C3 - Chemical Economics

C3 - Chemical Economics

1. rates of reaction (1)

   • how long it takes for a product to form (react)
     • fast at the start and slows to the end
   • it can be worked out from the gradient of a graph
     • slope of gradient = y/x
     • the limiting reaction is the reaction NOT in excess that gets used by but the end of the reaction
       • the amount of product formed in a reaction is directly proportional to the amount of the limiting reactant used
         • reaction occurs when particles collide together. if the number of reacting perticles of one reactant is limited, the number of collisions is limited

2. rates of reaction (2)

   • the higher the number of collisions that take place, the faster the reaction
     • it can increase by increasing the concentration: raising the temp or the pressure
       • particles become more crowded -> more collisions
         • kinetic energy -> move around more quickly
     • collision frequency: this describes the number of successful collisions between reacting particles each second

3. rate of reaction (3)

   • explosions and surface area
     • combustible powders can cause explosions
       • breaking up a block into smaller pieces increases the surface area
   • catalysts
     • a catalysts speeds up a reaction. it doesn't change at the end of a reaction

4. reacting masses

   • relative formula mass
     • relative atomic mass(A) in the periodic table, the elements all have two numbers. the bigger one is the relative atomic mass (on top)
     • relative formula mass(M) is all the relative atomic masses added together
   • conservation of mass: during a reaction there are the same number and types of atoms on each side. becuase of this we say the mass is conserved

5. percentage yield and atom economy

   • percentage yield = (actual yield/predicted yield) x 100
   • the percentage yield tells you about the overall success of an experiment. it compares what you think you should get with what you actually get
   • industrial processes need a high % yield so that they: -reduce waste of reactants, which is costly and wasteful -reduce their costs
     • they want a high atom economy to make the process more sustainable by making better use of reactants, conserving raw materials and avoiding need to get ride of waste products
   • atom economy = (M of desired products/sum of M of all products) x 100
   • atom economy is the % of reactants changed to useful products

6. energy

   • bonds BREAKING is an ENDOTHERMIC process
   • bonds MAKING is an EXOTHERMIC process
   • energy is needed to break reactants into separate atoms
     • atoms join to form new bonds, releasing energy
       • if more energy is released then needed, the reaction is exothermic
         • if more energy is needed then released, the reaction is endothermic
   • energy transferred by a fuel
     • energy transferred (in J) = mass x specific heat capacity x temp change
     • energy in a gram of fuel = energy released (in J)/ mass of fuel burnt (in g)

7. batch or continuous

   • disadvantage
     • continuous
       • inefficientif not in constant use
         • there is a high initial building and set-up costs for the chemical platns
     • batch
       • each batch has to be supervised so labour costs rise
         • time is needed for cleaning if product line if changed
           • it is inefficient if product is not used all the time.
   • advantages
     • continuous
       • makes large amounts of products 24/7
         • takes place in large chemical plants with good transport links
           • plants are automated so have minimum labour costs, making product cheaper
             • less energy to maintain
     • batch
       • makes a fix amount
         • allows batches to be stored until needed
           • easy to change production to a different product
             • can be sold within a given time ('sell by' date)

8. allotropes of carbon and nanochemistry

   • allotropes are just different structural forms of the same element in the same physical state