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Ozone is formed and broken down by photodissociation in the stratosphere - Leaving Cert Chemistry - Question d - 2022
Question d
Ozone is formed and broken down by photodissociation in the stratosphere. Chlorofluorocarbons (CFCs) in the atmosphere were identified as a major contributor to dama... show full transcript
Worked Solution & Example Answer:Ozone is formed and broken down by photodissociation in the stratosphere - Leaving Cert Chemistry - Question d - 2022
Step 1
Explain the underlined term.
Answer
Photodissociation refers to the process in which molecular bonds are broken due to the absorption of light, specifically ultraviolet (UV) or other forms of electromagnetic radiation. In the case of ozone, this process involves the breaking apart of ozone molecules into individual oxygen atoms.
Step 2
Step 3
Step 4
Show by means of balanced equations the photodissociation of a molecule of CCl₃F giving a chlorine free radical and how chlorine free radicals break down ozone in a chain reaction.
Answer
The photodissociation of a CCl₃F molecule can be represented by the equation:
ightarrow CCl_2F + Cl^*$$ Following this, the chlorine free radicals react with ozone in a chain reaction, represented by: $$Cl^* + O_3 ightarrow ClO^* + O_2$$ This reaction produces chlorine monoxide and molecular oxygen. The chlorine monoxide can further react with another ozone molecule: $$ClO^* + O ightarrow Cl^* + O_2$$ Thus, the chlorine free radical is regenerated and can continue to deplete more ozone.Step 5
Explain using a balanced equation how the presence of methane in the atmosphere can help absorb chlorine free radicals.
Answer
The presence of methane (CH₄) can help neutralize chlorine free radicals through a reaction that produces chlorinated compounds.
The balanced equation for the reaction can be represented as:
ightarrow CH_3Cl + H^*$$ In this reaction, methane reacts with a chlorine free radical to produce chloromethane (CH₃Cl) and a hydrogen radical.