Developing Fuels Flashcards
What is a π bond?
π bond is the sideways overlap of adjacent p orbitals above and below bonding atoms, there is restricted rotation (C=C bond)
What is a sigma bond?
The overlap of s orbitals between the two atoms, there is free rotation around the single sigma bond (C-C bond)
State the conditions for standard conditions
298K, 1M, 1 atm
Define Enthalpy change
The heat energy change under constant pressure
Why are alkenes more reactive than alkanes?
π bonds have lower bond enthalpy than sigma bonds, so require less energy to break them and react with another species.
C=C double bond is an area of high electron density, making it susceptible to attack by electrophiles.
Will the ∆H of an exothermic reaction be + or - ?
Exothermic ∆H= -
Endothermic ∆H= +
How does mean bond enthalpy relate to the strength and length of a bond?
Lower bond enthalpy means a weaker and longer bond.
Define enthalpy change of reaction.
The enthalpy change when quantities of substances in standard states react completely under standard conditions.
Define enthalpy change of formation.
The enthalpy change when 1 mol of a substance is produced from its constituent elements under standard conditions.
Define enthalpy change of combustion.
The enthalpy change when 1 mol of a substance is burned completely in oxygen under standard conditions.
Define enthalpy change of neutralization.
The enthalpy change when solutions of acid and alkali react together under standard conditions to produce 1 mol of water.
Equation linking energy change, specific heat capacity…
q = mc∆T Energy change (q) = mass x specific heat capacity x temp. change
Define specific heat capacity
The energy required to raise 1kg of a substance by 1K without change of state.
State Hess’ Law
The total enthalpy change of a reaction is conserved regardless of the route taken.
What is the role of catalysts?
Catalysts speed up the rate of reaction by lowering the activation energy by providing an alternate reaction pathway
What are heterogeneous catalysts?
Catalysts in a different state or phase than the species in the reaction
How does a heterogeneous catalyst work?
A solid heterogeneous catalyst adsorbs molecules onto the active site on the surface, increasing proximity and weakening covalent bonds in the molecules, allowing the reaction to occur more easily and faster.
What is catalyst poisoning?
When impurities in the reaction mixture bind to the catalyst’s surface, blocking the adsorption of molecules, reducing the activity of the catalyst.
What is cracking?
The process of converting long chain hydrocarbons into shorter, useful hydrocarbons by breaking carbon-carbon bonds (often producing alkenes as well).
Explain the two processes of cracking.
Thermal cracking uses high pressure and temp., catalytic cracking produces aromatic compounds as hydrocarbon vapor is passed over a heated catalyst often at lower temp. (720K) and regular pressure.
Why are hydrocarbons (alkanes) good fuels?
They release a lot of energy and, with sufficient oxygen, fully combust.
Explain what incomplete combustion is. What are the products?
If oxygen is insufficient, incomplete combustion occurs. Products vary, can include C, CO, CO2, + H2O depending on oxygen levels.
Explain why CO is dangerous.
It is a toxic, odorless gas which replaces oxygen in red blood cells, starving brain & organs with oxygen, leading to suffocation.
What are the other byproducts of alkane combustion, and how are they harmful?
Nitrogen and sulfur oxides react with water in clouds to produce acid rain, damaging buildings, lakes and wildlife.
Carbon particulates of unburnt fuel can cause respiratory problems and global dimming.
What is a catalytic converter and what is it used for?
This involves a rhodium catalyst to convert harmful particulates (CO, NOx, etc.) into stable products such as H2O and CO2.
Define a hydrocarbon.
Compounds containing only carbon and hydrogen atoms.
Define functional group.
A specific group of atoms or bonds within a compound that is responsible for the characteristic chemical reactions of that compound (i.e. alcohol -OH)
Define homologous series.
A family of hydrocarbons with similar chemical properties who share the same general formula (i.e. CnH2n - alkene). (Increase in boiling point as chain length increases).
What is the difference between aliphatic and aromatic compounds?
Aliphatic compounds are straight or branched carbon chains.
Aromatic compounds contain benzene rings.
Explain the naming system for alkanes.
Stem - longest carbon chain prefixes: 1(meth-), 2(eth-), 3(prop-), 4(but-), 5(pent-), etc.
Functional group suffix: alkane (-ane), alkene (-ene), alcohol (-ol), cycloalkane(cyclo-)
Halogen prefix: F(Fluoro-), Cl(Chloro-), Br(Bromo-), I(Iodo-)
Side chain alkyl groups C chain number: 1(methyl), 2(ethyl), etc.
Side chain number given from closest to first C
More than one side chain/functional group prefix: 2(di-), 3(tri-), 4(tetra-), etc.
E.g. 2,2-dimethylpropane
Describe the structure of a benzene ring.
Benzene (C6H6) is a ring of 6C each bonded to one H, with a ring of delocalized electrons
What is a saturated and unsaturated compound?
Saturated: Contain C-C single bonds only
Unsaturated: Contain C=C double bonds, triple C bonds, or an aromatic ring.
What is an alkene?
An unsaturated hydrocarbon with at least one C=C double bond, part of a homologous series of CnH2n.
Explain the naming system for alkenes.
Identify longest C chain with C=C bond, counting closest to C=C bond, following prefix rule like alkanes
Suffix of 1-ene, 2-ene, etc. wherever double bond is.
Side chains prefix like alkanes
E.g. 4-methylhex-1-ene
What is the order of priority of alkene naming suffixes?
(Highest to lowest): Carboxylic acid (-anoic acid), aldehyde (-al), ketones (-one), alcohol (-ol), alkene (-ene), haloalkane (-ane)
What is an electrophile? Give examples of common electrophiles.
An electron acceptor that is attracted to areas of high electron density.
E.g. HBr, Br2, H2SO4
Describe a test for the presence of alkenes.
Bromine water changes color from orange-brown to colorless when an alkene is present, as the C=C bonds ‘open up’ to accept Br atoms, becoming a saturated dibromo compound.
What is an electrophilic addition reaction?
The reaction mechanism showing how electrophiles ‘attack’ alkene C=C double bonds
Describe the electrophilic addition reaction of alkene with Br2.
As Br2 approaches alkene, π bond electrons repel electron pair in Br-Br bond, inducing a dipole, Br2 becomes polar and electrophilic. The intermediate has formed, with a C+ carbocation. Br bonds with carbon, forming dibromoalkane.
What is Markownikoff’s Rule?
Bromine will be added to carbon with fewest Hydrogens attached to it. Because
What are the 4 main types of electrophilic addition reactions?
1) Hydrogenation: using a nickel catalyst, producing an alkane
2) Halogenation: producing a monohaloalkane
3) Halogenation: producing a dihaloalkane
4) Hydration: producing an alcohol under high temp. (300-600ºC) and high pressure (70atm) with concentrated phosphoric acid (H3PO4) catalyst.
What is a stereoisomer?
A compound with the same structural formula but a different spatial arrangement of atoms and bonds.
What is an E and Z isomer?
E isomer is when H atoms are on alternating sides.
Z isomer is when H atoms are on the same side.
What is a nucleophile?
An electron pair donor, it is electron rich so attracts electrophiles.
Explain how E/Z isomerism arises.
Due to limited rotation of π bond in C=C double bond, so H atoms are either on alternating or the same sides.
Explain how E/Z isomerism affects physical properties of compounds.
Z isomers have H atoms on the same side, which have a partial + charge, creating a polar compound.
E isomers have alternating side H atoms, creating a non-polar compound.
State the ideal gas equation
pV = nRT p = Pressure in Pa V = volume in m3 T = temperature in K n = moles R = gas constant = 8.314 J/K/mol
