Calorimetry

Calorimetry

method for measuring energy released by chemical reactions
Q=mcdeltaT
1. Q=energy in joules
2. m=mass of water in grams
3. c=specific heat capacity of water(4.2 J/g degrees celsius)
4. delta T=change in temp
errors
1. lot of heat loss to the surroundings
2. not all of the food/fuel burns
3. water should be stirred
4. some energy heat the container
Energy level diagrams
1. supply energy to break bonds
2. energy released when making bonds
3. exothermic - energy given out (high energy level to low level energy
  1. energy released from forming new bonds is greater than energy needed to break bonds
  2. eg combustion/neutralisation
  3. deltaH is negative
4. activation energy
  1. catalyst can provide a different pathway that has a lower activation energy
  2. the minimum amount of energy that colliding reactant particles must have for a reaction to occur
5. endothermic-energy taken in (low energy level to high energy level)
  1. energy needed to break bonds is greater than the energy released from forming new bonds
  2. deltaH is positive
  3. thermal decomposition
6. Bond energies
  1. the amount of energy needed to break a particular chemical bond
  2. measured in KJ/mole
  3. 1) calculate total amount of energy needed to break all the bonds in reactants
    1. 2) calculate total amount of energy released in making all the bonds in products
      1. 3) overall energy change = energy in - energy out
  4. exothermic reaction, the energy needed to break existing bonds is less than the energy released from forming new bonds
  5. endothermic reactions , the energy needed to break existing bonds is more than the energy released from forming new bonds
  6. Hydrogen power
    1. when hydrogen burns in air the only product is water
      1. does not contain carbon - so hydrogen burns with an invisible flame
    2. alternative fuel because of the concern that burning fossil fuels produce greenhouse gases and is accererating the climate change
      1. no emissions of smoke or carbon dioxide when burning hydrogen
    3. drawback - must be liquified or pressurised so it can occupy a smaller volume
      1. in terms of energy density / gram --- hydrogen releases far more energy than other fuels
        but at room temp it is a gas so energy density is far lower than that of petrol an other liquid fuels
        hydrogen fuelled vechiles would need huge tanks if they stored hydrogen as a gas at atmospheric pressure
    4. fuel cells produce electricity by the reaction of hydrogen with oxygen
      1. water only waste product
      2. hydrogen and oxygen do not react together directly in a fuel cell
        kept apart by partially permeable membrane that only allows hydrogen ions
      3. fuel cells very efficient in producing electricity as long as they are supplied with fuel and oxygen
      4. hydrogen not truly clean fuel as it is made from fossil fuels directly or indirectly using electricitty......so as a fuel it uses non-renewable resources and produces CO2 emissions
        investigation of modyifying photosynthesis so that algae produce hydrogen

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