Wider Impact Of Chemistry, Organic Molecules and Hydrocarbons Flashcards
Chemical process development must consider
Social implications (labour, use of land, impact on local amenities) and economic factors (industry plant sitation, transport, availability of services)
Cost of process
Research and development Capitol cost of plant Depreciation Labour costs Raw materials Energy costs Waste disposal costs Safety measures
Environmental factors
Impact on environment and energy consumption
“Polluter pays”
Green chemistry, manufacturers must
Keep waste to minimum
Use renewable resources if possible
Keep energy costs to a minimum
Catalysts so low temperatures can be used
Non toxic reactants if possible
Waste products treated to give non toxic materials
Alkene formula
CnH2n+2
Naming rules
Stem (meth, eth, prop….)
Suffix (ane, ene, yl, ol, oic acid, chloro)
Number the carbons from end closest to side chain
Count longest chain of Carbons
Alphabetical order
Alkane formula
CnH2n
Alkanes are..
Non polar due to tetrahedral shape and difference in electronegativity, they don’t dissolve in water as they can’t form hydrogen bonds, boiling point increases as chain length increases, branching in chain decreases boiling point
How do functional groups affect physical properties?
Boiling point affected by intermolecular forces type and strength
Non polar molecules have weak instantaneous dipole-induced dipole forces
Permanent dipole molecules have stronger dipole-dipole forces
N-H/F-H/O-H have hydrogen bonds
Hydrogen bonds in carboxyllic acids create a..
Dimer (2 molecules joined together)
Solubility in water for carboxyllic acids and alcohols
Highly soluble
Solubility decreases as chain length increases
Water cannot hydrogen bond with long hydrocarbon chains as they are hydrophobic
Structural isomers definition
Compounds with same molecular formula but different structural formula
Electrophile definition
Electron pair acceptor
Positive ions/positive part of polar molecule
Nucleophile definition
Electron pair donor
Negative ions/negative part of polar molecule
Radicals definition
Atom/molecule with an impaired electron, very reactive
Heterolytic bond fission
Covalent bond breaks, 2 electrons move into just one of the atoms
Results in positive and negative ions
E.g. Cl2–>Cl+ + Cl-
Homolytic bond fission
Covalent bond breaks, 2 electrons move into different atoms
E.g. Cl2–> 2Cl radicals
Hydrocarbons definition
Compound of only hydrogens and carbons
Bonds in alkanes
Strong
Non polar
Little polarisation (C and H similar electronegativities)
Tetrahedral arrangement negates any dipoles present
Weak van der waals
Alkanes are…
Unaffected by ions/polar molecules
Low melting and boiling points (weak Van der Waals)
Insoluble in water
Liquid alkanes are…
Good solvents for non polar molecules however don’t dissolve ionic or polar compounds
Combustion of alkanes
Good fuels- burn exothermically on presence of oxygen to produce CO2 and water vapour
Benefits to burning fossil fuels
Needed for transport, electricity generation, cooking, heating
Disadvantage of burning fossil fuels
CO2 (greenhouse gas) leads to global warming Can for SO2 which contributes to acid rain Limited supply of oxygen when burning = incomplete combustion forming CO (toxic gas) Not sustainable (crude oil non-renewable)
Halogenoalkanes formula
Alkanes + halogens –(UV light)–> halogenoalkanes
Halogenoalkanes is what type of reaction?
Substitution reaction (1 or more H atoms replaced with halogen)
Halogenoalkanes used as..
Dry cleaning solvents and refrigerants
No longer used as aerosol propellants as they damage ozone layer
Halogenoalkanes require UV light to make so is a …
Photochemical reaction
Photochlorination of methane equation
CH4(g) + Cl2(g) –(UV light)–> CH3Cl(g) + HCl(g)
Mechanism of Photochlorination of methane
Step 1- initiation UV light breaks Cl2 bond (Homolytic fission) Cl2--(UV light)--> 2Cl• Step 2- propagation CH4 + Cl•--> •CH3 +HCl Methyl radical reacts with Cl2 •CH3 + Cl2--> CH3Cl + Cl• Further substitution (2 further propagation steps) CH3Cl + Cl•--> •CH2Cl + HCl •CH2Cl + Cl2--> CH2Cl2 + •Cl Step 3- Termination 2Cl•--> Cl2 Cl• + •CH3--> CH3Cl 2•CH3--> CH3CH3
Hexane can be a product of Photochlorination of methane
2•C3H7–> C6H14
Formed from 2 radicals
Mechanism of reaction of halogens + alkanes in UV light
Radical substitution
C-H and C-C form
Sigma bonds
C=C bonds form
Pi bonds
E-Z isomerism
E = opposite Z = same
Which is E and Z isomers?
Look at 2 groups at one end of double bond in terms of atomic numbers, highest atomic number=highest priority
Repeat for other 2 groups
Z if high priority groups on same side
E is high priority groups on opposite sides
Ethene + Bromine
Step 1- electrophyllic attack on double bond
Induced dipole in Br2, d+Br joins to one C, other C becomes a carbocation, negative Br ion (heterolytic fission), Br ion bonds to cation using lone pair
Mechanism of Ethene + Bromine reaction
Electrophyllic reaction
Bromine water
Orange/brown decolourises in presence of alkene
Catalytic hydrogenation
H molecules + unsaturated alkenes–> alkane
Electrophyllic addition
Nickel/Platinum/Palladium catalyst
High temp, high pressure
Electrophyllic addition of hydrogen to ethene
d+H joins to a C, other C a carbocation, H- ion left, H- joins to carbocation
Electrophyllic addition of hydrogen bromide to ethene
d+H joins to C, carbocation, Br- ion joins to carbocation
Electrophyllic addition of HBr to propene
d+H joins to a C, carbocation, Br- joins to primary/secondary carbocation
Which carbocation is Br likely to join to?
HBr to propene reaction
Secondary carbocation is most stable, has 2 electron releasing groups either side
Secondary carbocation of HBr propene reaction forms
2-bromopropane
Alkenes + substituted alkenes
Addition polymerisation
Form polymers
