Unit 3 - Chemical Reactions

The UK Chemical Indusrty
1. Main Categories
  1. pharmaceuticals
  2. petrochemicals & polymers
  3. paints & pigments
  4. speciality chemicals
  5. inorganics & fertilisers
2. Stages
  1. 1) Raw Materials: fossil fuels, metallic ores, minerals, air, water
  2. 2) Feedstock: a reactant from which other chemicals are extracted or synthesised
  3. 3) Reactor: feedstock converted into product, batch or continuous
  4. 4) Separation: evaporation, distillation, absorption, condensing, precipitation, filtration, drying
3. Location
  1. historical/practical: transport routes, existing industries - ease of access to feedstocks
  2. safety/environmental: release of by-products into atmosphere/water systems
4. Process
  1. Batch
    1. Pros: variety of products, plants less expensive to build, can be used for slow reactions, reactants can be in any state
    2. Cons: labour intensive, lost production when filling/emptying reactors, lost production when changing from 1 product to another because reactors often need to be cleaned
    3. small quantities of chemicals, pharmaceuticals, dye-stuffs, pesticides
  2. Continuous
    1. single products, operate year round, petrochemicals, ammonia, sulphuric acid
    2. Pros: less labour intensive, quality control of products more easily ensured, continuous operation makes for economic efficiency because shut downs are rare
    3. Cons: specific feedstock, plants expensive to build, solid reactants need to be in a fine powder because larger particles black pipes
5. Stages in Manufacture
  1. 1) Research/Development: identification of new product, development of suitable process
  2. 2) Pilot Study: scaled down version of plant, product quality, health hazards & costs are evaluated
  3. 3) Scaling Up: planning & development of a full scale plant
  4. 4) Production: new product manufactured
  5. 5) Review: processes are reviewed, modifications made, attempts made to reduce costs, hazards to health, safety & enviroment
6. Costs
  1. Capital: initial cost of building plant, research, development & associated structure
  2. Fixed: salaries, maintenance(depreciation), sale expenses
  3. Variable: cost of raw materials, distribution of product, energy costs & waste product treatment/disposal
Chemical Reactions
1. Hess' Law
  1. the enthalpy change is independent of the route taken
  2. the enthalpy of the direct route is the same as the indirect route
  3. /\H = /\H2 + /\H3
2. Enthalpy
  1. combustion: 1 mole burns completely in oxygen
  2. solution: 1 mole of a substance dissolves in water
  3. neutralisation: acid is neutralised to form 1 mole of water
Equlibrium
1. Dynamic Equilibirium
  1. concentrations of reactants & products are constant
  2. rate of forward & backward reaction are equal
2. Concentration
  1. Addition of reactant
    1. increase in concentration of products
      1. rate of forward reaction increases
        moves to the right
  2. Addition of product
    1. increase in concentration of reactants
      1. rate of backwards reaction increases
        moves to the left
  3. Removal of product
    1. increase in concentration of products
      1. rate of forward reaction increases
        moves to the right
  4. alkalis react with H+ ions to make water - removing them from the equilibrium, acids react with OH- ions
3. Other fatcors
  1. Temperature
    1. decrease in temp. favours exothermic
      1. increase in temp. favours endothermic
  2. Pressure
    1. increase in pressure favours side with less gas molecules
    2. decrease in pressure favours side with more gas molecules
  3. Catalysts
    1. increase the rate of both reaction
      1. does not effect the position of equilibrium but means it is achieved more quickly
4. Haber Process
  1. ammonia produced by the reaction of nitrogen & hydrogen in the presence of an iron catalyst
  2. Conditions for Max. Yield
    1. 1) after leaving the reaction chamber, the gaseous mixture is passed through a condenser, liquid ammonia is constantly removed, reducing the rate of the backward reaction
      1. 2) unreacted hydrogen & ammonia gases are recycled, increasing the rate of the forward reaction
        3) because the forward reaction is exothermic & has fewer gas molecules present, the pressure will be low. high pressures & low temperatures will produce the greatest yield
  3. Chemical Plant Conditions
    1. higher temp. than ideal because the reaction takes too long at low temp.s, the cost of running a plant at high pressure is is high, so the pressure is lower than ideal
Acids & Bases
1. pH is a measure of H+ concentration in a solution
2. Water Equilibrium
  1. water partially dissociates to form H+ & OH- ions
    1. poor conductor of electricity due to small no. of ions at equilibrium
      1. concentration of [H+] & [OH-] is equal (1 X 10^-7 mol^-1)
        ionic product of water (Kw) = the multiple of the concentration of [H+] & [OH-] ions in 1 mole of watrer
        Kw = [H+] X [OH-} = (1 X 10^-7 mol l^1) X (1 X 10^-7 mol l^-1) =1 X 10^-14 mol^2 l^-2
3. Equilibrium in acids & alkalis
  1. must all add up to 1 X 10^-14
  2. acid is a H+ donor , results in an increase in H+ ions & a decrease in OH- ions and an alkali does the opposite
  3. pH 1 = 1 X 10^-1 H+ ions (0.1 mol l^-1) & 1 X 10^-13 OH- ions (0.0000000000000001 mol l^-1)
4. Strong & Weak Acids
  1. Strong: fully dissociated in dilute solution (ionised) due to polar covalent nature of acid molecule.
    1. hydrochloric, sulphuric, nitric
  2. Weak: partially dissociated in a dilute solution
    1. ethanoic, citric, carboxylic
  3. pH: strong acids have a lower pH because they have a greater concentration of H+ ions
  4. Conductivity: increases with the number of ions present, therefore strong acids have a higher conductivity
  5. Reactions: strong acids fully dissociate and therefore have excess H+ ions which react. weak acids don't have H+ ions in excess but as the H+ ions react the equilibrium position changes & more H+ ions are released to react. so strong acids react faster but both acids give the same volume & mass of product
5. All the concepts of strong & weak acids are the same for bases but with OH- ions instead of H+ ions
6. Salt Solutions
  1. strong acid + strong base = neutral solution
    1. weak acid + strong base = alkaline solution
      1. strong acid + weak base = acidic solution
  2. when an acidic salt dissolves in water it forms an acidic solution
    1. the weak ion in the salt reacts with the OH- ions - taking them out of the water equilibrium mixture
      1. these ions must be replaced, so water molecules break down to replace the OH- ions & produce H+ ions at the same time
        this results inn excess H+ ions and an acidic solution is formed
        This is the same as for alkaline salts but the other way around
  3. Soap is formed from the hydrolysis of fats & oils
    1. fats & oils are made from glycerol & fatty acids
      1. fatty acids are carboxylic acids which are weak
        fats & oils are boiled in sodium hydroxide (strong base) to produce soap
        therefore, soaps are salts formed from a weak acid & a strong base - soaps dissolve in water to form an alkaline solution
Redox Reactions
1. during redox reactions, one species is oxidised &n another is reduced
  1. displacement reactions are an example of redox reactons
2. Writing Redox
  1. balance electrons
    1. combine
3. Oxidation Is Loss Reduction Is Gain
4. Agents
  1. oxidising agents accept electrons - it is reduced
  2. reducing agents donate electrons - it is oxidised
5. oxy anions
  1. negative ions which contain oxygen combined with another element
  2. 1) balance the non-oxygen element
    1. 2) balance oxygen with water molecules
      1. 3) balance hydrogen in water molecules by adding H+ ions
        4) balance the charges on either side by adding electrons
6. Redox Titrations
  1. the concentration of a reactant can be calculated by the results of a redox titration
  2. 1) identify the 2 substances involved in the calculation & work out the mole ratio
    1. 2) place all the information from the passage under appropriate headings (volume etc.)
      1. 3) calculate the no. of moles from the species for which you know all the data
        4) using mole ration, calculate the no. of moles for the other substance
        5) calculate the concentration of the substance you worked out the no. of moles for in step 4
  3. this equation can also be used
    1. C1V1/n1 = C2 V2/n1
7. Electrolysis
  1. when a current of electricity is passed through an ionic solution, the compound is broken down to produce its elements e.g. the electrolysis of CuCl(aq) produces copper & chlorine
  2. Electrodes
    1. negative
      1. reduction takes place
        a solid is produced
    2. positive
      1. oxidation takes place
        gas produced
  3. Quantitive Electrolysis
    1. Faraday's Number - Faraday's Law states that the no. of moles of a substance produced at an electrode during electrolysis is proportional to the no. of moles of electrons transferred to the electrode
      1. the amount of electrical charge carried by 1 mole of electrons is 96500C (F)
        e.g. Na+(aq) + e- = Na(s)
        1 mole of electrons produces 1 mole of sodium
        1 X 96500C
      2. the no. of coulombs of charge going through a solution or melt can be calculated using the following formula: Q (coulombs) = I (current in amps) X t (time in seconds)
    2. calculating mass/volume produced
      1. 1) calculate the no. of coulombs of charge
        2) write the ion electron equation & identify the mole ratio (electrons to solid)
        3) using the mole ration, calculate the mass of the solid e.g. mole ratio of 3:1 would mean 1 X GFM
        if mole ratio is 3:1, (3 X 96500) = (1 X GFM)
        (mole ratio 3:1) therefore, Q X (1 XGFM) / (3 X 96500) = mass of solid
    3. calculating time taken to produce a known mass/volume
      1. 1) write ion electron equation & determine mole ratio (between reactant & electrons)
        2) use mole ratio to determine Q
        3) rearrange Q = It into t = Q/I
    4. calculating what current is required to produce a known mass/volume
      1. 1) write ion electron equation & determine mole ratio
        2) use mole ratio to determine the no. of coulombs of charge
        3) rearrange Q = It to I = Q/t
Nuclear Chemistry
1. Types of Radiation
  1. isotopes - atoms of the same element with differing mass no.'s & therefore different no.'s of neutrons
  2. Radioisotopes - unstable nuclei which emit radiation & energy to form stable nuclei
    1. stability depends on proton:neutron ratio
      1. stable nuclei (lighter elements) contain a roughly equal no. of neutrons & protons
        as the nuclei of the elements increase in size, the ratio of neutrons:protons increases
        nuclei of heavier atoms are therefore unstable, most of the isotopes of elements beyond element 83 are unstable
        radioactivity is the result of unstable nuclei rearranging to from stable nuclei
  3. Background Radiation
    1. the world contains many radioactive sources - background radiation
      1. this ranges from, rocks, building materials, cosmic rays, medical applications, disposal of nuclear waste, smoke detectors
  4. Alpha
    1. helium atom (^4v2He), can't get through paper
      1. positive charge, strongly deflected by a positive charge
  5. Beta
    1. produced when a neutron breaks down to produce a proton & an electron, the proton stays in the nucleus, the electron (^-1v0e) (beta particle) is emitted
      1. can't get through aluminium
        negative charge, slightly deflected by a positive charge
  6. Gamma
    1. high energy electromagnetic wave
      1. can't get through lead
        no charge, therefore no deflection
2. Nuclear Equations
  1. Alpha
    1. mass number decreases by 4
      1. atomic number decreases by 2
  2. Beta
    1. atomic number decreases by one
3. Half - lives
  1. the half-life of a radioisotope is the time taken for the activity or mass of a sample to halve
    1. the symbol given to half-life is t1/2
      1. the decay of individual nuclei within a radioisotope is random, the decay curves for all isotopes all follow the same pattern
  2. not effected by temperature or pressure or chemical states
  3. different radioisotopes of the same element have different half-lives e.g. lead-212 has a half-life of 10.6 while lead-214 has a half-life of 26.8 minutes
  4. half-life & radiation intensity are different, the half-life is for a particular isotope & the intensity for the mass or concentration of a isotope present
4. Artificial radioisotopes - stable nuclei can be made unstable by bombarding them with particles such as protons, neutrons or alpha particles. these radioisotopes usually have short half-lives
5. Uses
  1. medicine
    1. cobalt-60, cancer treatment
      1. if used in the body, radioisotopes should have short half-lives & be beta or gamma because alpha particles cause cellular damage
  2. scientific research
    1. carbon dating
      1. during photosynthesis, plants take in carbon-14 s part of their CO2, when a plant dies there is no more uptake of CO2 & therefore the carbon-14 in the plant decays, the proportion of carbon-14 to carbon-12 changes so the age can be measured by this, the half-life of carbon-14 is 5730yrs
  3. industry
    1. measuring thickness of thin metals (alpha)
6. Fission: nuclei of heavy element bombarded with neutrons causes it to split into lighter nuclei, neutrons, energy, 2 neutrons released bombard other nuclei - self-sustaining (chain reaction
  1. Fusion: heavy nuclei are formed by the fusing of 2 light nuclei - takes place in stars

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