AQA Radical reactions of Alkanes and Ozone Depletion
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| What is the effect of Infra Red radiation on a molecule? | BONDS vibrate MORE
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| What is the effect of UltraViolet Radiation on a bond? | BONDS split homolytically, producing 2 radicals
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| Describe in detail the effect of increased concentration of CO2 in the atmosphere? | C=O BONDS absorb IR energy; so the bonds vibrate MORE; the kinetic energy is passed on to colliding molecules; increased concentration of CO2 means more IR absorbed and ...more kinetic energy passed on; overall effect is warming up of the atmosphere
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| Explain why CFC are not split until the Stratosphere, but not in the troposphere | the UV radiation in the troposphere has not got a frequency HIGH enough to split the bonds
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| CHALLENGE: Explain why CFC are damaging the Ozone layer but Bromo compounds are not | C-Br BOND is weaker/lower bond enthalpy so can broken by low energy radiation/low frequency UV which exists in the troposphere; C-Cl and C-F BONDS require high energy UV which is only found in the stratosphere
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| Describe why CFC are damaging the ozone layer | In the stratosphere, C-Cl BONDS absorb HIGH ENERGY UV radiation; the BOND splits homolytically to form Cl radicals; Cl radicals combine with Ozone to form Oxygen MOLECULE and oxygen RADICAL; O* combines wi; Cl* are regenerated=act as catalyst
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| Define propagation step | When a radical reacts with a molecule forms a different radical
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| Define Termination step | When two radical combine together to form a molecule
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| Define a radical | A species (atom or molecule) with an unpaired electron
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| Which bond has the highest bond enthalpy? C-Br or C-Cl? | C-Cl
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| Write the equation to show the homolytic fission of BromoTriChloroMethane | F3C-Br --> F3C* + *Br
Show ALL bonds; the bond that breaks first here is the C-Br as it is the weakest
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| What TYPE of particles are formed by heterolytic fission? | ions
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| What TYPE of particles are formed by homolytic fission? | radicals
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| State uses of CFCs and explain the uses by referring to their property | solvent, because they have low boiling point and refrigerant because they are non-flammable and non-toxic
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| What is homolytic fission? | When a covalent bond splits with each atom taking one electron; forming thus two radicals
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| Write the equation of the MonoBromination of Ethane | Br-Br + CH3-CH3 --> CH3-CH2Br + H-Br
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| Write the equation for the initiation reaction during the MonoBromination of Ethane | Br-Br --light--> Br. + .Br
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| Write the equation for the first propagation reaction during the MonoBromination of Ethane | Br. + CH3-CH3 --> CH3-CH2. + H-Br
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| Write the equation for the second propagation reaction during the MonoBromination of Ethane | CH3-CH2. + Br-Br --> CH3-CH2Br + Br.
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| What is the role of Bromine radical in the Bromination of Ethane? | Bromine radicals act as catalysts
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| Write a possible by-product of the MonoBromination of Ethane | CH3-CH2-CH2-CH3 (in the termination step) or Br-CH2-CH2-Br (further substitution of the Monobromoethane)
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| Write the equation for the termination reaction during the MonoBromination of Ethane | CH3-CH2. + CH3-CH2. --> CH3-CH2-CH2-CH3
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| How does Ozone protect us from harmful UV radiation? | Ozone molecule absorbs the UV energy and splits into O2 and Oxygen radical; the Oxygen radical reacts with O2 to reform O3 and releases heat.
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| What does the sign <=> mean? | that the reaction is in equilibrium: the rate of the forward reaction is the same as the RATE of the backward reaction and the concentration of the chemicals stay the same
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| Define an equilibrium | When the rate of the forward reaction is the same as the RATE of the backward reaction and the concentration of the chemicals stay the same
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| What is the effect of UV radiation on humans? | Skin cancer
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| What is the troposphere? | The lowest layer of the Earth's atmosphere (near the surface)
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| What is the stratosphere? | The layer of the Atmosphere that contains Ozone
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| Write the equations for the two propagation steps where Ozone is removed by Chlorine radicals | Cl. + O3 --> ClO. + O2 AND
ClO. + O --> Cl. + O2
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| Write the equations for the two propagation steps where Ozone is removed by Nitrogen Monoxide | NO. + O3 --> NO2. + O2 AND
NO2. + O --> NO. + O2
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| What is the overall equation for this propagation reaction? NO. + O3 --> NO2. + O2 AND NO2. + O --> NO. + O2 | add all the reactants on the left and all the products on the right
NO. + O3 + NO2. + O --> NO2. + O2 + NO. + O2
simplify to
O3 + O --> 2 O2
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| What is the overall equation for this propagation reaction? Cl. + O3 --> ClO. + O2 AND ClO. + O --> Cl. + O2 | add all the reactants on the left and all the products on the right
Cl. + O3 + ClO. + O --> ClO. + O2 + Cl. + O2
simplify to
O3 + O --> 2 O2
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| What is the overall equation for this propagation reaction? Br. + CH3-CH3 --> CH3-CH2. + H-Br AND CH3-CH2. + Br-Br --> CH3-CH2Br + Br. | add all the reactants on the left and all the products on the right
Br. + CH3-CH3 + CH3-CH2. + Br-Br --> CH3-CH2. + H-Br + CH3-CH2Br + Br.
simplify to
Br-Br + CH3-CH3 --> CH3-CH2Br + H-Br
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