Hydrocarbon: Compounds that contain atoms of carbon and hydrogen only.
- Saturated Hydrocarbon: is a hydrocarbon with single bonds only.
- Unsaturated Hydrocarbon: is a hydrocarbon with multiple Carbon=Carbon bonds.
- Aliphatic Hydrocarbons: Carbon atoms joined together in joint or branched chains.
- Alicyclic Hydrocarbons: Carbon atoms joined together in a ring structure.
F322: Organic Chemistry
Functional Groups: Part of the organic molecule responsible for its chemical reactions.
Homologous Series: A series of organic compounds with the same functional group but with each successive member differing by CH2.
- Alkanes: CnH2n+2 CH4, C2H6, C3H8 etc
- Alkenes: CnH2n C2H4, C3H6, C4H8 etc
F322: Fomulae of Organic Compounds
Emperical Formula: Simplest whole number ratio of atoms in a compound.
- e.g 85.63% C 14.37% H
- 12 1
- =7.14 =14.37
- 7.14 7.14
- Therefore CH2
Molecular Formula: Actual number of atoms of each element in a molecule.
General Formula: Simplest algebraic formula for a member of a homologous series.
- e.g Alkanes: CnH2n+2
- Alkenes: CnH2n
- Alcohols: CnH2n+OH
Displayed Formula: Relative positioning of all atoms in a molecules and their bonds.
- e.g Butane: C4H10: C-C-C-C with hydrogens attached.
F322: Fomulae of Organic Compounds
Structural Formula: Minimal detail for the arrangement of atoms in a molecule.
- e.g Propane: C3H8: CH3CH2CH3
Skeletal Formula: is a simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving a carbon skeleton.
Structural Isomerism: Molecules with the same molecular formula but with a different structural arrangements of atoms.
Steroisomerism: Compounds with the same structural formula, but with a different arrangement of atoms in space.
E/Z Isomerism: Isomerism in which groups attached to each carbon of a C=C bond may be arranged differently in space because of the restricted rotation of the C=C bond.
CIS/TRANS: CIS=Z=Same Side TRANS=E=Opposite Sides
F322: Organic Reagents and their Reactions
Organic Reactions: During a chemical reaction bonds can be broken in 2 ways.
- Homolytic Fission: Breaking of a covalent bond with an electron going to each atom forming 2 radicals.
- Heterolytic Fission: Breaking of a covalent bond with both electrons going to one atom. 2 ions are formed. One positive (Cation) and One negative (Anion).
Nucleophile: An electron pair donor.
Electrophile: An electron pair acceptor.
F322: Organic Reagents and their Reactions
Addition Reactions: 2 reactants combine together to make 1 product. A molecule is added across the C=C bond of an unsaturated molecule to make a saturated molecule.
C2H4 + Br2 >>> C2H4Br2
Substitution Reactions: An atom or group of atoms replaced by a different atom.
C2H5Br + OH- >>> C2H5OH + Br-
Elimination Reaction: 1 reactant to form 2 products. Molecule is removed from a saturated molecule to make an unsaturated molecule.
C2H5OH >>> C2H5 + H20
F322: Hydrocarbons as fuels
Fractional Distillation: Separation of components in a liquid mixture into fractions which differ in boiling point by means of distillation.
- Short-chained hydrocarbons with lower boiling points condense near the top.
- Long-chained hydrocarbons with higher boiling points condense near the bottom.
- Gases don't condense and pass through an outlet at the top: petroleam gas.
Boiling Points of Alkanes: Alkanes have weak intermolecular forces of attraction between molecules called VDW's. In order to boil these forces must be broken.
- Effect of Chain Length: As chain length increases, boiling point increases as intermolecular forces get stronger. There are more points of contact, therefore more VDW's and more energy required to seperate molecules.
- Effect of Branching: Branched isomers have a lower boiling point than unbranched ones. Fewer points of contact therefore less VDW's. Can't get as close together. Less energy is required to separate molecules.
F322: Hydrocarbons as Fuels
Combustion of Alkanes:
- Complete: CH4 + 202 >>> CO2 + 2H20
- Incomplete: C8H18 + 8.502 >>> 8CO + 9H20
Cracking: Refers to the breaking down of long-chained saturated hydrocarbons to form a mixture of short chain alkanes and alkenes.
- Catalytic cracking uses a zeolite catalyst at 450 degrees.
- C12H26 >>> C10H22 + C2H4
F322: Fossil Fuels and Beyond
- Carbon Monoxide: Toxic gas formed by incomplete combustion.
- Carbon Dioxide: Major contributor to global warming.
- Nitrogen Oxides: Contributes to acid rain and destruction of forrests.
- Sulfur Dioxide: Contributes to acid rain.
Global warming: a graual increase in the earths average temperature.
F322: Substitution Reaction of Alkanes
Mechanism for Chlorination (Radical Substitution):
1) Cl-Cl bond is broken by homolytic fission (UV Light) forming 2 Cl radicals.
2) (i) Methans reacts with a Cl radical. A CH bond breaks forming a methyl radical. HCl is also formed.
(ii) The methyl radical reacts with Cl2 forming a Cl radical and CH3Cl.
3) 2 radicals combine to form a molecule.
- 1) Cl-Cl >>> Cl- + Cl-
- 2) (i) CH4 + Cl- >>> CH3- + HCl
- (ii) CH3- + Cl2 >>> CH3Cl + Cl-
- 3) (i) Cl- + Cl- >>> Cl2
- (ii) CH3- + CH3- >>> C2H6
- (iii) CH3- + Cl- >>> CH3Cl
- where - = a radical.
Alkenes: are hydrocarbons with at least one C=C bond. General formula = CnH2n.
Double Bond: Made up of 2 parts: sigma bonds and Pi bonds.
- The double bond is formed via the sideways overlap of P-Orbitals forming Pi bonds.
- A Pi bond is the reactive part of the double bond.
- Pi bonds are formed above and below the plane of bonded atoms.
- Pairs of electrons repel each other as far as possible. This means there is restricted rotation around the bonds.
Alkenes are more reactive than alkanes due to the double bond. The difference in enthalpies (612-347=265KJ mol) reflects the strength of the Pi bond.
Pi bonds are weaker than Sigma bonds, when an alkene reacts the Pi bond breaks and the Sigma bond remains intact.
F322: Reactions of Alkenes
When a small molecule is added across the double bond causing the Pi bond to be broken. 2 reactants react together to form 1 product. An unsaturated alkene reacts and forms a saturated product.
- Addition of Hydrogen: H2 gas and gaseous alkene passed over a Ni catalyst @ 150 degrees. C2H4 + H2 >>> C2H6.
- Addition of Halogens: Alkenes react rapidly with halogens. When Br reacts with alkenes the colour changes from orange to colourless. This indicates Br has reacted with the double bond. C2H4 + Br2 >>> C2H4Br2.
- Addition of Hydrogen Hallides: A hydrogen hallide adds across the double bond to produce a halogenoalkane. C2H4 + HBr >>> C2H4HBr.
- Addition of Steam: High temperatures and pressure with a Phosphoric acid catalyst. C2H4 + H20 >>> C2H5OH.
F322: Further Addition Reactions of Alkenes
Electrophillic Addition Reactions: The double bond in alkenes represents a region of high electron density due to the Pi electrons in the double bond. Electrophiles are attracted to these Pi electrons.
- Addition of HBr: HBr is a polar molecule. Br is more electronegative than H inducing a dipole. H+ and Br-. An electron pair is attracted to the H+.
- Addition of Br2: Br is non-polar. When it approaches an alkene the Pi bond electrons repel the Br2 molecule, inducing a dipole, the reaction can then proceed. (Heterolytic Fission).
Polymers: Long molecular chain built up from monomer units. A monomer is a small molecule that combines with many other monomers to form a polymer.
- Addition Polymerisation: Monomers add to a growing polymer chain one at a time, to form a saturated molecular chain.
- Radical Polymerisation: Requires temperatures of 200 degrees and high pressures. It leads to branching of the polymer chain and polymer mix's.
- Ziegler-Natta Process: Involves the use if catalysts (TiCl3 @ 60 degrees). Alkenes pass over the catalyst, low conversion and any unreacted alkene is recycled. Used to manufactue unbranched polymers.
- Monomers are unsaturated: e.g. C=C.
- Polymers are saturated: e.g. C-C.
F322: Making and Using Alcohol
Hydration of Ethene: Manufactured industrially by the catlytic hydration of Ethene. Steam in the prescence of a CONC H3PO4 catalysts.
C2H4 + H20 >>> C2H5OH
Fermentation: Carbohydrates are heated at low temperatures in the prescence of yeast at 25 degrees. (anything above 37 degrees denatures the enzymes.) Toxicity of alcohol also limits the CONC of ethanol as if it is too strong enzymes can denature. (14%)
C6H12O6 >>> 2C2H5OH + 2CO2
F322: Properties of Alcohols
Physcial properties of alcohols are influenced by their ability to form hydrogen bonds between the OH groups of neighbouring molecules.
Volatility and Boiling Point: Hydrogen bonds are the strongest type of intermolecular forces. Thus alcohols have relativley high melting boiling points and low volatility. They dissolve in water because hydrogen bonds form between the polar OH groups of the alcohol and water.
- Primary Alcohols: The OH group is attached to carbon atoms with no alkyl groups or 1 alkyl group.
- Secondary Alcohols: The OH group is attached to a carbon atom with 2 alkyl groups.
- Tertiary Alcohols: The OH group is attached to a carbon with 3 alkyl groups.
F322: Combustion and Oxidation of Alcohols
Alcohols can be oxidised using an oxidising agent (O): e.g K2Cr2O7.
Primary Alcohols: Can be oxidised to produce an aldehyde. On stronger heating a carboxlic acid will form.
- CH3CH2CH2OH + (O) >>> CH3CH2CHO + H2O (DISTILLATE)
- CH3CH2CH2OH + 2(O) >>> CH3CH2COOH + H20
Secondary Alcohols: Can be oxidised to produce a ketone.
- CH3CH(OH)CH2CH3 + (O) >>> CH3COCH2CH3 +H2O
F322: Esterification of Alcohols
Esterification: An ester is formed when an alcohol is warmed with a carboxylic acid:
e.g CH3CH2COOH + CH3OH >>> CH3CH2COOCH3 + H20
Dehydration: An alcohol can be dehydrated to form an alkene in the prescence of an acid catalyst. (Elimination Reaction) Saturated molecule forms an unsaturated molecule.
e.g CH3CH2OH >>> C2H4 + H20
Compounds in which a halogen atom has replaced at least 1 hydrogen atom in an alkane. General formula: CnH2n+1X. Where X = A halogen.
Reactivity: Halogenoalkanes contain a polar carbon-halogen bond due to their different electronegativities. Electronegativity of halogens decreases down the group. The elctron-deficient carbon attracts nucleophilles (H20, OH-, NH3).
Hydrolysis: When they react with hot hydroxide ions, nucleophillic substitution occurs.
C2H5CH2I + OH- >>> C2H5CH2OH + I-
F322: Rate of Hydrolysis
Polarity VS Bond Enthalpy:
- Polarity: Carbon-Fluorine bond is the most polar. Should attract nucleophilles the most readily.
- Bond- Enthalpy: Carbon-Iodine bond is the weakest. This bond should be broken most easily and give the fastest reaction as it is weaker.
Bond enthalpies are more important in the rate of hydrolysis.
Halogenoalkanes and the Environment:
CFC's: When under UV light CFC's break down forming Cl radicals. These radicals catalyse the break down of ozone O3.
Alternatives: HFC's and HCFC's are both non-flammable and non-toxic but they still deplete the ozone layer but at 1/10th the rate.
F322: Percentage Yield and Atom Economy
Percentage Yield: 100% yields are rarely obtained becuase:
- the reaction may not go to completion.
- side reactions may occur.
- reactants aren't pure.
(Actual amount / Theoretical Amount) * 100 = % Yield.
(Molecular Mass of Desired / Molecular Mass of All) * 100 = Atom Economy
F322: Infrared Spectroscopy
All molecules absorb infrard radiation. This energy makes bonds vibrate with either a stretching or bending motion.
Every bond bends at it's own unique frequency. This is dependent on:
- Bond Stength.
- Bond Length.
- Mass of each atom involved in the bond.
F322: Mass Spectrometry
Uses: to identify unknown compounds, to determine abundance of each isotope in an element and to gain more knowledge on the structure/properties. It is also use to monitor patients breathing rates; detecting banned substance and space analysis.
Key Features: Number of peaks = number of isotopes, heights of peaks gives relative abundances.
When an organic compound is placed in a mass spectrometer, molecules lose electrons and are ionised. This is the molecular ion. M+. It has the same mass as the compound. Excess energy from the ionisation can be transfered to the molecular ion, making it vibrate. This causes bonds to weaken and the molecular ion can be split into pieces by fragmentation.
Fragmentation: process in mass spec that causes a +ive ion to split into pieces.
F322: Mass Spectrometry
Fragmentation results in a positive fragment ion and neatral species. e.g C2H5OH+ >>>CH3 + CH2OH+. Fragment ions are often broken up further into smaller fragments.
The molecular ion and fragment ions are detected in the mass spectrometer. The molecular ion produces the peak with the highest M/Z value.
Fragmentation Patterns: Although the molecule ion peak of isotopes will have the same M/Z value, fragmentation patterns will be different.
- 15 CH3+
- 29 C2H5+
- 43 C3H7+
- 57 C4H9+
Enthalpy is the heat content stored in a chemical system.
- Exothermic Reaction: give out energy to surroundings, system heat loss. Delta H is negative. (Temperature is increased.).
- Endothermic Reaction: take energy from surroundings, system gains heat. Delta H is positive. (Temperature is decreased.).
F322: Standard Enthalpy Changes
Standard Conditions: 101kPa/1atm, 25 degrees/298K and CONC 1 mol dm(-3).
Standard Enthalpy Change of Combustion: the enthalpy change that takes place when one mole of a compound reacts completely with oxygen under standard conditions. Reactants - Products
Standard Enthalpy Change of Formation: the enthalpy change that takes place when one mole of a compound is formed from its constituent elements under standard conditions. Products - Reactants
Standard Enthalpy Change of Reaction: the enthalpy change that accomponies a reaction in the molar quantities expressed in a chemical equation under standard conditions.
Average Bond Enthalpy: is the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous space. Reactant - Products
F322: Determination of Enthalpy Changes
Q=MC delta T
- M = mass of compounds involved.
- C = Specific Heat Capacity (of water = 4.18).
- Delta T = Temperature Change (Final - Initial).
F322: Rates of Reaction
Rate of Reaction is the change in concentration of a reactant or product in a given time.
rate = (change in concentration/time) mol dm(-3) s(-1)
At then start, rate is fastest as each reactant has its greatest concentration. During, rate slows as concentrations of reactants decrease. End, when 1 of the reactants is used up the rates become zero.
Factors that alter rate:
- Increased Temp: More kinetic energy-more collisions-increased rate.
- Increased Pressure: Less space therefore more molecules in same space-more collisions-increased rate.
- Increased CONC: More molecules in same volume-more collisions-increased rate.
- Surface Area: More points of contact-increased rate.
Provide an alternative route for a reaction to occur with a lower activation energy.
- Heterogeneous: a reaction in which the catalyst had a different physical state from the reactants.
- Homogeneous: a reaction in which the catalyst and reactants are in the same physical state.
Many industrial processes rely on catalysts to reduce costs. Help create reactions with lower activation energies. Therefore less reliance on creating conditions. Overall this helps the environment by saving on resources.
- Effect of Temperature: More collisions take place, more kinetic energy therefore more molecules reach the activation energy.
- Effect of Catalyst: Lower activation energy therefore more successful collisions.
F322: Chemical Equilibrium
Dynamic Equilibrium: is the equilibrium that exists in a closed system when the rate of the forward reaction = rate of reverse reaction.
- A chemical system is in dynamic equilibrium when: the concentrations of products remain the same and the rate of forward reaction = rate of reverse.
- Equilibrium applies as long as the system remains isolated.
Adding a Catalyst:
- A catalyst doesn't alter the postion of equilibrium. A catalyst speeds up the rate of forward and reverse reactions. They increase the rate at which equilibrium is established.
F322: Chemical Equilibrium
Change in Concentration:
- increasing conc of reactants: Oppose change, equilibrium moves to RHS.
- increasing conc of products: Oppose change, equilibrium moves to LHS.
Change in Pressure:
- Increasing the pressure: Equilibrium moves to the side with fewer gas molecules.
- Decreasing the pressure: Equilibrium moves to the side with more gas molecules.
Change in Temperature:
- Increase in temp: Oppose change, equilibrium moves left - FORWARD REACTION = EXOTHERMIC.
- Decrease in temp: Oppose change, equilibrium moves right - FORWARD REACTION = ENDOTHERMIC.
F322: Chemical Equilibrium - The Haber Process
N2(g) + 3H2(g) <<>> 2NH3(g) Delta H = -91KJ Mol(-1)
- High Pressure as 4MOL(g) on LHS and 2MOL(g) on RHS. Equlibrium will move to the RHS as there are less MOL(g).
- Forward reaction is exothermic favored by a low temperature.
- High temperature.
- High Pressure.
- 400 Degrees, 200ATM and Fe catalyst.
F322: Global Warming Solutions and Air Pollution
Alternative Fuels: Wind turbines, tidal power, solar panels and nuclear plants.
Carbon-Capture-Storage: Capture CO2. It can then be stored in several different places. e.g: Old gas and oil fields; quaries and under the sea bed.
Carbon Monoxide: Poisonous gas emitted into the atmoshere. Causes serious health problems: bonds to haemoglobin in the red blood cells.
Oxides of Nitrogen: Helps the formation of Ozone. Contributes to acid rain. They are also respiratory irritants and effect asthmatics.
Unburnt Hydrocarbons: VOC's (volatile organic compounds) are released in vehicle exhaust gases.They contain human carcinogens. They also react with low level oxone which may cause breathing difficulties.
F322: The Ozone Layer
- Initiation: CFCl3 >>> Cl- + CFCl2-
- Propagation (1): Cl- + O3 >>> ClO- + O2
- Propagation (2): ClO- + O >>> Cl- + O2
- Termination: O3 + O >>> 202
- Initiation: NO2 >>> NO- + O-
- Propagation (1): NO- + O3 >>> NO2- + O2
- Propagation (2): NO2- + O >>> NO- + O2
- Termination: O3 + O >>> 202
F322: Catalytic Converter and Uses of CO2
The catalyst provides a surface on which the reaction takes place:
- The CO and NO gas molecules diffuse over the catalytic surface of the metal. The molecules are held on the surface by adsorption.
- Temporary bonds form between the catalyst and the gas molecules.
- The bonds hold the gas molecules in the correct position where they react. 2NO + 2CO >>> N2 + 2CO2.
- After the reaction, the CO2 and NO2 products are desorbed from the surface and diffuse away from the catalyst.
Uses of CO2:
- Used as a blowing agent to make foam. Carbon neutral process.
- Used as a solvent changing temperature and pressure. It becomes a suprecritical fluid - scCO2.
- scCO2 is used to remove caffeine from decaf coffee.
- scCO2 is used to extract the characteristic flavour of beer.