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Chemistry Unit 2
Making and using alcohols
Making Ethanol: Hydration of Ethene (C2H4)
Ethanol can be manufactured industrially by the catalytic hydration of ethene
Conditions: Steam & H3PO4 Catalyst
H2C=CH2 + H2O --- (H3PO4 + Steam)- CH3CH2OH
Only 5% of ethene is converted to ethanol but the gases are recycled and passed
back through achieving a 95% conversion rate!
Fermentation
Carbohydrates are converted into ethanol and carbon dioxide
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C6H12O6 ------(yeast, 37C)- 2CH3CH2OH
Uses of Alcohols
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Alcoholic drinks
Ethanol as a fuel
Methylated spirits
Methanol as a clean burning fuel added to fuels to improve combustion

Properties Of alcohols
Alcohols have relatively high melting and boiling points
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Alcohols also have a lower volatility compared with similar length alkanes
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Primary Alcohols
-OH Group is bonded to a carbon atom with no or one alkyl groups
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C2H5OH + 3O2 ------ 2CO2 + 3H2O
Oxidation of Alcohols
Primary and Secondary alcohols can be oxidized using K2CR2O7/H2SO4
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Primary Alcohols
Distillation
Primary alcohol + [O] ---(k2cr2o7/h2so4)-- aldehyde
Reflux
Primary alcohol + [O] ---(k2cr2o7/h2so4)- Carboxylic acid
Secondary Alcohols
Secondary alcohol + [O] ----(k2cr2o7/h2so4) Ketone
Tertiary Alcohols
Cannot be oxidized
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CH3CH2COOH + CH3OH --- CH3CH2COOCH3 + H20
Esters
Are used as adhesives and solvents in the chemical industry
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Dehydration of alcohols
Conc
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Reactivity of Halogenoalkanes
Halogenoalkanes contain a polar carbon-halogen bond
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 Halogen atoms are more electronegativity
 Electron pair is attracted more towards the halogen atom than carbon
 The result is a polar bond
The electronegativity of the halogens decreases down the group, resulting in a
decrease in polarity of the carbon-halogen bond
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(NH3,OH-,H2O)
Hydrolysis of Halogenoalkanes
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When Halogenoalkanes react with hot hydroxide ions, a nucleophillic
substitution occurs
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Aqueous sodium hydroxide is usually used
Reaction carried out under reflux

A nucleophile is an electron pair donor
Nucleophillic substitution

Rate of Hydrolysis
Rates of hydrolysis can be determined using the following experiment;
The Halogenoalkane mixture is heated with aqueous silver nitrate, with ethanol
added
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The rate can be found by calculating the 1/time taken for a precipitate to form
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 Bond Enthalpy – the carbon-iodine bond is the weakest amongst the
Halogenoalkanes , so should be broken most easily and give the fastest
reaction
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Because of their low reactivity,
volatility and non- toxicity
But break down forming chlorine radicals and deplete the ozone layer
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Infrared spectroscopy
Absorption of infrared radiation causes covalent bonds to vibrate
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The amount of vibration depends on:
 Bond strength
 Bond length
 Mass of each atom involved
Modern breathalyzers use infrared spectroscopy when analyzing ethanol in
breath
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g Mg
 Three peaks means 3 isotopes
 Heights give relative abundances
 Results can be used to find Ar
Spectra tells us that :
79% is Mg-24
10% is MG-25
11% is Mg-26
Ar = (24x79) + (25x10) + (26x11) / 100 = 24
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CH4 + Br2 --------- CH3Br + HBR
Initiation
Br2 -------(UV)------ Br + Br
Propagation
Br + CH4 ---- CH3 + HBr
CH3 + Br2 --- CH3Br + Br
Termination
Br + Br -- Br2
CH3 + Br -- CH3Br
CH3 + CH3 C2H6
Further substitutions can take place, as the Bromoalkane can react with
further radicals
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In others, the products have less chemical energy than the
reactants
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Endothermic Reactions
 The enthalpy of the products is greater than the reactants
 There is a heat gain in the chemical system
 ΔH has a positive sign because heat had been gained
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CH4 + 2O2 ------ CO2 + 2H2O

ΔH= -890KJmol-1

Combustion reactions affect us all
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Respiration
Sugars like glucose are oxidized to carbon dioxide and water
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Heat provides energy that drives many reactions
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CaCO3 --- CaO + CO2 ΔH= +178KJmol-1

Enthalpy Profile Diagrams
Exothermic reactions

Endothermic reactions

Activation Energy Ea
Activation energy is the minimum energy required to start a reaction by the
breaking of bonds
Exothermic reactions
Even though the products have a lower energy than reactants, there still has to
be an input of energy to break the first bond to start the reaction
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Standard enthalpy change of formation
Of a compound is the enthalpy change that takes place when one mole of a
compound if formed from its elements in their standard states under standard
conditions
Determination of enthalpy changes
An excess of magnesium is added to 100cm of 2
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The
temperature increases from 20C to 65C
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18gkj
Density of solution 1
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Find the energy change
100cm3 of a solution has a mass of 100g
temperature change ΔT = (65-20) = +45C
Heat gained by surroundings, Q = mcΔT = 100 x 4
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Find the amount in mol that reacted
Amount in mol CuSO4 = 2
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200 mol
1000
3
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200 mol = -18810
For 1 mol (5x 18810) = -94050 = -94
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Catalysts
Increase the rate of reaction without being used up in the process
A catalyst lowers the activation energy of the reaction by providing an
alternative route for the reaction to follow
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Much of this energy comes
from burning fossil fuels
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With less energy required less fossil fuels are burnt and less carbon
dioxide is released into the atmosphere
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Enzymes as biological catalysts
Generate very specific products and operate effectively at close to room
temperatures
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 Forms pure products, no separation needed less expensive
 Conventional catalysts are usually poisonous and pose disposal problems

The Boltzmann Distribution curve
Is the distribution of energies of molecules at a particular temperature, often
shown as a graph
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 More collisions take place, the molecules have more kinetic energy so are
moving faster
 A higher proportion of molecules have an energy that is greater than the
activation energy – more successful collisions
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There
will be more successful collisions in a certain length of time the rate of reaction
will increase
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There will be more successful collisions in a certain length of time and
the rate of reaction will increase
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Le Chateliers Principle states that when a system in dynamic equilibrium is
subject to a change, the position of the equilibrium will shift to minimize the
change

The effect of a catalyst on equilibrium
A catalyst does not effect the position of the equilibrium because it speeds up
both the forward and backward reactions
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Green house gases,
Water vapor
Carbon dioxide
 Volcanic eruptions
 Respiration of animals
 Burning or decaying matter
Methane
 Emitted form production of coal
 A product of rotting waste in landfill
 Released form cattle
Gases absorb infrared radiation, this causes their bonds to vibrate
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The effect of a green house gas is dependent on its:
 Concentration
 Ability to absorb infrared radiation
Chemist role in minimizing climate change as a result of global warming by
supplying governments with evidence on global wariming
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How ozone if formed
O2 + UV ----- 2O
O + O2 ------ O3
How ozone is broken down
O3 + UV --- O2 + O
Overall
O2 + O <-- O3
Removal of ozone
O3 + 0 --- 2O2
Ozone depletion
Initiation
CFCL3 --- Cl + CFCl2
Propagation
Cl + O3 -- ClO + 02
ClO + O -- Cl + O2
Overall O3 + O -- O2

NO + O3 -- NO2 + O2
NO2 + O -- NO + O2

Catalytic Converter
2NO + 2CO -- N2 + 2CO2
a catalyst provides a surface on which the reaction takes place

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