The Ozone Story

Question 1

1. What does a single-headed curly arrow show and when is it used?
2. Products of heterolytic fission:
3. What happens during an initiation rxn in terms of radicals?
4. Describe propagation rxns.
5. Product of a termination rxn is a stable molecule. How does this occur?

Answer 1

1. Movement of one e^-/ used during homolytic fission.^​​​
2. An anion and a cation(usually)
3. free radicals are produced
4. free radicals react with other molecules to form new radicals, new radicals go on to react to form even more radicals. (chain rxn). More than one rxn sometimes
5. two radicals react to form a stable molecule.

Question 2

1. How do you calculate overall propagation rxn?
2. Some species remain unchanged, others are made in P1 and used in P2. Suggest 2 words to describe function of these species.
3. State products made during the initiation rxn of the photodissociation of Cl₂:
4. State the overall propagation rxn of rxn mentioned above:
5. State products of termination rxn stated above:

Answer 2

1. Add both rxns together so products + product e.c.t/ cancel out any species that are both on reactant and product side.
2. Unchanged= catalyst/ used up= intermediate
3. Cl¤/Cl¤ radicals
4. CH₄ + Cl₂ ⇒CH₃Cl + HCl
5. Many diff products can be made. e.g 2Cl¤ ⇒ Cl₂

Question 3

1. Write the 2 equations for the formation of ozone:
2. Write the 2 equations for the destruction of ozone:
3. Why is the Ozone layer beneficial?
4. Why are high energy UV rays harmful?
5. How does ozone form at ground level?

Answer 3

1. O₂+hv(energy or UV) ⇒ 2O¤ / O¤ + O₂⇒ O₃
2. O₃+hv ⇒ O¤ + O₂ / O¤ + O₃⇒ 2O₂
3. Absorbs high frequency UV.
4. Skin cancer/damage to crops or/and immune system.
5. Effect of UV on NO_x and hydrocarbons /Solid carbon particles and ozone mix to form photochemical smog.

Question 4

1. How do chlorofluorocarbons break down ozone?
2. Why are CFCs more likely to cause destruction in the stratosphere?
3. Which C-X bond is most likely to break and explain why.
4. How is homogenous catalysis destroying Ozone?
5. What other free radicals can react with ozone?

Answer 4

1. C-X bond is broken homolytically to form 2 free radicals by higher frequency UV. Free radicals act as catalysts for destruction of O_3.
2. High-frequency UV is absorbed by ozone layer before reaching troposphere.
3. Carbon-Iodine bond because it has the lowest bond enthalpy.
4. Radicals form + react with ozone.
5. NO₂-NO¤, halogen and ¤OH

Question 5

1. Put the following in order: ozone layer, troposphere, stratosphere
2. Composition of air in the atmosphere and their percentages:
3. How do you get from % to ppm?
4. What radiation does the sun emit?
5. Earth absorbs some IR and most UV, what does it re-emit?

Answer 5

1. Troposphere(on top of head), ozone layer, stratosphere
2. Nitrogen 78%, Oxygen 21%, argon 1%, carbon dioxide 400ppm
3. times by 10000
4. Visible light, infrared and a small amount of UV
5. Mostly IR at a lower frequency than sun (much cooler than sun)

Question 6

1. Electrons have ……………… energy levels fixed they can jump between).
2. What excites an electron to a higher energy level?
3. Infrared makes …….. ……. ……. more causing …………..
4. Rotational energy is caused by microwaves. What happens to electrons?
5. Electrons can absorb energy so they are excited to higher energy level. Why is the amount of energy specific?

Answer 6

1. quantised
2. Visible light and UV
3. bonds bend and stretch more causing vibrations
4. cause rotation so a faster rotational energy
5. energy needed for this changes is quantised

Question 7

1. UV light can cause ………………. and ……………………..
2. Features of hemolytic fission: (3)
3. Equation linking Planks constant(h), energy and frequency(v)
4. How to calculate speed of light(C)
5. nm ⇒ m

Answer 7

1. photodissociation and ionisation
2. one e^- to each species, radicals with unpaired e^-, products have same charges.
3. Energy= h X v
4. Speed of light= wavelength in m X frequency
5. add X10^-9 at the end of number in calculator