AS Chemistry AQA Unit 2 Flashcards
Enthalpy change
Heat energy transferred in a reaction at constant pressure
Le Chatelier’s principle
If a system in equilibrium is disturbed, the point of equilibrium will shift to counteract the change
Mean bond enthalpy
Average value for a bond enthalpy over the range of compounds it is found in
Enthalpy change of a reaction
Total energy absorbed - Total energy released
Standard enthalpy of reaction
The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, with all reactants and products in their standard states and under standard conditions
Standard enthalpy of formation
The enthalpy change when one mole of a product is formed from its elements, under standard conditions with all reactants and products in their standard states
Standard enthalpy of combustion
The enthalpy change when one mole of a substance is completely burned in excess oxygen, under standard conditions, with all reactants and products in their standard states
Measuring enthalpy change
q = mcΔt
q= heat change, m=mass of solution heated, c=specific heat capacity of water (4.18) Δt= change in temp
standard enthalpy change = q/n
Activation energy
The energy required for a reaction to start
Catalyst
Increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy
Steam Hydration of ethene
C2H4 + H2O <–> C2H5OH
Conditions for steam hydration of ethene
6000-7000kPa (60-70 atm)
Temperature of 300 degrees
SOLID phosphoric acid catalyst
Methanol production
2H2 + CO <—> CH3OH
Conditions for methanol production
5000-10000 kPa (50-100 atm)
250 degrees
Mixture of catalysts: copper, zinc oxide, aluminium oxide
Uses of ethanol
Alcoholic beverages
Fuel
Uses of methanol
Fuel
Mainly used to produce other chemicals
Redox reaction
Reaction in which oxidation and reduction occurs simultaneously
Oxidation state of oxygen
-2 except for peroxides, where it is -1
Oxidation state of hydrogen
+1 except for in metal hydrides, where it is -1
Half equations
Electrons and ions, and element
Show reduction or oxidation
Halogen boiling point trend
Increase down group
Halogen electronegativity trend
Decrease down group (shielding, atomic radius)
Reaction: Bromine water and potassium iodide
Iodine is displaced; brown solution
Reaction: Chlorine water and potassium bromide
Bromine is displaced; orange solution
Making bleach
2NaOH + Cl2 —> NaClO + NaCl + H2O
Sodium hydroxide + Chlorine= Sodium chlorate(l) + Sodium chloride + water
Disproportionation
The oxidation and reduction of the same element in a redox reaction
Reaction: Chlorine and water
Cl2 + H2O <—> HClO + HCl
Risks of chlorine
Irritate respiratory system
Chemical burns
Chlorinated hydrocarbons are carcinogenic
Equation: Conc. sulphuric acid and sodium chloride/fluoride
H2SO4 + NaCl —> NaHSO4 + HCl
Steamy fumes of HCl as it meets moisture in air
HCl or HF cannot reduce sulfuric acid; reaction ends
Equation: Conc. sulphuric acid and sodium bromide
H2SO4 + NaBr —> NaHSO4 + HBr
Steamy fumes of HBr
HBr is stronger reducing agent than HCl or HF; reduces sulfuric acid
2HBr + H2SO4 —> SO2 + Br2 + 2H2O
Equation: Conc. sulfuric acid and sodium iodide
H2SO4 + NaI ---> NaHSO4 + HI Steamy fumes of HI HI is strong reducing agent; reduces sulfuric acid 2HI + H2SO4 ---> SO2 + I2 + 2H2O HI continues to reduce SO2 6HI + SO2 ---> H2S + 2H2O + 3I2
Observations: Conc sulfuric acid and sodium chloride/fluoride
Steamy fumes of HCl or HF
Observations: conc sulfuric acid and sodium bromide
Steamy fumes of HBr, choking fumes of SO2, orange fumes of Br2
Observations: conc sulfuric acid and sodium iodide
Steamy fumes of HI, choking fumes of SO2, purple fumes of I2, bad egg smell of H2S, black solid (iodine)
Test for halides
Silver Nitrate test;
Add nitric acid to remove carbonate ions (ions that interfere)
Add silver nitrate
White ppt indicates chloride, cream ppt indicates bromide, yellow ppt indicates iodide
Dissolves in dilute ammonia=chloride, dissolves in conc ammonia=bromide, doesn’t dissolve in conc ammonia=iodide
Melting point of group 2 metals
Decrease down group; blip at magnesium bc crystal structure
Group 2 metal reactions with water
Form metal hydroxide and hydrogen
Group 2 hydroxide solubility
solubility increases down group
Group 2 sulphate solubility
solubility decreases down group
Test for sulfate ions
Barium ions, e.g. barium chloride (acidified with HCl)
Test for hydroxide ions
Magnesium ions, e.g. magnesium chloride
Slaked lime
Ca(OH)2 calcium hydroxide used to neutralise acidic soil
Extracting metals from sulfide ores
- Turn into oxide; roast in air
2. Reduce oxide
Roasting
Heating in plenty of air
Reducing iron(lll) oxide
Blast furnace, over 700 degrees
Carbon or carbon monoxide reducing agent
2Fe2O3 + 3C —> 4Fe + 3CO2
Fe2O3 + 3CO —> 2Fe + 3CO2
Reducing manganese(lV) oxide
Blast furnace, 1200 degrees
Carbon or carbon monoxide
MnO2 + C —> Mn + CO2
MnO2 + 2CO —> Mn + 2CO2
Reducing copper carbonate
heat with carbon, or decompose into oxide and reduce with carbon
Malachite
contains CuCO3, iron ore
Extracting tungsten
Hydrogen
Furnace, above 700 degrees
Extracting aluminium
Electrolysis; remove impurities, bauxite dissolved in molten cryolite, pure aluminium collects as molten metal
Bauxite
Al2O3, aluminium ore
Cryolite
Na3AlF6 reduces aluminium melting point
Extracting titanium
Carbon and chlorine to form titanium chloride
React with more reactive metal eg sodium to get pure metal
Evaluation recycling metals
+ ores are a finite resource - saves raw materials; saves energy; reduces landfill waste; mining damages landscape
-collecting and sorting metals is expensive and hard; purity of metal varies; recycling may not produce consistent supply
Using scrap iron
Dissolve copper ores in acidified water, scrap iron added. Iron dissolves and reduces copper ions; copper precipitate forms
Synthesis of chloroalkanes
free radical substitution; react alkane with halogen with UV
Ozone layer
O2 breaks down into O radicals under UV
O2 + O’ —> O3
ABSORBS UV IN THIS WAY
Ozone breakdown by CFCs
CCl3F —> CCl2F’ + Cl’
Cl’ + O3 —> ClO’ + O2
ClO’ + O3 —> 2O2 + Cl’
OVERALL: 2O3 —> 3O2
CFC uses
propellant in aerosols, coolant gas in fridges
Nucleophile
Electron pair donor
Electrophile
Electron pair acceptors
Nucleophilic substitution
Nucleophile attacks polar molecule, replaces it
Examples of nucleophiles
:NH3, :CN-. :OH-
Synthesising amines
Warm haloalkane with ethanolic ammonia (ammonia dissolved in ethanol)
Ammonia swaps with halogen; NUCLEOPHILIC SUBSTITUTION
Synthesising nitriles
Warm haloalkane with ethanolic potassium cyanide
NUCLEOPHILIC SUBSTITUTION
Hydrolysis of haloalkanes
Warm aqueous sodium hydroxide and haloalkane
Nucleophilic sub vs elimination
React haloalkane with water, under reflux = nucleophilic sub, not much elimination
React haloalkane with ethanol under reflux= elimination
Test for unsaturation
Shake with bromine water- orange to colourless means unsaturation
Carbocation
Organic ion containing positively charged carbon atom
Hydration of alkenes
React alkene with water, with cold concentrated sulfuric acid
- alkene and sulfuric acid
- add cold water and warm; hydrolysed to ethanol
Synthesis of bromoalkanes
ELECTROPHILIC ADDICTION
C2H4 + HBr —> C2H5Br
Unsymmetrical alkanes
Br bonds to most stable carbocation (tertiary most stable, primary least stable)
Polymerisation
n (H2C=CH2) —> n(-CH2-CH2-)
Polyethene uses
Soft flexible plastic, plastic bags and squeezy bottles
Polypropene uses
Tough, strong plastic. Bottle crates, rope.
Production of ethanol by fermentation
30-40 degrees yeast anaerobic conditions C6H12O6 ---> 2C2H5OH + 2CO2 around 15% alcohol, yeast dies Fraction distillation increases conc of alcohol
Dehydration of ethanol
react with conc sulfuric acid (or phosphoric acid) REFLUX
C2H5OH + H2SO4 —> C2H5OSO2OH + H2O
C2H5OSO2OH —> C2H4 + H2SO4
Oxidation of alcohols
Acidified potassium dichromate, orange to green
Primary: distilling: Aldehyde reflux: Carboxylic acid
Secondary: reflux: ketone
Tertiary: not oxidised
Tollens reagent
Silver mirror with aldehyde, none with ketone
Reduced to silver with aldehyde
Fehlings solution
Blue to brick red with aldehyde, not ketone
