CER - energetics

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CER - energetics
2011-05-25 08:33:35
Chemistry Physical enthalpy

Revision flash cards for Chains energy and resources AS Chemistry OCR A
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  1. Le Chatelier's principle?
    Equilibrium will shift to oppose any change made
  2. Hess' Law?
    Enthalpy change is independent of route taken
  3. Enthalpy of Combustion
    Enthalpy change when 1 mole of a substance is burned in excess oxygen at s.t.p.
  4. Enthalpy of Formation
    Enthalpy change when 1 mole of a substance is made from its constitutent elements in their standard states
  5. Enthalpy of reaction
    Enthalpy change when molar quantities as stated in the balanced equation react together at s.t.p.
  6. Bond Enthalpy
    Energy needed to break 1 mole of bonds in the gas state
  7. Catalysts:
    • Are not used up in the reaction
    • provide an alternative pathway
    • with a lower Ea
    • meaning more collisions are successful
  8. Heterogenous Catalysts
    Catalyst and reactants are in different states
  9. Homogenous Catalysts
    Catalyts and reactants are in the same state
  10. Enthalpy profile diagram:
  11. Using enthalpies of combustion:
    • Enthalpy change = (sum of reactants) - (sum of products)
    • c = r - p
  12. Using enthalpies of formation:
    • Enthalpy change = (sum of products) - (sum of reactants)
    • f = r - p
  13. Using Bond enthalpies:
    enthalpy change = bonds broken - bonds made
  14. At high pressure, equilibrium will shift:
    to the side with fewest moles of gas
  15. At low pressure, equilibrium witll shift:
    the the side with most moles of gas
  16. At high temperature, equilbrium will shift:
    in the endothermic direction
  17. At low temperature, equilibrium will shift:
    in the exothermic direction
  18. Examples of heterogenous catalysis
    • Iron in the Haber Process
    • Pd, Pt and Rh in Catalytic converters
    • Nickel in hydrogenation of alkenes
  19. Examples of homogenous catalysis
    • H2SO4 in dehydration of alcohols
    • H2SO4 in esterification
    • H2SO4 in addition of water to alkenes
    • Cl radical in the break down of ozone
  20. The ozone layer is maintained by:
    • O2 --> 2O (radicals) needs u.v.
    • O + O2 --> O3 (gives out heat)
    • O3 --> O + O2 (abosorbs u.v.)
  21. The ozone layer is destroyed by:
    • Cl. + O3 --> ClO. + O2
    • ClO. + O3 --> Cl. + 2O2
  22. The ozone layer is destroyed by NO too:
    • NO + O3 --> NO2 + O2
    • NO2 + O3 --> NO + 2O2
  23. Waste polymers can be:
    • Sorted and recycled
    • used as feedstock for cracking
    • burned to make energy
  24. Using catalysts is good for the environment because:
    • They are not used up
    • You can use a lower temperature
    • so save energy, and fossil fuels
    • so less CO2 is released
    • the can be very specific
    • they make less waste
  25. Percentage Yield:
    • obtained moles x 100
    • expected moles
  26. Atom economy:
    • Useful Mr x 100
    • Total Mr