2009 Chemical, Energy and Resources Jun Flashcards
State two factors which affect the contribution of greenhouses to global warming
• Ability to absorb infrared radiation
• Residence time
• Atmospheric concentration
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Define enthalpy change of combustion
• The enthalpy change for the complete combustion
• of 1 mol (of a substance)
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What is meant by the term atom economy
• (Sum of) the molecular masses of the desired product ÷
sum of molecular masses of all products × 100
CO + 2H2 -> CH3OH ∆H = –91 kJ mol–1
High pressures and low temperatures would give the maximum equilibrium yield of methanol
- High pressure as fewer moles (of gas) on right-hand side
* Low temperature as (forward) reaction is exothermic
Why the actual conditions for this will not be high pressure and low temperature
- Too expensive to use a high pressure
* Too slow to use a low temperature
Chlorine radicals catalyse some reactions. Choose a reaction you have studied that is catalysed by chlorine radicals
- Cl + O3 -> ClO + O2
- ClO + O -> Cl + O2
- Overall: O3 + O -> 2O2
Suggest two ways in which the use of catalysts helps chemical companies to make their processes more sustainable
- Catalyst not used up in reaction
- Reactions take place at lower temperatures
- Different reactions can be used with better atom economy
- Catalysts or enzymes can generate specific products
Explain why 1-iodopropane hydroylsed faster than 1-bromopropane
- C–I bonds broken more easily
* C–I bonds are weaker
Why is there still concern about ozone depletion
- CFCs take many years to reach the ozone layer OR long residence time
- CFCs are still being used
- there are other ozone depleting substances
Outline two ways in which the waste polymers are processed usefully
- Separation into types and recycling
- Combustion for energy generation
- Used for cracking
