Agriculture and Industry

• 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.

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.

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.

• 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.

• 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.
• LEARN NITROGEN REDOX REACTIONS.

• 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.

Chemistry industry can improve food production.  There are three ways:

1. FERTILISTING THE SOIL

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

2. ACID NEUTRALISATION

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

3. KILLING PESTS

• 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.