Agriculture and Industry

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Rates and equilibria

  • Minimum amount of kinetic energy particles need to react is activation enthalpy.
  • Catalysts speed up reactions by lowering Ea by providing an alternative pathway for bonds to break and remake.  Means more particles will have enough energy to react.
  • Dynamic equilibrium occurs when the rate of forward reaction is equal to the rate of back reaction.  The concentration of reactants and products remain constant.
  • Le Chatelier's principle says: if there's a change in pressure or temperature, the POE will move to help counteract the change.
  • Catalysts have NO EFFECT on POE - they can't increase yield, only rate of reaction.
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Rates and equilibria - conditions of an industrial

Consider: rate of reaction, product yield, cost, right reaction conditions.

  • Need to make lots of product cheaply and quickly.
  • TEMP - high = faster, but expensive.
  • PRESSURE - high = faster, expensive and DANGEROUS (reaction vessels must be made of stron material and incorporate safety systems = expensive)
  • CATALYSTS - can be expensive, but will make reaction faster at lower temp.  DON'T GET USED UP.
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Haber process (don't need to know)

POE affects how economical a reaction is.

N2(g) + 3H2(g)  <----> 2NH3(g)  Enthalpy change = -92kJmol^-1

  • Carried out at 400C and 200atm.
  • High pressure moves POE to right as fewer molecules, so increasing yield.  Also increases rate of reaction.
  • Higher temp makes reaction go faster, but lowers product yield as POE would shift to left.
  • 400C is compromise - greater yield at lower temp, but too slow to be economical.
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Equilibrium constants

  • Kc is equilibrium constant.
  • Need to know MOLAR CONCENTRATION of each substance at equilibrium.
  • Kc value only true for that particular temp.
  • Equation:



  • With gases, can use PARTIAL PRESSURES instead of concentrations.
  • Total pressure of a gas mixture is the sum of all partial pressures of individual gases.
  • Partial pressure of A = (number of moles of A/total number of moles of gas) * total pressure
  • If number of moles of gas increases, so does its partial pressure.
  • Only changes in TEMPERATURE causes Kc and Kp to change.
  • Catalysts don't have an effect, as they affect forward and back reactions equally, so no overall change to equilibrium.
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Nitrogen chemistry

  • Occurs naturally as diatomic molecule and has triple bond.
  • N2 very unreactive as triple bond difficult to break.
  • In ammonia, N forms covalent bonds with H leaving a LP.
  • NH3 forms H-bonds = very soluble in water.
  • LP means can form dative covalent bonds - LIGAND.
  • LP also means acts as a BASE - NH3 + H+ forms NH4+.
  • 3 oxides need to learn about:
    • NO - nitrogen monoxide - colourless gas.
    • N2O - dinitrogen monoxide - colourless gas, sweet smell.
    • NO2 - nitrogen dioxide - brown gas, sharp odour, toxic.
  • The purpose of the nitrogen cycle is to convert nitrogen into more accessible forms.  It converts nitrogen through its different oxidation states.
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Chemical industry

  • Industrial chemical production impacts on the environment by:
    • Using raw materials and energy
    • releasing waste products
  • % ATOM ECONOMY = (mass of desired product/total mass of products) x 100
  • % YIELD  = (actual product yield/theoretical yield) x 100
  • Costs involved running a chemical plant
    • Raw materials - cheap, widely available ones best.
    • Lots of E needed for high temp and pressure and to transport chemicals.
    • Fixed costs - staff wages, rent, insurance, bills,
    • Disposal costs - unwanted products disposed of safely.
  • Risks of producing a chemical
    • Some chemicals highly flammable - must be stored and handled correctly.
    • Some chemicals harmful to health - Cl toxic if inhaled - irritate eyes and lungs.  Spill during transportation could expose danger to public.
    • Some chemicals damage environment - SO2 contributed to acid rain.
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Chemistry industry can improve food production.  There are three ways:


  • Provides crops with nutrients = increased crop yield.
  • May result in leaching, therefore eutrophication.
  • Nitrate (V) ions get into drinking water - health risks to children.


  • Each crop has optimum soil pH.
  • Too acidic = poor plant growth, so add limestone to neutralise acid.


  • Pesticides kill pests, which reduce crop yield.
  • Pesticides may accumulate in food chain and build up being harmful to birds etc.
  • Kill non-target organisms, which may have been beneficial to crop.
  • May be washed from soil, end up in drinking water.
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