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Le Chatelier's principle?
Equilibrium will shift to oppose any change made
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Hess' Law?
Enthalpy change is independent of route taken
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Enthalpy of Combustion
Enthalpy change when 1 mole of a substance is burned in excess oxygen at s.t.p.
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Enthalpy of Formation
Enthalpy change when 1 mole of a substance is made from its constitutent elements in their standard states
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Enthalpy of reaction
Enthalpy change when molar quantities as stated in the balanced equation react together at s.t.p.
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Bond Enthalpy
Energy needed to break 1 mole of bonds in the gas state
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Catalysts:
- Are not used up in the reaction
- provide an alternative pathway
- with a lower Ea
- meaning more collisions are successful
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Heterogenous Catalysts
Catalyst and reactants are in different states
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Homogenous Catalysts
Catalyts and reactants are in the same state
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Enthalpy profile diagram:
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Using enthalpies of combustion:
- Enthalpy change = (sum of reactants) - (sum of products)
- c = r - p
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Using enthalpies of formation:
- Enthalpy change = (sum of products) - (sum of reactants)
- f = r - p
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Using Bond enthalpies:
enthalpy change = bonds broken - bonds made
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At high pressure, equilibrium will shift:
to the side with fewest moles of gas
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At low pressure, equilibrium witll shift:
the the side with most moles of gas
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At high temperature, equilbrium will shift:
in the endothermic direction
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At low temperature, equilibrium will shift:
in the exothermic direction
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Examples of heterogenous catalysis
- Iron in the Haber Process
- Pd, Pt and Rh in Catalytic converters
- Nickel in hydrogenation of alkenes
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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
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The ozone layer is maintained by:
- O2 --> 2O (radicals) needs u.v.
- O + O2 --> O3 (gives out heat)
- O3 --> O + O2 (abosorbs u.v.)
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The ozone layer is destroyed by:
- Cl. + O3 --> ClO. + O2
- ClO. + O3 --> Cl. + 2O2
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The ozone layer is destroyed by NO too:
- NO + O3 --> NO2 + O2NO2 + O3 --> NO + 2O2
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Waste polymers can be:
- Sorted and recycled
- used as feedstock for cracking
- burned to make energy
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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
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Percentage Yield:
- obtained moles x 100
- expected moles
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