equation that can be used to work out the enthalpy change of a reaction using data from the enthalpy change of formation?
ΔrH = ΣΔfHproducts - ΣΔfHreactants
What is an alkane?
It is hydrocarbon that has only single bonds
What is a hydrocarbon?
It is a molecule that only contains hydrogen and carbon
What is an aromatic compounds?
It is a compound that contains a benzene ring
What does aliphatic compound mean?
It means that there is no benzene ring
What is a molecule with a ring of 6 carbons called?
Arenes
Are hydrocarbon reactive?
No they are unreactive
What is a functional group?
It is a group that is added to a hydrocarbon that changes its properties
What is an alcohol?
It is a hydrocarbon with an -OH group on it
What is an alkene?
It is a hydrocarbon with at least 1 double bond
What does the term saturated and unsaturated mean?
Saturated means that the hydrocarbon has all single bonds along the carbon backbone
Unsaturated means that there are double bonds
What is a homologous series?
It is a group of compounds that are all related to each other.
e.g. Methane, ethane, propane, butane
What is a shortened structural formula?
It is like a full structural formula but the hydrogens are not written with a bond instead they just come after the carbon.
What is a branched alkane?
It is where the chain of carbons is not in a line and instead it has a carbon with two carbons around it so it looks branched
e.g. CH3 - CH2 - CH(CH3) - CH3
What is a structural isomer?
It is a molecule with the same molecular formula but a different structural formula
What are systematic names?
This is a way of naming hydrocarbons based off a set of agreed rules
What are cycloalkanes?
They are alkanes that connect together at each end to make a complete ring.
They have the prefix of cyclo
What are the steps to naming an alkane?
- Find the longest chain of carbons and name it
- Identify any side chains and name them
- Add -yl to their prefix and add it to the beginning of the name
- Add the carbon number that the carbon is attached to to the beginning to the name. Keep the number low
- If there are more than 1 side chain name them in alphabetical order
- If there are more than 1 of the same side chain then add di, tri or poly and also add the number of the carbons that those are attached to
e. g. 2 - methyl - pentane
How are cycloalkanes named?
- Count the number of carbons in the cyclic structure and name it
- Add cyclo to the beginning
What are the properties of alkanes?
1-4 Carbons: colourless gas
5-16 Carbons: Colourless liquids
17+ carbons: white waxy solids
They all mix well with each other but done mix well with water
What is a bond?
It is an electrical attraction between two atoms and breaking the bond involves overcoming the attraction
What is a bond enthalpy?
It is the amount of energy that it takes to break a bond
Talk about bond enthalpy and length?
Every bond has an equilibrium position which is the position with the shortest distance and the lowest energy
If the distance is greater, the attraction is greater than the repulsion.
If the distance is shorter then there is a strong repulsive force.
The shorter the bond length…
The stronger the attraction between atoms
Why are bond enthalpies average?
Because the bond length changes between different molecules
What is the bond enthalpy of a double bond vs a single bond?
A double bond is much stronger because there are more charges involved
How can bond enthalpies be used?
Using information, you can work out the energy in the bonds at the beginning (in the reactant) and at the end (in the products) then this information can be used to work out the energy to start a reaction or the energy given out by a reaction.
This is a bond enthalpy cycle
What is a catalyst?
It is a substance that speeds up the rate of a reaction by offering an alternative reaction bath that requires less energy. It is no involved in the reaction itself so it is not used up
What is a homogenous catalyst?
This is a catalyst that is the same state as what it is reacting with. this means that it has to be filtered out / removed after the reaction has completed
What is a heterogeneous catalyst?
It is a catalyst that is a different state from what it is catalysing.
What is the process for a heterogeneous catalyst?
- The reactants are adsorbed onto the surface of the catalyst by forming intermolecular bonds with it
- Reactants bonds between the reactants atoms break
- New bonds form between the reactants making the new products
- Then the new products are released by having the bonds between the catalyst and products weaken and broken and then the product is released
What is catalyst poisoning?
This is when the catalyst adsorbs a molecule that cannot be released from its surface. It permanently bonds with the molecule and poisons it. The active site is blocked.
What is an example of a process where catalyst poisoning is a problem?
In the production of hydrogen from methane. Trace amounts of sulfur react with the nickel catalyst and poisons it
What is an alkene?
It is a hydrocarbon that has at least one double bond.
Describe the bonding in a double bond on an alkene
There is a sigma (σ) bond and a pi (π) bond.
What is a sigma bond?
It is a standard single bond between s orbital electrons. It has one region of electron density
What is a pi bond?
It is part of a double bond and is formed when the electrons in the p orbitals overlap.
It consists of two areas of electron density, one above and one below the line of the atoms
What is a molecule that is attracted to negatively charged areas?
Electrophiles
Describe what electrophilic addition is and give an example using bromine.
When a bromine molecule approaches a double bond in an alkene, one of the bromine atoms in the molecule becomes partially positively charged and the other becomes partially negative.
This causes the electrons from the double bond to be attracted to the partially positive charge.
The electrons jump and form a bond with the partially positive bromine breaking the bromine molecules bond leaving the alkene to now be a single bond alkane with a positively charged carbon and a bromine with a negative charge (having excess electrons from the original Br2 bond)
Then the br- molecule bonds with the positive carbon to make a alkene with two bromines (1,2 - dibromoethane)
What is the difference between an addition and an electrophilic addition reaction?
An addition reaction is between two molecules and an electrophilic addition reaction is the same but one of the molecules is an electrophile
Describe the reaction between an alkene and hydrogen bromide?
It is the same as the bromine reaction but this time it is with hydrogen bromide
What is the addition reaction between ethene and water?
One of the hydrogens of the water molecule becomes partially positively charged and reacts with the double bond to form a bond. The OH- ion that is left then bonds with the C+ atom on the hydrocarbon to form an alcohol
What is formed with the addition reaction of an alkene with H2?
An alkane
Finish the equation:
CH2BrC+H2 + H20 ==>
CH2BrCH2OH + H+
What is a polymer?
It is a long molecule made up from lots of smaller molecules called monomers
Describe what addition polymerisation is? using propene as the example
This is when multiple monomers join together to make a larger polymer molecule. The double bond in propene breaks and joins with another molecule of propene and this continues to make a large polymer made from many monomers. Poly(propene) is produced
Because the same unit is repeated over and over again in a polymer, it can be shown as…..
[CH(CH3)-CH2]n
The monomer without the double bond can be placed into brackets with n being the number of monomers making up the polymer
What is copolymerisation?
This is when another monomer gets involved and ends up in the polymer chain.
What is the volume of 1dm3 in cm3?
1000cm3
What is molar volume and why does it work?
It is the volume that 1 mole of gas takes up in standard conditions. It is 24dm3
This works because equal volumes of all gasses at the same temperature and pressure contain the same number of molecules
What volumes of gasses are required for the reaction of N2 + 3H2 ==> 2NH3
1 units of volume of N2
3 units of volume of H2
2 units of volume of NH3
What is the ideal gas equation?
PV = nRT P = Pressure V = Volume n = Number of moles of gas R = The gas constant (8.31) T = Temperature in kelvin
What is the bond angle in alkanes?
109.5*
What is isomerism?
This is when two molecules have the same molecular formula but have a different arrangement of atoms. The isomers have different physical properties
What is chain isomerism?
This is when the carbon chain has a different structure. e.g. C4H10 can either be: CH3CH2CH2CH3 or CH3CH(CH3)CH3
What is positional isomerism?
This is when the position of the functional group changes. e.g. the carbon that the alcohol group is attached to changes
CH3CH2CH2OH
vs
CH3CH(OH)CH3
What is functional group isomerism?
This is when the functional group changes. An alcohol can have a functional group isomer that is an ether.
e.g. CH3CH2CH2OH vs CH3CH2OCH3
Describe sterioisomerism
Molecules with double bonds are unable to rotate around the double bond. This makes it fixed in place so the position of functional groups gives isomerism.
e.g. The position of the hydrogen on but-2-ene
What is the difference between E and Z isomerism? (cis and trans)
Z (cis) is when the functional groups are on the same side of the carbon double bond
E (trans) is when the functional groups are on different sides
How is stereoisomerism shown in the same of a compound?
E or Z or cis or trans is put at the beginning of the name
What properties can be affected by stereoisomerism?
Melting / boiling point
Density
How are alcohols named?
- name the prefix for the longest chain
- determine the position of the alcohol group
- Add ol to the end of the name
Name CH3CH(C2H5)CBrHCClHCH2OH
3-bromo-2-chloro-2-ethyl-pentan-1-ol
What are the products from complete combustion?
Carbon dioxide and water
What are the possible products from incomplete combustion?
Carbon Monoxide, Carbon and Water
Name the polluting effects of particulates
Penetrate deep into the body and can cause heart attacks and cancer. They also cause aesthma
Name the polluting effects of VOC and what is a VOC
VOC is a volatile organic compound
and it causes photochemical smog
Name the polluting effects of Carbon monoxide
It is a toxic gas and causes photochemical smog
Name the polluting effects of Carbon dioxide
It is a greenhouse gas
Name the polluting effects of Nitrogen oxides
They cause acid rain and photochemical smog
Name the polluting effects of Sulfer oxides
toxic gas and acid rain
How are sulfur oxides produced?
The burning of sulfur
S + O2 ==> SO2
How are nitrogen oxides produced?
The burning of nitrogen
N2 + O2 ==> 2NO
Use equations and describe how acid rain is produced from sulfur and how the strong the products formed are.
Sulfur oxides react with water to form acid rain:
SO2 + H2O ==> H2SO3 (weak acid rain)
SO3 + H20 ==> H2SO4 (strong acid rain)
What are the equations that make acid rain from nitros oxides and how strong is the acid rain?
It is a strong acid
2NO + H2O + 1.5O2 ==> 2HNO3
2NO2 + H20 + 0.5O2 ==> 2HNO3
What are the effects of acid rain?
It corrodes limestone buildings, causes breathing difficulties and kills forests and wildlife
What are the effects of photochemical smog?
When shone on by sunlight it causes haziness and reduced visibility and respiratory problems
How is carbon monoxide removed by a catalytic converter?
2CO + O2 ==> 2CO2
How are hydrocarbons removed by a catalytic converter?
C7H16 + 11O2 ==> 7CO2 + 8H2O
How is Nitrogen monoxide removed by a catalytic converter?
2NO + CO ==> N2 + 2CO2
How are sulfur oxides removed from exhaust fumes?
They are removed from the fuels before they are available to motorists
What is the equation where ammonia used to remove Nitros oxides from exhaust fumes?
4NO + 4NH3 + O2 ==> 4N2 + 6H2O
What are the alternatives to fossil fuels?
Biofuels
How can ethanol be made from biomass?
It can be made from the fermentation of carbohydrate crops
How is biodiesel made?
It is made by chemically reacting fats and oils with alcohol in a process called trans-esterification
What are the advantages of using biodiesel?
Can be made from waste oil It is carbon neutral Biodegradable if spilled Contains no sulfur Produces less particulates
What is the reaction for the combustion of hydrogen?
2H2 + O2 ==>2H2O
What are the advantages of using hydrogen as fuel?
It is renewable
Stored and sent down pipelines
Produces no carbon dioxide or carbon monoxide
What are the disadvantages of hydrogen as fuel?
It requires extraction using electricity generated from fossil fuels
Less energy dense
oxides of nitrogen are still produced
