Agriculture and Industry

atom economy = (Mr useful product / total Mr reactants)  x 100

Rearrangement and Addition reactions also have an atom economy of 100%

CH3CH2CH2CH2CH2CH3 --------> CH3C(CH3)2CH2CH3

 Mr = 86.0                                      Mr = 86.0                  =100% atom economy

CH2CH2        +       H20       --------->      CH3CH2OH

Mr = 28.0     Mr = 18.0                      Mr = 46.0                =100% atom economy

Substitution and Elimination reactions have and atom economy of less than 100% 

The principles of green chemistry are:

• minimise waste
• reduce feedstock consumption
• reduce energy consumption. 

The properties of materials are determined by:

• The types of particles in the material - e.g. atoms, ions or molecules
• The bonding in the material - e.g. covalent, ionic, metallic or intermolecular bonds
• The structure present in the material - e.g. giant lattice, molecular or macromolecular

Trends in properties

• Giant lattice structures generally have high - very high meting and boiling points. 
• Covalent molecular structures usually have low - moderate meting and boiling points.
• Giant lattice structures are usually insoluble in non-polar solvents
• Covalent molecular structures are mostly soluble in non-polar solvents

The law of equilibria states:

Kc  =  [C]^c[D]^d / [A]^a[B]^b   (Products divided by the reactants)

The Kc is the equilibrium constant for the reaction at a specified temperature. 

Kc is a measure of how far a reaction proceeds. If an equilibrium mixture is composed largely of reactants, then the value of Kc is small, and vice versa.  

                                            Exothermic reactions          Endothermic reactions

Temperature increases      Value of Kc decreases      Value of Kc increases

Temperature decreases     Value of Kc increases       Value of Kc decreases 

Manufacture of ammonia (Haber Process)

The raw materials are air and natural gas, from these, a feedstock of nitrogen and hydrogen, ratio 1:3, is made.

N2 (g) + 3H2 <------> 2NH3 (g)    

The usual conditions are:

• iron catalyst
• temp 450 degrees Celsius
• 200 atm pressure 

Increasing the temperature speeds up the rate of the equilibrium, but decreases the yield. The position of the equilibrium moves to the left (exothermic reaction)

Increasing the pressure increases yield (position of equilibrium moves to side with fewer moles) and the rate. It is expensive (capital costs and electricity costs). Using a catalyst speeds up the rate at which equilibrium is achieved.

Nitrogen gas consists of diatomic molecules, which are very unreactive because of the extremely high activation energy needed to start breaking bonds. 

Nitrogen species    Formula   Oxidation state     Action producing the species 

Nitrogen gas            N2 (g)           0         Denitrifying bacteria in the soil

Nitrate(v) ion           NO3- (aq)   +5         Nitrifying bacteria in the soil

Nitrate(iii) ion          NO2-  (aq)   +3        Nitrifying bacteria in the soil

Ammonium ion        NH4+  (aq)   -3         Root nodules in legumes, bacteria and microorganisms                                                                                       in soil

Dinitrogen(i) oxide   N2O (g)     +1        Denitrifying bacteria in soil 

Nitrogen(ii) oxide     NO (g)      +2        Car engines, thunderstorms, denitrifying bacteria in soil

Nitrogen(iv) oxide    NO2 (g)     +2        Oxidation of NO in the atmosphere